Façades Confidential

External timber cladding: the book

2011-12-28T00:04:00.002+01:00

Langley Academy, Slough. Foster + Partners. Western red cedar

Timber facades have long been used on low-rise housing in North America and in Scandinavia. Most recently timber cladding is becoming popular in some other countries, Austria and the UK among them. Moreover, timber is nowadays being used as an external finish on medium-rise and non-domestic buildings.

But it is not easy. The main uncertainties related with using timber in facades involve: durability, weathering, dimensional change, corrosion, wind resistance and fire safety. Now, considering this long list, does it mean that timber is unsuitable as an external finish? Far from it. If design intent and construction details are in tune with its characteristics, timber can be a versatile facade material with a unique combination of performance benefits.

Architects in search of guidelines on how to use timber in facades have reasons to congratulate. This post is devoted to a recent book (released in April 2011) whose title says it all: 'External timber cladding: Design, Installation and Performance'. Its authors are Ivor Davies, a researcher from Edinburgh Napier University, and John Wood, professor of engineering at the same Scottish university. The book is more than its authors' baby. It is one of the outputs of a trans-national, EU financed project titled 'External timber cladding in exposed maritime conditions'. The project had inputs from Scotland, Iceland and Norway. More info about the project can be found here.

But this book is much more than the summary of an international study, and it is worth down to the last page if you are interested in timber for facades. In fact, it can be considered as the first true guidelines for timber facade engineering. The authors note very rightly that, during the past decade, facade engineers have tended to ignore timber in favour of more conventional - or more à la mode - materials like concrete, steel and glass. Timber exteriors have been left to architects (general practitioners) and timber specialist suppliers. This has proven risky sometimes, and reductive in most cases. Even more, the main technical standard for facades in the UK (the standard from CWCT) largerly ignores timber, whilst the existing guidance on timber cladding only covers a limited range of topics. This book comes to fill the gap between timber facade construction and facade engineering. It was about time!

The book is structured in six parts, each one dealing with the answer to six fundamental questions, exposed in a sort of 'ignorance pyramid':

What is wood?

How wet does it get?

What effects does it have?

How are these effects controlled?

How do the controls relate to fire safety?

What does all of this mean for facade engineering?

Chapter 1 describes what performance-based design means for timber facades, with a fundamental section on service life. Chapert 2, the top of the pyramid, deals with timber as a facade material, describing its main parameters. Chapter 3 covers moisture conditions in timber facades, and how to predict and to prevent them.

Western red cedar facade with pronounced staining

Chapter 4, as an outcome of the trans-national study, presents the results of site tests conducted on Sitka spruce as a timber cladding. Chapter 5 continues down the pyramid with fungal decay and insect attack. Chapter 6 goes for weathering, and how can we anticipate or respond to weathering in exposed timber cladding. In this chapter we understand why virtually all timber facades in Scandinavia are given an opaque surface coating - good to remember.

Chapter 7 adds to our limited knowledge in dimensional change on wood, and on how / why timber shrinks and moves. Good news for us: movements can be limited and estimated. Chapter 8 goes for corrosion - yes, that of metal fastenings, flashings and brackets embedded in timber. Chapter 9 describes in more depth the structural performance of timber facades - not of structures - which is an often ignored issue. Windloads, robustness of connections, dowel type fasteners and strenght grading are discussed here.

Selection process of timber design

Chapter 10 contains some of the most innovative pages: design for durability. It starts with a decision sequence to aid selection of a timber cladding design from a durability point of view - a must. It then goes down the sequence using the relevant EN standards on timber durability and preservation. It finally relates service life with timber class and use / exposure. Interestingly the authors don't take a side in the discussion pro / against wood preservatives: they present us the arguments in favour and against, so that we can decide case by case - as it should be.

Chapters 11 to 15 deal with fire and timber buildings. The fire triangle, fire testing, fire performance of timber, how to limit external fire spread, the role of air cavities, and a summary of fire regulations in the UK. Finally, a long chapter 16 is devoted to construction details for timber facades. This is an issue largerly discussed in other manuals, but again the authors bring novelty to the case, aided by clear and well drawn details. One of the good points is the treatment given to the junction between heavy (brick) and lightweight (timber) cladding.

The book ends with an updated and interesting list of appendices and references, among them the British and European standards on timber for panelling and external cladding.

Horizontal timber cladding details

In summary: if you are tired of simple and often repeated statements about how timber facades work, and want to know what is really going on and how this should inform your design decisions, this is your book. The authors challenge some of the prevailing assumtions about moisture, its effects and how they are best controlled. New light is shed on how moisture issues affect, and are affected by, the need to ensure that fire safety is fully addressed. And the construction details are based on a combination of new experimental data and a fresh appraisal and synthesis of existing information - they deserve a look and some thought, not just a copy-paste!

Go and buy it. You'll find the link to the publisher at the title of this post. It's not cheap, but it's worth every penny.

Cupples Products: a Tall Tale of American curtain walling

2011-12-17T13:13:00.048+01:00

History is unfair with master builders. Do you know the relationship between these four behemoths of the 20th century architecture: the John Hancock Center in Chicago, the Twin Towers in NYC, the Sears Tower in Chicago and the Hong Kong & Shanghai Bank headquarters in Honk Kong? The relationship is their skin. The curtain walls and external cladding elements of these four buidings were designed and fabricated in the same place: a factory in the plains near Saint Louis, Missouri.

Webb and Knapp Tower in 34th Street, NYC. I.M. Pei

That place had a name that was equivalent to glazed facades during the great decades of the sixties and seventies: Cupples Products Inc. To whom does that name recall anything? Well, ask Norman Foster or I.M. Pei (or Gordon Bunshaft from SOM or even Mies himself if they were alive). Of course, they would answer: Cupples was my curtain wall contractor of choice back then.

That was back then. Today, if you search Cupples in Google you get files from old legal actions and their last address, a suite in Saint Louis. The nearest website is a link to Enclos, the curtain wall company that lastly absorbed Cupples know-how in curtain walling at the turn of the millenium.

There is something to learn from this company, parallel to the growth of US cities in the second half of the 20th century. Cupples was one of the very early entrants into the new industry of curtain walling right after the war ended. Started in 1946 as a manufacturer of residential of window products, the company rapidly progressed into the design development, engineering, fabrication, assembly and field installation of custom curtain wall systems. Cupples became a provider of glazed solutions to architects and builders eager for new facade technology. One of their first client architects was I.M. Pei, for whom they delivered the curtain wall of Webb & Knapp Tower in 34th Street, NYC. This building was built in 1954 for the headquarters of Webb & Knapp , a local tycoon similar to Donald Trump, for whom young Pei worked as an architect during his early career. Pei would remain linked to Cupples as we will see.

U.S. Air Force Academy, Colorado. Cadets Chapel. Skidmore Owings and Merrill, 1959-1963

At the end of the fifties Cupples start working for Skidmore Owings & Merrill, another architect - contractor collaboration that would last long. The U.S. Air Force Academy in Colorado (with its characteristic Cadet Chapel pictured above, finished in 1963) is the most prominent of these early works. It is interesting to note that the chapel has just been refurbished, fifty years after completion. See the SOM webpage for details.

In the fifties and sixties curtain walling was an integrated business. In a way not rivalled by the biggest Chinese suppliers today, Cupples factory included under one roof these production lines: aluminium extrusion, anodizing and liquid coating, cutting, punching, drilling, curving, bending, mechanizing and assembly of curtain wall units. Their designers were able to study and solve the intricacies of a very complex facade; while at the same time they would deliver off-the-shelf simple systems as Horizon, a stick curtain wall very popular up to the nineties.

Lake Point Towers, Chicago

In 1960 Alcoa, the aluminium giant, buys Cupples and the great story begins for the guys in Saint Louis. The sixties was the era of the sheer towers. New York adopted a zoning resolution encouraging architects to set off their buildings and to enrich land use. The new towers were pulled in from the building line to form landscaped plazas and obtain the maximum permissible sheer height. Soaring from open plazas, aluminium and glass enclosed buildings dominated the US cities. Curtain walling technology also experienced a jump forward: more sophisticated engineering and manufacturing techniques were developed, as pressure equalization and laser technology. Cupples introduced and became a leader in color anodizing.

The sixties were the golden years for Cupples. The list of buildings whose facades were clad by Cupples this decade is simply extraordinary.

To the left, the Lake Point Tower Apartments, a project of Schipporeit & Heinrich in Chicago finished in 1968. The link to Mies Van der Rohe is obvious, although this is not a Mies's work. Please have a look at this video from 1969 - the third part of three explaining how the tower was built - here dedicated to curtain walling. A real piece of art for us conoisseurs. Cupples worked for Mies in at least two projects: the Pavillion - Colonnade apartments in Newark and the One Charles Center in Baltimore. Two minor projects for the German master but equally interesting.

Another project from the sixties, the John Hancock Tower in Boston, with I.M. Pei & H.N. Cobb (below left). It was actually completed in 1971, but was not opened until 1976. This is the famous (or better infamous) 'plywood building', so nicknamed because of the glass failures it suffered right before completion. This is still the perfect case study for climatic loads acting on insulated glass and how to avoid them - by reducing the stiffness of the bonding between the inner and outer panes of glass. But this is another story.

In San Francisco we find a good example of the decade: the Wells & Fargo Tower, finished in 1966 by John Graham (one of the corporate architects in those days). A very elegant and slender tower, better than most of the SOM buildings in the decade. I am not sure if the vertical shiny cladding is stainless steel or anodized aluminium, but in any case it reflects prosperity and optimism (see picture below right).

Left, John Hancock Building in Boston, I.M. Pei. Right, Wells & Fargo Bank in San Francisco, John Graham.

Back to Chicago and we find one of the real giants: the 100-storey John Hancock Center, with Bruce Graham and Fazlur Khan (both from SOM) as main architect and main engineer respectively. Completed in 1969, its curtain wall took 2.5 million pounds (1,100 tons) of aluminium and brackets and 300,000 sqf (28,000 m2) of glass.

The John Hancock Center in Chicago by Bruce Graham and Fazlur Khan from SOM, finished in 1969.

During the installation of the John Hancock Center in Chicago, in November 1967, Cupples changed hands for the second time: Alcoa sold it to the metal company H.H. Robertson, and Cupples became Cupples Products Division within Robertson. The new boss was a giant of metal cladding and steel elements for slabs and ceilings, and would soon begin to be well known by their sandwich panels, branded as Formawall. Cupples had a unique position as the only aluminium and glass supplier in the conglomerate, thus allowing Robertson to provide one-stop-shop services for structure and cladding all around the world. Cupples employed 850 persons and was present in curtain walling, aluminium doors, window frames, store fronts, entrances and suspended ceilings at the time of Robertson's take over.

Between the sixties and the seventies, and both in Chicago, these are the two other big buildings clad by Cupples there: the Standard Oil Building and the Sears Tower. The Standard Oil Building, finished in 1972-73, has another interesting story of failure due to the Carrara marble cladding used (not by Cupples) which failed due to bending - a process known as thermal hysteresis. The solution was hard: to remove the whole marble cladding and to replace it with light coloured and thicker granite panels at an incredible cost.

Left, the Standard Oil Building in Chicago by Perkins & Will with Edward Durrell Stone. Right, the Sears Tower by SOM.

The Sears Tower, once again by SOM and finished in 1973, will deserve a future post only for itself, so no more comments by now.

We are now well into the seventies. The construction of the World Trade Center in lower Manhattan is going on and Cupples people are busy with fabrication and erection of the two towers, which by the time would be the tallest in the world. Minoru Yamasaki and Associates with Emery Roth & Sons were the architects. Skilling, Helle, Christiansen and Leslie Robertson were the engineers. Tishman was the general contractor.

World Trade Center towers in lower Manhattan, 1973. Minoru Yamasaki and Leslie Robertson.

Many new design, engineering and construction techniques were required for the structures. The exterior skin was 2-million sqf (185,000 m2) of Cupples aluminium curtain wall. It used a then unique and progressive 'pressure equalizing' design which caused wind loads and pressures to be exterted directly upon the building structure rather than the aluminium skin. The steel frame work forming the exterior wall was installed by hoisting in place 3-module opaque prefabricated units, up to 36 ft high and 10 ft wide (11m high x 1m wide). Horizontal aluminium spandrel units - finished with Alcoa Duranodic bronze - were then spliced onto the adjacent unit. All aluminium profiles and sheets was supplied by Alcoa.

The two buildings included more than 44,000 glass vision units, recessed 10 inches in relation to the external column cladding, achieving some degree of protection from direct sunlight. Another very interesting feature was the anchoring system of the curtain wall to the bottom side of the floor slab. A viscoelastic interlayer between the bracket and the main structure allowed for wind gusts to be transferred but it absorbed part of the dynamic vibration of wind action. It remains to be studied what role - if any - did this viscoelastic shock-absorber have at the time of the planes crash in 2001...

WTC towers during construction. The yellow band between the curtain wall and the steel structure was the area of structure undergoing sprayed fireproofing.

Cupples completed some more interesting projects in the US during the seventies and the eighties. Among them it is worth mentioning two projects of Johnson & Burgee which exemplify the new style of architecture swifting to volumes out of the box or to pure postmodernism. The Garden Grove Community Church in California (aka the Crystal Cathedral) was finished by Cupples in the late seventies.

Garden Grove community centre (also known as the Crystal Cathedral) by Johnson and Burgee

The Republic Bank Center in Houston, clad with units of pink granite and glass, is a perfect example of the eighties reaction to sheer transparency, which was not bound to last. Another interesting example of big space container made by Cupples is the State of Illinois Center in Chicago, by Murphy and Jahn.

Left: Republic Bank Center in Houston, Johnson & Burgee. Right: State of Illinois Center in Chicago, Murphy and Jahn.

Republic Bank Center, stone curtain wall horizontal details. Above section @ vision glass, below section @ spandrel

The next - and probably the last - of the great buildings ever to be covered in glass and aluminium by Cupples was not in the US but abroad: the Hong Kong and Shanghai Banking Corporation headquarters in Hong Kong by Norman Foster, finished in 1985. This is a very successful and rare case of project management led by the architect. Foster proposed the Bank to arrange a team of specialists - architects, engineers and contractors - under a sort of design & build contract where architects were the leading partners both during design and construction.

HSBC headquarters in Hong Kong by Foster, 1985: the most expensive corporate building in the world...

The merit that this scheme could go well can be mainly attributed to Foster's bold vision, but the other players - Arup and Cupples among them - were also critical. It is worth mentioning here the role of Phil Bonzon, the engineer from Cupples that led the design and construction of the facade throughout the whole process. Bonzon's sketches were unanimously praised by Foster team members as the only way for them to understand the intricacies of what they were jointly designing. Again, the cladding of this building deserves a future dedicated post if not a whole PhD thesis...

Phil Bonzon's sketches for the HSBC facade design. These details prefigure many industry design features by at least ten years

Nothing can last forever. Cupples lagged behind during the nineties, due not to a specific reason but probably to a number of them. In my opinion the management team did not anticipate that the one-stop-shop model of vertically integrated production was untenable. Cupples people kept for too long a manufacturing structure that was becoming costly and outdated as years passed. The parent company, H.H. Robertson, was also under a similar stress.

Besides, Cupples was not alone in the market. A later entrant to the curtainwall industry had been operating over the decades under the names of Harmon Contract, Harmon Ltd, and finally Enclos Corp, completing many landmark projects. By the end of the 20th century the two companies, Harmon and Cupples, were operating as sister companies under the same umbrella with Harmon focusing on the domestic US market while Cupples tried to keep pace with international operations. Finally, the two companies became one under the same name, that of Enclos. It can be said that Enclos has inherited and continues Cupples history into the twenty first century.

Internal view of the assembly line during the eighties

Why am I interested in Cupples? Because of a personal reason. In 1991 I entered the facade business as project manager with Robertson in Spain, dealing with curtain wall projects and working closely with a number of some great American Cupples colleagues, then busy with projects in our country. I learned the first curtain walling lessons from them. People as Rick Hamlin, now in Trainor Glass; or site managers as James Jutson or Tom Watson, a couple of great chaps whith whom being on site was never boring. Those guys taught me the important lessons. That a facade design is not completed util it is installed - design, fabrication and installation being all part of one same process. That many things can go wrong along the process, and one has to be awake and alert to avoid mistakes and correcting them when things happen. That every step should be checked and re-checked before moving to the next one: it saves time, nobody is perfect. That, in summary, a building and its facade is a lineage of decisions made by a bunch of different people, and success is an outcome of everyone, not of the first one in the line. That being humble on site goes along with being better.

I will never forget those brown helmets with the Cupples name on top. Others will come and build great facades with promising new technologies. But we should never forget those who were so good at opening the trail before us. We owe it to them.

The Louvre pyramids revisited

2011-12-04T18:43:00.003+01:00

Yes: pyramids in plural. This post will compare the main Louvre pyramid (the one we all remember) with the inverted pyramid, less known but equally noticeable. Both are of course part of I.M. Pei's plan for Le Grand Louvre in Paris, commisioned by President Mitterrand as the first of his 'Grand Ouvres'. But as we will see the similarities between the two end right there. The main pyramid epitomises the end of the structural frame era, while the inverted pyramid represents one of the first examples of our time, the supremacy of structural glass.

An unusual view: the main pyramid seen from the top of the inverted one

The main pyramid - together with its three small siblings surrounding it - was finished and opened to public in 1989. The inverted pyramid was not completed until 1993. On the earliest sketches made by I.M. Pei back in 1983 the main pyramid, surrounded by the other three and the pools was already there. The inverted pyramid came slightly later in the plan, around 1985, as a standing point marking the entrance from the underground and the parking.

The main pyramid (centre) and the inverted pyramid (right). The underground entrance takes place from the right.

Pei wanted the main pyramid to be the new entrance to the Louvre, so that people had to wait on the Napoleon court to enter the museum. But this proved not enough to manage the thousands of people arriving every day. Soon predominance was given to the underground entrance, be it from the tube line of from the parking lot. Both coincide precisely at the inverted pyramid, so that it now becomes the first glass feature to be discovered by visitors.

The inverted pyramid between the gardens and the main one

Why are these two structures so different? Aren't both of them just glass pyramids? Well, not exactly. The first difference is their size. The main pyramid has a square base of 35.4m and a height of 21.6m, while the inverted one has a square base of 15.5m and a height of just 7m. Another reason for the two structures to have been designed different is wind load. The main one has to withstand strong wind loads that don't exist in the case of the inverted pyramid. To be precise, the inverted pyramid top side (which by the way is a very low pyramid in itself) only has suction loads due to wind. But the main reason for these two structures to be remarkably different is a fact of evolution: the engineers who designed the main pyramid remained under the old paradigm of glass as an infill; the engineers that were given responsibility to design the inverted one were pioneers of the new paradigm of glass as a structural element.

It has taken me a while to find out who the main actors are in this play in two parts. From the architect's side it is clear : I.M. Pei from Pei & Partners (now Pei Cobb Freed & Partners) was the design principal. Second in charge was Leonard Jacobson, although the design architect in charge of the pyramids was Yann Weymouth. Yann's sketches between 1983 and 1986 are the visual history of the design process, both in general and in its details.

Yann Weimouth and I.M. Pei on site during the main pyramid construction

Studies for tension fastening of the main pyramid. The left version was the selected one. Sketch by Yann Weymouth, April 1985.

Yann, who was fluent in French, lived in Paris between 1984 and 1990. The associate architect (the French local) was Michel Macary.

The 'serres' at La Villette by RFR, 1982-86

Now comes the conundrum of the story: the engineer's selection. The best engineering firm in glass tensed structures worldwide was at the time very active in Paris: RFR, Rice Francis Ritchie. This team of one Irish engineer - Peter Rice - and two British architects (Ian Rithchie was 100% architect; Martin Francis was partly a yacht designer) was created in Paris in 1981. RFR had successfully completed the 'serres' at the Parc de la Villette between 1982 and 1986, so they had to be well known to Michel Macary or to Emile Biasini, Mitterrand's man in charge of the whole project. How then RFR were not given the task of engineering the pyramids? The answer - as much as I can guess - must be found in I.M. Pei's contractual conditions: Pei was made 100% responsible of the design without any interference from French officials or local establishment. This included of course the selection of his engineers - which would be his and not a French firm if he wanted to build his Pyramid as pure as he wanted. It is a real pity that Pei was not right in this point - surely without knowing it at the time.

So the selection for the engineer was made by Pei, and Pei chose the Canadian firm of Nicolet Chartrand Knoll Ltd. What did this firm exactly do at the project? Their role seems to be clear for the large underground concrete structures. Let's not forget that the main pyramid sits atop a 2m-thick concrete slab with large spans. The stair connecting the Napoleon court with the bottom level is also a feat, with its 540º self-supporting curve. As Nicolet Chartrand Knoll refer to the Louvre pyramid in their webpage French version "The scope for the structural engineer, as bluntly expressed by the architect I.M. Pei, was that of building a structure as transparent as technology could reach. Through a close collaboration between the architect, the structural engineer and the other professionals it was possible to reach a successful outcome. Out of about 25 different structures which were studied, one was finally selected ".

Now, letting aside the fact that they studied many options, was the final structure of the main pyramid as transparent as technology could reach by 1986? I humbly disagree, and it seems that Mr Pei was not too impressed by its transparency either. The main point is a conceptual one: this is not the design of a glass pyramid, but the design of a steel pyramid clad with glass. Glass is just filling the space between the stainless steel struts, it is not taking any structural role. As Mick Eekhout - the Dutch structural glass specialist - would put it, the main pyramid is an example of space frame with integrated glazing. The two details below compare a structure of the mid-80s with the main pyramid detail:

Left: a Mero space frame with integrated framing. Right: the top detail of the main Louvre pyramid

The Louvre solution is fairly more integrated than a space frame with a separate glazing as the Mero structure with glass on top. The outer mullions have disappeared and now a fairly thin aluminium profile is receiving the glass panels. But the glass is simply sealed at four sides with silicone; it is not making part of the structure at all. Suppose we take out all the rhomboidal glass panels: nothing would happen to the structure, the pyramid would remain in place. The pictures from construction period show this quite clearly. Images below have been taken from the book 'I.M. Pei. The Louvre pyramid' by Philip Jodidio, Prestel. It also has great sketches from Yann Weymouth.

Glass being installed at the main pyramid. There was practically no internal scaffolding in this picture. Notice the bespoke cradle to attach the suction cap to the pyramid.

Scheme of the steel structure of the main pyramid. Left: steel tubes in rhomboid shape with cables and stiffeners. Right: the same with glass already in place.

Stages of glass installation on the main pyramid

If the main Louvre pyramid was an American-Canadian design, how come did RFR start working for this pyramid - and yes, much before the inverted one was started? There are two reasons for that, and probably the two were required. The first reason is to be found in the (French) facade contractor: Eiffel Construction Metallique, precisely the same facade contractor that had undertook the building of the serres at La Villette some years before. The Eiffel guys entered the design team for the Main Pyramid when it was still in the drawing table - remember: 25 models were studied before concluding on one. They must have seen that the Canadian engineers, expert as they were in concrete structures, found themselves a bit lost with the cables and rods of the pyramid. So Eiffel managed to sub-contract RFR as their experts to discuss design subtleties with the Canadians.

Node detail with tubes, bars and cables

The second reason was Peter Rice. He was at the time part of two companies in parallel: Arup - his first employer - and RFR - his new baby. A strong Arup engineering and lighting team, directed by Rice, was working at the same time on the Richelieu wing of the Museum, taking care of the glazing of the three big courts (5,000m2 and 450 tons of steel in total) and of the natural lighting strategies for the whole Richelieu wing. Thus, Rice was already known to and appreciated by the 'proprietaire'. I can imagine Peter Rice inviting Emile Biasini (the boss on site) to take a taxi and visit La Villette sometime during the works.

Since Rice was engaged with the Arup team, the RFR consulting work for the main pyramid (remember, under the hat of the facade contractor) fell on Martin Francis. Martin was an architect but also a yatch designer. The whole concept of suspended glazing and stainless steel cables owes in fact a lot to the yatching world of mast connections. As part of his sailing activities Martin knew of an American company who were masters in stainless steel rods, cables and riggers for naval architecture. The company name was Navtec and Martin Francis' colleague there was Tim Eliassen. This becomes interesting, and a prove that mixing technologies is always productive. Eliassen, who had studied aeronautical engineering and graduated in nuclear reactors had cofounded Navtec to end up immersed in the world of large sailing yachts, America's cup boats and the like.

Inner transparency, so much sought after by the architects, depends largerly on the point of view.

According to Mic Patterson (himself a good friend of Tim's and as such a reliable source), in 1987 Elliassen received a call from Francis telling him that there was a project in France that needed his involvement. The main pyramid became the first architectural project for Navtec, where they provided about 3,800 'short pieces of yatch rigging' to Eiffel. After completing the Louvre pyramid Eliassen tried - unsuccessfully - to convince his colleagues of Navtec to enter the business of glass architecture. Navtec comment at the time, according to Patterson, was unforgettable: "roofs leak, you get sued". So Eliassen founded TriPyramid Structures - notice the relationship between the name and his first job - in late 1989 and started a long line of high-profile projects, helping US architects to master in the new science of glass and steel. But that's another story.

The complexity of connecting elements next to the bottom of the pyramid. Notice the air fans pointing towards the inner face of glass, intended to reduce the risk of condensation.

A side note about glass selection for the main pyramid will give perspective on how much things have changed since the mid '80s in glass technology. Pei wanted a glass as clear as possible, and he was sure that the required laminated thickness (and even more in diagonal views) would be seen as green form the outside. So under his pressure a new manufacturing process was devised using Fointanebleau white sand -that is, sand very low in iron content - in collaboration with the French firm Saint Gobain. Possible it was, but expensive: the cost of producing a small batch of low-iron glass was huge at the time, and the big boss at Saint Gobain wasn't willing to stop the furnace and introduce such an order. Pei has declared (it's in Jodidio's book) that he went to Mitterrand in person in order to get the glass he wanted. Those were the days: the Emperor stopped the furnaces and glass for the pyramid came out as clear as it had to be...

Section of the concrete slab below the glass pyramid. This was the kingdom of Nicolet Chartrand Knoll, the Canadian engineers who started designing the pyramid concept.

So the main pyramid ended as best as it could, still not as 'trasparent' as Pei wanted, but it would have a great influence - much larger than the serres of La Villette - in expanding the word of the new structural glass facades to the world.

Now, Martin Francis had shown Pei how useful it had been to have RFR on board for the main pyramid, and Pei awarded them with the contract for the inverted pyramid. For RFR the next logical step in the linear sequence of the history of glass had to be the disappearance of mullion frames, elevating glass to the primary structural element of the builiding's skin. And this is exactly what happened with the inverted pyramid: the flat, clean glazed surfaces of La Villette lost their ugly steel tube edges and became a pure glass-enclosed volume. The inverted pyramid is to structural glass what the Seagram building was to the history of curtain walling: the culmination of a de-materialization process that had taken years to achieve. And, Pei permitting, the main pyramid with all its glamour would be nothing but the Lever House, located - as its sibling - just some feet away from the real jewell...

Enough for this post. It's too much text already. Let me finish with some good images and drawings of the inverted pyramid. From the heights of our age it's easy to read and to understand how it works. It surely must have been painful to design, but there it will remail, the light of a candle, forever.

Inverted pyramid as seen from the Carousel

Inverted pyramid: section and structural diagram

Inverted pyramid from below

Inverted pyramid: more structural diagrams

I.M. Pei at the bottom of the inverted pyramid

Inverted pyramid: the square brackets support the top square glass units while the cross brackets support the sloped rhomboid glass units.

Me as Peter Rice, hanging from cables...

Detail of the top glass brackets. Each glass unit is glued to one side of the bracket at each corner. Slope is 4º for water drainage.

Detail of the side glass brackets. Each glass unit is drilled at the corners. The bracket is a mirror piece to avoid swinging and provide additional stiffening.

The Steiff factory and the birth of curtain walling

2011-11-27T17:06:00.023+01:00

The question of what building in history has the first curtain wall hides a tough academic battle. Here - as almost everywhere - Europeans and Americans diverge. I don't have a strong favourite. What I have is a list of the first curtain walls erected before 1950 that matter to me; and they happen to be located at both sides of the Atlantic.

Among the Europeans, the Fagus headquarter by Walter Gropius, built in 1911, is celebrating its first 100 years now. Among the Americans, the Halliday building in San Francisco (1917) is a must; same as the Equitable Building in Portland (1946), a forgotten jewell from Pietro Belluschi. Now that I think of it, it would be good to re-visit most of these great oldies in future posts.

The east block from 1903 is the front pavilion to the left. The others were built between 1904 and 1908. Picture from the early 1920s.

This post is devoted to one of the first real curtain walls (not a shop front or a wintergarden) ever built, the east block at the Margarete Steiff AG factory in Giengen, erected in 1903. One thing can be said for sure: this was the first double skin facade ever built and - not surprisingly - it had to be located in Germany. Most of the information for this post comes from a paper whose title couldn't be more clear: "The invention of glazed curtain wall in 1903 - The Steiff toy factory". The paper was presented at the 3rd International Congress of Construction History (Cottbus May 2009) and was written by A. Fissabre and B. Niethammer from RWTH Aachen University. More information about the Steiff factory can be found at the Docomomo Webpage on the building.

Europe’s most celebrated soft toys, the teddy bears with a button in their ear (‘Knopf im Ohr’) are still manufactured in this all-glazed factory building located in the small town of Giengen, 32 km north-east of Ulm. Margarete Steiff (1847-1909), a native of the town was partially-paralysed at the age of 18 months, but from a dressmaking studio in her father’s house she established a successful company making felt toys. Her nephew Richard Steiff was largely responsible for the company subsequent growth.

The original factory building as it is today. Note the diagonal bracings at the large elevation.

Between 1902 and 1903 Richard Steiff took two revolutionary steps: to include bears (sitting bears to be precise) as part of the company toys portfolio and to design a new factory building to cope with the increasing international demand of felt toys.

Teddy bears for the American market were in fact the reason behind the construction in 1903 of a new iron and glass building, 30m long, 12m wide and 9.4m high, with an outer shell consisting of a continuous double-glazed wall and a flat roof. The three floors within are supported on iron lattice-work columns. The iron castings and forgings were designed and provided by Eisenwerk Munchen AG, a German contractor. The east building was subsequently extended with two more pavilions between 1904 and 1908, built in timber structure for economic reasons but all with the same double glazed facade.

Richard Steiff's intention realised: an all-glazed, well-lit building to increase productivity in toys assembly

Inner view of the Fagus office wing, Gropius 1911

Look at the image above, and compare it with similar images of the Fagus factory in Alfeld by Gropius, to be built only eight years later. In Alfeld they made shoe trees, here in Geingen they made felt toys. Both activities required natural light. Alfeld is located at the north of Germany, Geingen is at the sunnier south. Natural light inside the Steiff factory is everywhere; if it were not for the clothings and the bulb lamps the image above could be almost contemporary. Look at the curtain drapes at the facade corners: they were there to protect from excessive sun radiation in summer.

Was Richard Steiff (the company founder's nephew) interested in a brand new industrial aesthetic or was he looking for an engineering ideal? Clearly not at all. He was a toy industrialist himself - he was looking after a continuous workshop plan, well illuminated, where productivity could raise and costs be kept under control. He was also in a hurry: in 1902 the company had received a first order of 3,000 teddy bears from a client in the USA, and subsequent orders were expected. More production space was needed but it had to be efficient, well lit and built quickly.

Richard Steiff with a teddy bear

Richard may have taken over some constructive ideas from his father, Friedrich, who was employed in the building sector. According to the paper by Fissabre and Niethammer, Friedrich Steiff might have been influenced by new iron-glass constructions when he visited the Great Exhibition in Chicago in 1893. Upon receiving these ideas from his father, Richard did not only try to realise them but also to improve them. Maximising light was not an easy task as the planning authorities feared workers would go blind in a glass house. But the permission was given and construction could finally start.

Richard Steiff contracted the Eisenwerk München AG company to design and build the structure of the new factory. It remains unclear who proposed and decided it, but steel was the obvious material for a quick and fire-proof structure. The plans and details of the riveted and wind-braced steel frame were drawn by Eisenwerk München, as shown in the plan drawing shown here below. The three-storey loft, covering an area of 12 x 30m, has a slightly inclined single-pitch roof made of galvanised iron sheet. Inside it is divided in three naves each formed by five bays, punctured by rows of six load-bearing columns each.

Second floor plan as shown in the building-permission documentation, 1903. Note the L-shaped ramp for Ms Steiff's wheel-chair extending from bottom left up to top right.

The main structure of the building (located at the corners) consists of four L-shaped external pillars, riveted on several plates and angle sections. They are linked at the bottom with a lattice truss running around and set in concrete, thus guaranteeing the solid fastening of the frames. The lattice truss is also the basement of nine facade columns of I section set in each of the longitudinal walls, transmitting the perimetral forces onto the ground. The intermediate and short-side facade columns are composed of two U-shaped beams, conntected by small sheet metal streps (see images of the interior above and of the construction below).

The load-bearing structure is reinforced by two long diagonal braces on each side of the long facades and cross-butressed ceilings at each floor level. This composition provides three-dimensional stability with a minimum dead load. Prefabrication and dry-fix connections are a fundamental part of the concept, a combination between Marcel Lods and Mero structures but built fifty years before. Even the Maison Dom-ino concept by Le Corbusier would come much later, in 1914-15.

Construction site in 1903. Note the four corner columns, the nine longitudinal pillars above the lattice truss and the intermediate set of six columns each. The top beams and the diagonal bracing are not instaled yet.

Now it's time to talk about the envelope, the really revolutionary innovation in this small building. The external cover consisted of a double skin façade on all elevations. The inner glazing skin goes from the upper edge of the floor to the lower edge of the ceiling, whereas the outer façade covers the total height of the building. If the inner skin could be understood as a large glass shop-front, not dissimilar to other examples in New York, Chicago or Berlin, the outer skin is nothing but a pure curtain wall. It floats above the facades suspended from the top level; it runs continuously around all three floors, it is attached to the columns to transmit wind loads, and it was conceived as a cavity between two transparent skins to improve its thermal performance whilst allowing natural light.

The columns are located inside the air cavity

The facade had been planned from the very beginning as a double-skin construction for heat insulation. The thermal insulation is achieved through an air cavity of around 25cm floating above the envelope. Air exchange is possible by opening box-type windows in every floor, which don't interchange air with the cavity. Additionally, the building was equipped with a low-pressure steam heater - new at the time - that kept the internal temperature stable in winter.

Corner detail and section / elevation, taken from Glass Construction Manual, Schittich et al 1999

What about summer conditions and solar heat radiation? It is clear that the workers did not become blind due to excessive light, but they surely were not happy working in summer under external high temperatures, equally high inside the building. How could solar radiation be mitigated? First, the glass is not transparent but matt, a cheaper version at the time. Matt glass has a slightly lower solar factor. Second, the factory owners used a combination of curtains and cross-natural ventilation to keep temperatures at least not higher than the outside ones. Air conditioned, already invented by Carrier, was of course not an option here, although ventilators were installed later on. It is ironic that exactly the same problem and the same 'natural' mitigation strategy was followed at the Crown Hall building in the IIT campus in Chicago, many years later. Mies van der Rohe was simply learning the same hard lesson again.

Vertical section of the double skin facade, taken from Fissabre & Niethammer 2009. Ech glass pane is 3mm thick. The cavity was communicated along the whole height.

One last detail that struck my attention when preparing this post: where are the stairs? As the plan above shows, there seem to be no stairs inside the factory space. Instead, a ramp was designed that, starting from the ground floor, provided access to the first floor and to the second one from the outside. The main reason for this unusual feature has to be found in the company founder and boss, Ms Steiff's handicap. I can imagine Ms Steiff as a strong minded woman, travelling up and down the ramp in her wheel chair. But there is a second reason, also quite practical. Building permission is given (and taxes are paid) based on the built covered space. A nice internal stairbox would have detracted a noticeable percentage from the net usable area. An external ramp, especially if it was required by a handicapped person, was an excellent alternative that had no impact on the inner space. Again, German passion for efficiency at its most!

The ramp at the back of the Steiff factory providing access to the first and second floors. Picture taken around 1903-04.

What was the influence of the Steiff curtain wall in the European architecture? The hard truth is that there were no lessons learnt from this early example of curtain wall application, simply because nobody decided to pay any attention. Why was the Steiff factory so completely ignored at the time?

First, because the project was not signed by an architect. We now know it couln't be otherwise: an architect would have considered the whole concept too unpalatable. It was not until Gropius developed what he had learnt working for Peter Behrens at the Fagus factory that light was made upon the curtain wall as a respectable facade solution.
Second, the place was not central to anything. Giengen is still today a nice small town, with a German mid-size industrial park devoted to toys and fire-proof systems. It was not in Berlin, the Rühr or Frankfurt.
Third, the company was not AEG or Messerschmidt. Steiff is well-known today but only among toy collectors. It was completely unknown at the beginning of its growth in 1903.

Scheerbart (left) and Bruno Taut at the Glass House, 1914

All said, it is a real pity (or a shame) that architectural critics were so blind about what was happening around them. Sigfried Giedion was too young, Muthesius or Tessenow were too interested in the handcraft work to notice about steel, glass or modern factories. The glass guru of the time, the poet Paul Scheerbart, would not write his very influential "Glasarchitektur" until 1914. And by then things had taken another direction. In summary, Richard Steiff was not the right man, not in the right place, and definitely not in the right time to become influential. He had arrived too early. But he still deserves a big part of the credit. Now we know.

Open I Close: the new Scale series by Birkhauser

2010-12-15T00:03:00.005+01:00

The Birkhauser construction books are a source of never-ending information, that grows larger every year. Some may criticize the fact that authors and themes are too German-oriented, understandable for a Basel-Berlin located publisher. But truth is, in my opinion, that if Birkhauser did not exist, we would miss it - and a lot!

There are many more books there apart from construction. In architecture the list is long and with some big names (Le Corbusier complete works to name just one). But that doesn't make Birkhauser unique: their uniqueness in the world publishing scene is their capacity to push the best known specialists in construction to write, to draw and to expand the knowledge of world readers - in spite of the German touch, or maybe because of it?

A friend has brought to my attention a book from 2010, titled 'Open I Close. Windows, doors, gates, loggias, filters' This is the first book of a collection called Scale. The second book of the series will be released shortly, 'Enclose I Build'. According to the Editors' foreword, 'The Scale series (...) provides illustrations at various different scales and with various degrees of abstraction, wich demonstrate the interrelation of space, design and construction' Judging by the first book of the collection, I would say that the degree of abstraction is a bit too high, and the technical scale is somehow lost in translation.

Open I Close examines architectural openings, from idea to implementation. The authors did not see the need to have a Contents page, which I see as a bad decision, so here it goes: Introduction - Windows - Filters - Doors and gates - Case studies - Appendix. I was intrigued because Loggias, one of the promises of the title, are not a chapter: in fact, loggia is a word almost non-existing along the book, apart from the title. A real pity.

The Introduction is poetic to say the least. Issues covered here range from 'Atmosphere' to 'Passageway, threshold and entrance' to 'Spatial openings and intermediate spaces' to 'Ambience and materials'. Luckily it's not too long. The second chapter, Windows, is the longest and at least to me the most disappointing. Aluminium windows and plastic windows share one page of the chapter. Enough. Window hardware (that is, fittings and the like) deals with old drill-in hinges, cremones and espagnolettes used in ancient timber windows, but tilt and turn fittings (covering 85% of all windows installed in Germany, as we learn) don't have a simple illustration or a technical description. Another pity.

The third chapter, Filters, covers sun and glare control systems, shutters, blinds, curtains and screens. To say 'covers' is a figure of speech: it runs short and passing through all these points. Chapter four is devoted to Doors and gates. Again: fire rated doors and emergency exits (both) can be dealt with in one page, one page meaning a short column of text and one big sketch. Chapter 5 brings us nine Case studies. We had been promised at the Introduction that the examples would be both practical and generally applicable. Maybe, but at least that's not the case with the conversion of the Moritzburg castle in Halle, by Nieto Sobejano. The project is one of the more interesting ones, the problem is that no openings are brought to our attention apart from one small section of a skylight in a nice roof construction - clearly not an opening in itself.

The book ends with an Appendix that includes several tables and information pages. If your project is in Germany and you don't speak German, it will be of help. There is a list of standards, most of them DIN and EN but not complete and maybe not too reliable either. DIN EN 12208, dealing with watertightness of windows and doors, comes under the heading 'Doors - Thermal insulation'. Would you say DIN EN 14351-1, the product standard for windows and external doors, the standard on which CE mark for windows is given, should be in the list, maybe under the heading 'Windows - Planning in general'? You got it: it's not there - nor anywhere else, but you can enjoy DIN 107 instead, titled 'Left and right designation in construction engineering'. A pity once again.

Then there is an 'Associations and manufacturers list'. All associations are German. No problem with that, but couldn't the authors (three architects from TU Darmstadt) do some Google digging and add the equivalent British, French and maybe US counterparts? Manufacturers are from... yes. Reynaers is in the list because they have an address in Gladbeck. Technal is not in the list - OK, too French. But Wicona, a great supplier from Ulm providing aluminium window systems all around Europe, is not in the list either! Why?

My friend paid 49,90€ for this book. I arrived too late to tell him that he should have invested less than half that quantity in buying another Birkhauser book, a much humbler one: Facade Apertures from the Basics series. Its cost? 12,90€. The amount of valuable information? Quite the same, with less nice colour images for sure. This - having arrived late with my advice - is the biggest pity indeed.

ThyssenKrupp Quarter facades: a giant's gentle skin

2010-12-04T10:32:00.021+01:00

Some great buildings pass unnoticed below the radar of architectural intelligentsia. And not because they are small or built in lost places, but because they are too 'client oriented'. If a corporation is satisfied with their new HQ building, its architectural quality must have been low, or so the thinking goes. This post describes a recently finished great group of buildings - two times great, since they are both architecturally compelling and they perfectly reflect their owner and user's vision. If this group of buildings is interesting in a number of ways, one of them is the facade treatment, as I will try to demonstrate here below.

During several decades the architectural landscape of the Ruhr Valley towns in Germany has been dominated by neglected brown fields, industrial ruins and run-down postwar buildings. That is now becoming a thing of the past as architects from all over Europe complete their projects in the former coal-mining region.

The ThyssenKrupp Quarter in Essen is part of a 230-hectare downtown area known as the Krupp belt. The site, kept for years as a wasteland, is a historic place. In 1818, Friedrich Krupp founded a cast steelworks on the same spot, which his son Alfred turned into a global company. Railway tracks were produced here for the United States, and less exciting but quite effective canons were casted in the area for two world wars. It is a place in German history that triggers mixed emotions to say the least. A less known but more interesting tip for architects: the huge 'gerberettes' designed by Rice, Piano and Rogers for the Pompidou Centre in Paris were also built at the Krupp furnaces, not far from Essen. Krupp was the only company in Europe who stood to the challenge of producing the big cast steel pieces that were to play a significant role in the structural concept of the Beaubourg.

ThyssenKrupp has built its new headquarters in this historic part of Essen at a total cost of 300 million euros. The technology giant, which employs 173,000 personnel in 80 countries, has no interest for skyscrapers. ThyssenKrupp’s chief expectation during the competition was that architects made the essence of its brand visible: transparency, innovation and far-ranging versatility. With the bulk of the masterplan finished this last summer, corporate culture and German industrial power welcome a new symbol.

Chaix & Morel et associés (Paris) and JSWD Architects (Cologne) won the competition for the campus buildings and developed the ThyssenKrupp Quarter for a working population of 2,000 employees. There is ample space for them here. A 200 meter-long and 30 meter-wide pool forms an axis along which various buildings and generously laid-out boulevards appear. It is quiet around here, too. Cars disappear into car parks and subterranean garages around the plot. All deliveries are conducted below ground. Above this, 68 trees from five continents form a boulevard. There are large expanses of lush green lawn without bushes or perennials. The important aspects here are distance, silence and solemnity. Peter Drucker would have salivated in awe: this is the spirit of the new corporation, built to last.

The main building, known as Q1 and officially inaugurated in June, has a flexible facade layer made up of 400,000 stainless steel slats. This system aims to make air conditioning redundant. A weather station on the roof sends signals to a computer that steers the rotation of the facade slats. The design makes use of the material Nirosta, one of the concern’s branded products. ThyssenKrupp also aims to improve the cladding of high-rise buildings, and replace expensive aluminum profiles. To this end, the company has developed steel sheeting with a zinc and magnesium coating.

There are three elements that deserve to be described in more detail in this post: the glass mullionless curtain walls in the centre of Q1, the sunshades at the external office areas also in Q1, and the flat-rolled steel cladding of buildings Q1 (inside the atrium), Q2 forum, Q5 and Q7 (as the main facade cladding). Let's go with the description, one at a time.

Panoramic windows at the atrium
The large atrium area of Q1 shimmers as a result of its pearl-metallic gold color internal cladding. But it is primarily the expansive volume of space that captivates. The 50 meter-high building, bonded from two L-shaped structures, is dominated by 'panorama windows', in fact two large tensed cable curtain walls. Both glass constructions are 28 meter high and 26 meter wide. The design and engineering of the panorama windows was done by Werner Sobek from Stuttgart. The facade contractor was Hefi Glaskonstructiv from Talheim, Germany.

View of the main axis pool through the panorama window at Q1

A steel pre-stressed cable net system holds the individual glass panes in place. Each double glass unit is 2.15m wide x 3.60m high, with clamps at the corners and mid height to connect it to the vertical and horizontal steel cables. Pre-stressing in two axes made it possible to eliminate complicated transitional details to the adjacent facade structures. In the vertical direction, with a grid dimension of 2.15m, the grid is composed of pairs of pre-stressed cables with a diameter of 30mm each. They are fixed to a three-story steel truss below the building’s 11th floor. The horizontal net structure, attached at the ends to the story floors, consists of one pre-stressed steel cable every 3.60m, with a diameter of 32mm. The vertical cable disposition in pairs allows the transfer of the glass self-weight via a force couple - tension and compression - into the pre-stressed cables. The horizontal pre-stress per story is 34 tons, while the vertical pre-stress connection is 2 x 15 tons. To transmit these forces the engineers from Werner Sobek chose carbon steel of grade S355. Compared with stainless steel, carbon steel displays a higher strength and a lower thermal expansion. The cables have a tensile strength of 1770N/mm2.

The structural solution followed here is quite similar to the Lufthansa Aviation Centre in Frankfurt, also by Werner Sobek, although in Frankfurt the only load-bearing elements are the vertically tensioned cables.

Atrium with panorama window to the left

The choice of glass was critical too: on the one hand it had to have solar control, while on the other it had to be clear with as little tinting as possible. To achieve the aim of maximum-possible transparency, a custom solution featuring insulated clear glass panes was selected. The structure is as follows: a) 12mm single-pane safety glass, b) 16mm inter-pane space, c) 2 x 8mm laminated safety glass with 1.52mm PVB film for solar control. The type of glazing chosen and the reduced support structure have resulted in an only 45 mm thick membrane that appears completely dematerialized. Despite being so thin, the glazed membrane met all thermal insulation requirements. I have not found any reference to argon fill in the glass cavity, but assume it is the case or the U-value would have been too high.

The images below show the section, elevation and concept details of the glass fixings.

ThyssenKrupp Q1 building: vertical section and panorama window glass elevation

ThyssenKrupp Q1 building: vertical detail of fixing at glass crossing. Two cables run vertical, one cable (sectioned) runs horizontal. All screw heads are embedded on the cast steel piece.

ThyssenKrupp Q1 building: horizontal detail of fixing at glass crossing, and elevation detail of the external clamp. Two cables run vertical (sectioned), one cable runs horizontal.

The panorama windows viewed from inside

It’s not just the two panoramic windows that contribute to the amount of light that floods the atrium: there is also a large window opening in the atrium roof, supported by a cable net. Its dual-curved outer skin measures approximately 21 x 21m.

The technology of pre-stressed cable net facades is not new, and it's a very German one. If you are interested, there is a good summary in pages 235 to 243 of the highly recommended thesis by Mic Patterson, 'Structural glass facades: a unique building technology'. The first and still best known example of this glass wall system is the lobby of the Kempinski Hotel at the Munich airport, designed by Helmut Jahn and engineered by Schlaich, Bergemann & Parters. The hotel lobby was completed in 1993 and still looks amazing 17 years afterwards. The cable net grid in Munich is much smaller than the one in Essen, but there is only one cable per direction, making the knots less visually imposing than those of the ThyssenKrupp atrium. One could say that the Sobek version is more imposing in size and less innovative in the fixing details than its SBP's counterpart. But Munich was a much less rigid, monolithic glass, not an insulated screen. In any case, at least to me, the real interest of Q1 does not lay on the panorama windows, but on a much humbler element: the sunshades of the office space all around the building.

Sun-shading movable slats
Our industry has been strongly discussing for some years about the energy irrelevance of double skin glass facades. Their former advantage in reducing U-values has been equaled by the triple-glass units with argon-filled cavities and high-performant coatings developed in the last decade. On the other hand, g-value or heat gain coefficient (the % of solar radiation that penetrates through the glass) remains as a serious problem for office buildings in summer period. Renzo Piano was the first one in introducing the 'mediterranean double skin', that is, a continuous glass facade with a set of sunshades on the outside for solar protection. An energy simulation study presented by Mikkel Kragh and Annalisa Simonella from Arup Facade Engineering at ICBEST 2007 has got to the same conclussion: there is no direct correlation between U-value and overall energy performance in a building with high internal heat gains, as an office building. In other words, the main driver is exposure to solar radiation.

The best answer from a energy and daylight perspective, even in a cold climate as the Ruhr Valley, is to combine a lowish Uw-value (around 1,2W/m2ºK for example, achievable with double glass units and high-performant thermally broken profiles) with an effective sunscreen. 'Effective' here means a screen that reduces solar gains when there is direct solar radiation but lets daylight in when there isn't. That is, a moveable sunscreen. Et voilà: this is the solution applied to ThyssenKrupp Q1 facades.

Multiple image with fins at different angles from 0º to 90º

The sun-shading concept was suggested by the architects and developed by the Fraunhofer Institute for Solar Energy Systems in Freiburg. The energy study came out with a proposal to provide a constant horizontal overhang - useful for summer protection and as a catwalk - combined with a vertical set of twisting fins. The fins would twist to achieve an adjustable position between 0º (parallel to the facade: total direct radiation blocking) and 90º (perpendicular to the facade: maximum daylight penetration).

The great idea in this concept was to create a vertical fin made of horizontal cantilevered slats that were connected to a central stud, something similar to vertebrae in a spine. The cantilevered fins at each side of the stud can twist independently, as arms that rotate from widely open (0º) to parallel and intertwinned (90º). The final touch was to provide a shape for the fins that was non-rectangular, thus creating an interesting texture as the fins rotate along the day.
The sunshade elements have been manufactured by ThyssenKrupp Nirosta (the company branch for stainless steel) using a chromium- nickel-molybdenum stainless steel with high corrosion resistance called Nirosta 4404 (that is, EN 1.4404, equivalent to AISI 316L).

The movable fins from inside, with the horizontal catwalk

Each slat is ground on one side and sandblasted on the other. The slats thus appear to be matt or glossy depending on the point of view and incidence of light. The slat surface directs the incoming light indoors in such a way that the offices remain bright enough even if the sun protection is closed.

The manufacturing of the sun protection system must have been demanding. First, the metal strips were processed by ThyssenKrupp Umformtechnik, the group's automotive manufacturing unit. Then, Frener & Reifer, the facade contractor from South Tyrol mounted 116 to 160 slats onto each axis to form electrically driven slat packages. In the process, it was important that the slats remain movable in the center axis and react precisely to the signals of the electrical drive. It's funny that Frener & Reifer motto is 'Starting where others stop', completely adequate to this particular job. The facade contractors did also install the inner curtain wall, made with Schüco elements. Both skins in Q1, curtain wall and fins, are approximately 7,800m2 each.

The virtual animation at the Frener & Reifer page shows the movement game better than my words. The programming is really sensitive: the control system not only detects the seasonal sun position, but also knows what the current weather is like due to the data of a weather station located on the roof of Q1 building. On cloudy days, for example, all the slats will be turned outwards so that the sun shades remain open. Even when the slats are closed directly in front of the facade, employees can open the windows and access for maintenance is always possible.

There are in total a number of 1,600 motors to activate the fins movement. This seems as a maintenance nightmare, but it doesn't have to be so. Movable facade elements are more and more common lately, with motor costs going down and system reliability moving up every year.

This is a revolutionary design move, not in concept but in results: I suspect we will see many more moveable sun-shades in the near future. There is an interesting joint venture between Buro Happold and Hoberman, called Adaptative Building Initiative, that provides nothing but moveable facade elements to control solar gains and light levels at the same time.

External steel cladding

Sheet metal has long been considered a second rate cladding material – an impression the buildings of the ThyssenKrupp Quarter had to change. The final image of the buildings around Q1, finely glimmering in a champagne hue of metallic elements, consist of nothing other than sheets of steel.

ThyssenKrupp Quarter, Q2 Forum building facade clad in coil coated steel sheets.

Not just any sheet steel but a high-quality, fine sheet steel organically refined using a coil coating method. Fine sheet metal, coated using the hot-dip method, can be shaped, welded and painted. The 3m long and 0.67m wide, chamfered steel panels of the Quarter are resistant to wind, weather and UV radiation. Here, one percent of magnesium is added to the molten zinc for the fine sheet metal. As a result, improved corrosion protection is achieved with a thinner coating, which means that the valuable raw material zinc can be used sparingly.

Q2 Forum facade mock-up on site

The fine sheet metal, with a thickness of 0.8 to 1.2mm, is more affordable than a comparable facade element made of aluminum sheets of 3mm, at least so the ThyssenKrupp guys say. The material is called PLADUR ZM Premium steel; used as cladding for the walls of the atrium inside Q1, the interior of the ground-floor lobbies in Q2, Q5 and Q7 buildings, and the exterior facade areas on Q2 forum, Q5 and Q7. The material owes its appearance to a multi-layer coating in a color named Pearl Metallic Gold. Thanks to special pigments, the color shade of the surface changes depending on light conditions and the angle from which it is viewed. The term “Premium” refers mainly to the quality of the top coat, while the abbreviation ZM means that the surface of the steel is first protected against corrosion with a zinc-magnesium alloy coating before the paint system is applied. This alloy provides roughly twice the corrosion protection effect of conventional hot-dip galvanizing.

TKQ, Q5 and Q7 facades

It's fair to record that the façade area consultant for the Quarter has been Priedemann Fassadenberatung from Berlin. No information can be found at their Webpage about the project or their contribution though.

Let me finish this long post in silence. No more words - there have been too many! Just some selected images of Q1 and the sun-shading slats that struck me when I first knew about this project. In awe...

Building up the perfect wall

2010-11-28T18:06:00.003+01:00

There are dozens of facade consultants, facade engineers or building envelope specialists Webpages out there. Many of them are being listed in this blog, in the column Engineers & Facade consultants. There is a constant in these pages: you won't find almost any information about what we facade specialists really do for a living. We don't write there. We have no opinions about our field of experience. We seem to be on the hyperspace trying to convince potential clients that we are the right folks for them, just because our Webpage - not designed by us - looks great or professional. The fact that it almost always looks boring doesn't seem to bother us.

There is one exception at least, one that clearly jumps above all others. This post is dedicated to a bunch of building science specialists - mainly building envelope related - who are brave enough to write and say what they think and do. Their Webpage is called Buildingscience.com. Against all odds, it's not another governmental agency or something paid by a guild of construction materials suppliers. Building Science Corporation is a firm of building consultants and architects, located in Massachusetts with a branch in Ontario. They specialize in building technology consulting, more specifically in preventing and resolving problems related to building design, construction and - yes - operation. They seem to be experts in energy efficiency, buildings retrofit, moisture dynamics, indoor air quality and building failure investigations.

The difference between this team and other building envelope specialists is the people they have and the way they market themselves. Two of the principals, Joseph Lstiburek and John Straube, are also the most active writers of articles in the information part of the Webpage. These guys sum up a huge field experience with strong academic and research roots, combine knowledge with an entertaining writing style, and deal with issues one rarely finds treated with such clarity. Lstiburek founded the company, Straube joined later. Lstiburek seems to be the one with practical roots, reinforced by being part of the 'Building America' program at the US Department of Energy. Straube seems to be the professor in the team, teaching building science in the Civil Engineering Department and School of Architecture at the University of Waterloo, Canada.

There are several document files available at their Webpage. The most interesting papers can be found under the labels Building Science Digests (BSD), Building Science Insights (BSI), Guides and Manuals (GM) and Research Reports (RR). There is also a complete Glossary of Building Science terms. Digests and Insights are much less dense and really fun to read. Let's have a look for instance at BSI 005: A bridge too far by Joseph Lstiburek. The topic is obviously thermal bridges. You can find sentences as these:

For a bunch of supposedly clever folks we sure do dumb things. One of the big ideas of the past couple of decades or so is to keep the heat out during cooling and keep the heat in during heating. The better we are at this the less energy we need to use to condition the interior. Apparently this concept has not caught on. (...) If an alien from another planet looked at our construction practices he would conclude that we have too much heat in buildings and we want to reject that heat to the outside.

The paper is illustrated with images as clear as the one below (the caption has been copied from the original):

"Clint Eastwood" Thermodynamics—“The Good” uses offsets and exterior insulation. “The Bad” only uses exterior insulation. “The Ugly” uses neither.

Why can't we be as clear as these folks when discussing about things we all know - and can be measured?

Let's go back to the paper that bears the name of this post, BSI 001: The perfect wall, another example of must read building envelope science. The author is again our entertaining but precise Joseph Lstiburek:

The perfect wall is an environmental separator—it has to keep the outside out and the inside in. (...) Today walls need four principal control layers—especially if we don’t build out of rocks. They are presented in order of importance: a) a rain control layer, b) an air control layer, c) a vapor control layer, and d) a thermal control layer.

In concept the perfect wall (see image to the left) should have the rainwater control layer, the air control layer, the vapor control layer and the thermal control layer on the exterior of the structure. The cladding function is principally to act a an ultra-violet screen and a first rain screen. And yes, architects also consider the aesthetics of the cladding to be important.

At this point Straube goes for a second to Canada, and refers (without mentioning their names) to the seminal works of the Norwegian O. Birkeland and the Canadian G.K. Garden about the concept of rain screen cladding and the control of rain penetration. I will dedicate a post to these guys and their papers, written in the first half of the 60s, since their influence is greater today than at the time of writing. Another old Canadian professor is cited here, N.B. Hutcheon, whose Principles Applied to an Insulated Masonry Wall (1964) are also completely up to date. The images shown here below, taken from Hutcheon, still resonate in their clarity.

It is interesting to follow Hutcheon's reasoning when he compares these two sections 46 years ago:

Wall to the left is representative of a number of current designs that have been used quite extensively in recent buildings. It is of a basic form consisting of 8-in. back-up and 4-in. facing, in this case stone, which has been widely used in Canada over the past 50 years or more. Insulation is now commonly added to the inside, and may take several forms including mineral wool between strapping or foamed plastic serving also as plaster base. Full mortar backing, which usually requires a very wet mortar, is commonly used behind the stone.

(...) Reference to the winter temperature gradients for Wall to the left will show that all material outside the insulation will fall below freezing. (...) Rain penetration through cracks, occurring as a result of temperature movement in the exterior cladding, can also allow the entry of water and the wetting of the wall.

A dramatic difference in temperature conditions and their attendant dimensional changes can be effected by moving the location of the insulation, see Wall to the right. The main wythe and all the parts of the structure in contact with it are subjected to a much smaller range of temperatures. The possibility of disruptive dimensional changes arising from temperature effects is greatly reduced for all but the exterior cladding and, as will be discussed, these can readily be accommodated. The window frame, now bedded in or fastened to the warm interior wythe, is relieved of the substantial edge-cooling effect of the former arrangement. Advantage can be taken of the inside metal sill to collect and conduct heat to the frame, and a thermal break may be incorporated on the outside to minimize the loss of heat in winter.

(...) The exterior cladding can be arranged as shown for Wall to the right in the form of an open rain screen. It may be set out to form an air space and supported by ledger angles and ties as before. The air space, being heavily vented by suitably designed open joints at both horizontal and vertical intervals, will at all times follow closely the outside air pressure so that the rain screen is substantially relieved of wind pressure differences. This not only removes the major force causing rain to penetrate the cladding, but also eliminates the wind loads on it.

Isn't it amazing? We are still - 46 years later - teaching this exact lesson to new generations of equally astonished architects. Even worse, we still see in 2010 a number of projects with wall sections similar to the left detail instead of to the right one. Lstibureck goes one step further in his paper to discuss the preferred position not just of the thermal barrier, but of the four control barriers as he calls them: rain, air, vapor and thermal. The details are clear in his article. I will summarize here one of the conclussions because it is of great help for us to do a good detail of any building envelope - be it a wall, a roof or a slab in contact with the earth.

Lstiburek describes first the roof adequate build-up (image above to the left) and then the slab in contact with the earth (image to the right), to find out a striking similarity between those two and with a perfect vertical wall:

The perfect roof is sometime referred to as an “inverted roof” since the rainwater control layer is under the insulation and ballast (i.e. roof cladding). Personally I don’t view it as inverted. Those other folks got it wrong by locating the membrane exposed on the top of the insulation—it is they that are inverted. The perfect slab has a stone layer that separates it from the earth that acts as a capillary break and a ground water control layer. This stone layer should be drained and vented to the atmosphere— just as you would drain and vent a wall cladding.

Notice that in the perfect roof assembly the critical control layer - the membrane for rainwater control, air control and vapor control is located under the thermal insulation layer and the stone ballast (i.e. “roof cladding”) so that it is protected from the principle damage functions of water, heat and ultra violet radiation.

What happens where roofs meet walls?. The classic roof-wall intersection is presented in the figure to the left. Notice that the control layer for rain on the roof is connected to the control layer for rain on the wall, the control layer for air on the roof is connected to the control layer for air on the wall . . . and so it goes. Beautiful. And when it is not so…ugly.

In a beautiful bit of elegance and symmetry if you lie the perfect wall down you get the perfect roof and then when you flip it the other way you get the perfect slab. The physics of walls, roofs and slabs are pretty much the same—no surprise.

This insight was shown into a whole generation of practitioners by the good building envelope specialists since back in the sixties. Where? Our friend Lstiburek is proud to have got it at the University around the eighties - he is a mechanical engineer. Others can not be that lucky: I found this piece of information by myself after finishing my architectural studies. It doesn't matter when - what matters is that, once you get it, you should never again forget it. Articles as clear as this one remind us this lesson. And there are many others at the Webpage... so please, go there and have a look, for your own benefit.

Large glass installation: miracles of vacuum lifting

2010-11-26T18:50:00.007+01:00

The cladding world has gone mad. Facade units get bigger and bigger every year. Glass and panel dimensions are exceeding any reasonable measure. Who are to be blamed for it? Architects are partly responsible, for sure. The last gossip says Foster + Partners are designing a big company HQ in the Pacific coast with 15m long insulated glass units. Seismic movements in the region don't seem to refrain the architects from trying the impossible once again...

Henze-Glas DGU in the factory, before shipping to Glasstec 2010. 35 chaps are sitting on top of the 18m long glass unit

The monster DGU unit as shown at Glasstec 2010

But industry has also entered the race with pleasure. The 'jumbo size' glass, that is, the maximum dimensions of a glass sheet, was 6,000 x 3,210mm up to 2007. Since then a new jumbo size appeared: 9,000 x 3,210mm. Double glass units of 7,500 x 3,200mm or even 9,000 x 3200mm are now commercially avilable. Visitors at the last Glasstec Düsseldorf in October 2010 could see a huge insulated glass panel of 18,000 x 3,300mm! It had three layers of 10mm and weighed 4,5 tons. The producer was the large-dimensions glass specialist Henze-Glas from Hörden, Germany.

The Henze-Glas guys usually take care of the fabrication and supply of their glass units to jobsite, all in one, since large dimensions are not easy to handle. But the tricky question is: how can a facade contractor install glass or metal panel units around 10m long in a facade? This is the issue we are going to discuss in this post.

Mankind has been aware of the power of air pressure since Otto von Guericke’s demonstration of the Magdeburg hemisferes in 1656, when 16 horses were unable to separate two hemispheres which had been pumped free of oxygen. Boyle and Hooke, two good old names of physics, worked together to design and build an improved air pump. Their work was the origin of the Boyle's law: the volume of a gas body is inversely proportional to its pressure.

Early Wood's Powr Grip cups, beginning of 1960's

It wasn’t until the 1960s that air pressure power started to be used with vacuum lifting equipment for transporting and installing glass panels at construction sites. One of the founders of the guild was Howard Wood, who in 1961 designed and built the first Wood's Powr-Grip Valve Grinder. The tool consisted of a small, spring-action vacuum pump mounted in a wooden handle, opposite a rubber suction cup which attached to the flat surface of an engine valve. The demand for the unique little lifting tool grew, and a glazier friend from Wood's suggested that he develop a vacuum cup for handling glass. With support from friends, Howard began manufacturing vacuum cups for glass handling in 1963, and obtained a patent for his design in March 1966.

Hydraulica 2000 vacuum lifter

Vacuum cups were soon attached to cranes or lifting devices, and soon a new machine came into play: vacuum lifters. The generally smooth and gas-tight surface of glass means vacuum lifting devices are just right for the job. That is also the case with metal panels. These days even stone and prefab concrete panels are lifted and moved using air suckers.

Vacuum lift atached to a crane from Anver

Wirth GmbH is a German company that builds applications for vacuum lifting. The first version of their Oktopus lifter appeared in 1992. With devices like that installing large-format roofing, ceiling and facade panels made of sandwich, profiled sheets and glass has become much easier. Today's vacuum lifting equipment is based on individual suction cups attached to thin structural elements hung from a crane. These systems allow for the installation of vertical wall panels up to 12m long, or even horizontal roof panels up to 22m long.

The lifting devices can be hung from a crane, attached to a forklift, to a truck-mounted crane or to an elevated working platform - also known as cherry picker. Several hydraulic functions integrated into the vacuum lifters allow panels to swing up and down, be raised and lowered, twist left and right, or move forward and backward horizontally.

One of the best options is to use a vacuum lifter attached to a minicrane, also called a spider crane. Two European companies are well-known builders of minicranes: Unic Cranes from Scotland and Riebsamen from Germany, the latter being better known for their brand Glasboy. These minicranes can be used for mounting curtain wall units from the floor above, or for mounting glass in a skylight from the atrium below. The dimensions of a minicrane when its legs and arm are folded are really minimal, allowing the smallest minicranes to be lifted inside an elevator.

Minicrane Glasboy Frey 860 from Riebsamen

Some special devices can solve typical installation problems. One of them is the presence of overhangs in high level installation works. If a cantilevered slab prevents cranes from lowering their load flush with the envelope, an overhang beam provides an ingenious way of overcoming the problem. The Libro 500 overhang beam for example provides a reach from suspension point to pad extension that allows glazing under overhangs up to a depth of 1,750mm.

All the options of cranes, minicranes and vacuum lifting devices can be checked (and hired, if you need them) at the UK webpage of GGR Group, a must see for those with a lifting problem to solve. If your site is in the US, then go visit the founding fathers, the guys of Wood's Powr Grip. If your doubts are more general or you want to have an overview of the crane and lifting world, have a look at Vertikal magazine.

Now, let us enter a slightly tougher issue. Which lifting device do I need for my load? How many suction cups are required considering the glass dimensions? Is suction lifting really safe? Depending on the application and the device, the load bearing capacity of a vacuum lifter varies between 250 kg and 1,000 kg. Vacuum lifting devices suitable for construction sites must be battery powered and therefore completely self-sufficient. A safety system inside the device constantly monitors the condition of the vacuum circuit and the batteries. Optical and acoustic warning signals give early indication of deviations from the normal conditions. A reserve vacuum system maintains load bearing capacities even in the event of a loss of power, so that there is enough time to safely deposit the load once an alarm goes off.

Robotic (left) and Libro 500 overhang crane lifts

European norm EN 13155 defines how to verify the load bearing capacity of vacuum lifting equipment. Load bearing parts are to be checked at three times the nominal load bearing capacity of the device. Vacuum lifters must be able to hold a load, in all positions at the end of the vacuum range, of at least two times the nominal load bearing capacity of the device. The combination of vacuum lifting device and suctioned load must, obviously, not exceed the load bearing capacity of the lifting equipment (crane / forklift / working platform). If you are interested in the same topic from the US, your document should be ASME Standard B30.20, addressing vacuum lifting and general materials handling products.

The load bearing capacity of the suction cups depends mainly on the following four factors: a) Size of the suction cups; b) Pressure difference between the level of vacuum in the suction cup and the ambient pressure; c) Load direction (vertical, parallel or sloped to the suction cup surface); and d) Surface properties and porosity of the suctioned material.

As a rule of thumb, a vacuum lifter used at a height of 1000m admits 10% less weight than the same device at sea level. The load direction is even more critical. If the load to be lifted is picked and released in a horizontal position, the maximum load capacity will be two times higher than if the load has be hold in vertical. Finally, the suction cup diametre defines the load bearing capacity of the system. The chart below, taken from Wirth Webpage, shows the relationship between suction cup diametre and load bearing at sea level for both horizontal (blue line) and vertical (red line) load directions.

We started this post talking about large glass units. The vacuum lifters you can find in the market have a maximum load bearing capacity of 1 metric ton at best. What if your glass is really large - and heavy? No problem, there is always a German wizard with a solution for that - regardless the names they give to their inventions. Bystronic Glass has built the world's largest glass vacuum lifter up to now: the Glasmaxilift 5000 is able to handle glass lites up to 15 meters in length and 5 metric tons using just air pressure. You got it. And Foster + Partners will have their huge glass installed as well.

Will transparent polymers kill glass?

2010-11-14T09:09:00.208+01:00

A silent revolution is taking place these days. Due to a number of reasons, the glass position as the one and only transparent filling for curtain walls is being threatened. Who is the new kid on the block? Well, it has been around for a while, but it has grown bigger now: transparent recyclable polymers, commonly called thermoplastics.

Tokyo glass and acrylic cantilevered structure, Dewhurst Macfarlane

The attack of the polymers has already started, in the way barbarians entered the Roman empire: as an alliance. If you need a good bullet resistant glass you will end up in a laminate called glass-clad polycarbonate. Beware: the higher the bullet resistance requirements, the less glass there will be in the laminate. If you are after a blast-resistant curtain wall, the options are heavy PVB laminated glass (1.52mm or more of polyvinyl butiral layers) or glass combined with an ionoplastic interlayer as SetryGlas, in widths of 2.28mm or more. If you want to have overhead glazing or horizontal glass with live loads, there you will find the plastic companions again. Structural glass is in fashion, and you may want to achieve all-glass, non metal-supported transparent structures. When you do that, most of the time it's due to the help of polycarbonate sheets glued to the glass with transparent polyurethane interlayers.

Tokyo International Forum, glass canopy details. PMMA was not required structurally but it was added as a safety measure against typhoons and earthquakes.

This was the situation up to now. Glass is still in complete command if we want to clad a facade with a transparent, low U-value, durable and non combustible material. A curtain wall is still synonym for a glass curtain wall. But things are starting to change, and the big polymers suppliers have focused their attention onto the new frontier: to introduce Transparent Composite Facades (TCF) in lieu of Glass Curtain Walls (GCW).

I have taken the TCF name from a PhD dissertation in the University of Michigan, submitted by Kyoung-Hee Kim in 2009, and advised by Professor Harry Giles. The title is Structural evaluation and life cycle assessment of a Transparent Composite Facade system. I have also got ideas for this post from a presentation at the last Glasstec conference in Sept 2010: New materials for transparent constructions, by Eckhardt and Stahl.

Prism Cultural Centre in West Hollywood, California by PATTERN Architects. Translucent facade in resin-based composite polycarbonate. 3Form, an advanced material fabrication company specializing on resin-based composites, has collaborated on the facade solution.

The contenders to take the place of glass in curtain walls are four thermoplastics: polycarbonate (PC), polymethylmethacrylate (PMMA or acrylic), polyethylene terephthalate (PET or nylon) and polypropylene (PP). PET and PP are still lagging behind in the race, mostly because of their low stiffness and low ultimate strength. PET and PP have a Young's modulus 1/7 and 1/2 that of polycarbonate and acrylic, and their ultimate strenght is 1/3 that of polycarbonate and acrylic. The main advantages of polycarbonate and acrylic, on the other hand, is that they are 20 times less brittle than glass and their ultimate streght can be two times higher than glass (see data on the table below). So, we will focus on polycarbonate and PMMA / acrylic from now on.

From 'Materials and design' by Ashby and Johnson, plus www.matweb.com

Some may say these two materials have been around for too long to worry about them now. That is true, but doesn't tell the whole story. Let's call them by their best-known brands: polycarbonate is better known as Lexan, Makrolon or Danpalon. PMMA / acrylic is sold under the brands Plexiglas, Lucite or Perspex. Polycarbonate, either in solid or in multilayered sheets, has found a safe place in architecture as a translucent wall cladding, not transparent. A great example is the Laban Dance Centre in Southern London, a proyect by the Swiss architects Herzog & de Meuron with PC sheets supplied by Rodeca in Germany.

Laban Contemporary Dance Centre, London. Herzog & de Meuron architects

The cladding on the Laban Centre has four layers with a U-value of 1.45 W/m2°K, better than a low-e double glass unit. But present multiwall polycarbonate sheets, only 60mm thick, have already reduced the U-value to 0.85W/m2ºK, in the range of a triple glass with argon and low-e coatings. Polycarbonate can also reduce reliance on secondary solar control; the panels used at the Laban Centre feature dimpled inner skins that diffuse the light. Concerns over the durability and UV resistance of polycarbonate have now been reduced thanks to new film protection technology. Manufacturers now guarantee that the polycarbonate will lose no more than 1% of its transparency over the first 10 years. All this is fine, but this is still a translucent wall, a cladding material for gyms, dance centres, swimming pools or industrial buildings.

V-profile by Rodeca, a mullion in extruded polycarbonate

The next step for solid polycarbonate and acrylic is to become the transparent filling of a curtain wall, both in the fix elements and in the windows. A transparent composite facade (TCF) is well described by Kyoung-Hee Kim's dissertation as:

A composite construction consisting of a polymer double skin with an inner composite core, configured to provide a stiffer, safer, energy efficient and lightweight alterative to a glass façade system.
This new 'glazing' system has spurred studies that evaluate the material performance of polymer and composites as a cladding material. The polymer skin has a sustainable characteristic due to its recyclability, which can help to reduce the environmental impact associated with raw material depletion and disposal.

Let's use an existing example to visualize the new TCF coming. Kalwall is a well known US translucent facade and skylight system, whose filling material by the way is a thermo-set polymer reinforced with fiberglass, with modified properties regarding UV-resistance and reaction to fire. The basic panel comes in standard dimensions and is installed as a very simple curtain wall unit sistem.

City & Islington College, London. Van Heyningen and Haward architects. Kalwall and glass facade.

The best version of Kalwall, pushed by Stoakes (the UK distributor) to comply with EU directives, has really low U-values by using thermally broken profiles combined with aerogel insulation. Even without aerogels you can have a 100mm panel, filled with polycarbonate fibres, with a U-value of 0.83W/m2ºK and a solar factor of 0.15. But, alas, it's still translucent. Now, imagine you replace the fiberglass reinforced thermoset at both sides of the panel with a high resistant solid policarbonate sheet, and add some intermediate transparent sheets to improve its U-value and acoustic performance. The outcome would be something similar to Kalwall - with the same Japanese paper-like rectangular pattern - but wholly transparent, no glass required whatsoever. Stop imagining, this concept is already being developed somewhere in Europe.

If we move to PMMA / acrylic, a similar story is being written these days. The material can be easily molded to achieve fuzzy shapes at a cost which is only a fraction of glass. In solid state, acrylic sheets can be cut and mechanized using laser cut CNC machines to provide extrusion-like profiles. A great example is the facade of the Reiss HQ building in London by Squire and Partners architects, with a machined PMMA external skin, and lit with an LED system at the bottom of each floor level.

Reiss London. Double skin facade with acrylic and glass.

Reiss London. Acrylic milling process and finished facade panel.

Evonik Röhm, the company that owns the Plexiglas brand, was founded by Mr Röhm, the inventor of PMMA in 1933. After almost 40 years, the Olympic stadium in Munich by Frei Otto is still a forward-looking piece of architecture. The complex grid of steel cables was clad with a solid, tinted Plexiglas sheet to provide shelter against the summer sun rays. Need versatility? The monolithic thickness of PMMA is 200mm in a dimension of 3 x 8m - larger than glass, and you can even weld acrylic with hidden joints for bigger units. In the extrusion process you can obtain 25mm thickness, a width of 2m and no limit with length.

Olympic Stadium, Munich 1972. Frei Otto and Günther Behnish.

Curving a polymer is easy, but equally so is molding. Transparent facades as the one at the Liquid Wall in Berlin, the flagship store of Raab Karcher, would be a nightmare in glass, but are feasible in acrylic. Home Couture Berlin is a showroom for tiles and spa accessories. The store provides an ideal presentation platform for Raab Karcher and its joint-venture partners from the premium tile and bathroom fittings sector. The store functions as an elongated shop window for passers-by.

Raab Karcher flagship store, Berlin

The ‘liquid wall’ installation of milled Plexiglas appears as a vertical wall of water and serves as an eye-catcher in the Ku'Damm facade. The distorting lens makes the illuminated back wall oscillate as you wander past it. The shop window has been made after a 50mm Plexiglas sheet milled, formed and polished to get convex and concave surfaces. This form creates an effect of a moving room while walking by the window, as if the inside were a swimming pool.

If you need more inspiration, have a look at these four polymer materials suppliers: 3form, Panelite, Lightblocks and Krystaclear. These are all US-based companies at the verge of another revolution: they are not just suppliers, but also fabricators, engineers, materials researchers and high-end designers. They are in the front of the 'design to manufacture' concept that is changing the way materials are used. And they are all based in polymers.

When you can't win your enemies, join them. Another interesting product is Gewe-composite by the German glass supplier Schollglas. This laminated safety glass made with two sheets of glass and an intermediate 2mm polymeric membrane, can replace thicker glass-PVB laminates, is very easy to cold bend and does not stop UV radiation, thus making it very appropriate for winter gardens. The Amazonienhaus botanical greenhouse in Stuttgart is a good example of high UV-transmission, low-e coating composite transparent cladding. Another striking use of this composite in a bent application - non heat mold required - is the Mobile Formula 1 Event Centre for McLaren in the UK. The cold bent composite here integrates metal sheets and comes with a highly selective coating.

Amazonienhaus Stuttgart. Glass laminated panels with high UV transmission from Schollglas

Gewe-composite from Schollglas

There are still issues to solve and improve with thermoplastics before they can replace glass in curtain walls. Even if their mechanical properties are OK in general (impact resistance being great in particular) long term creep deformation is a clear disadvantage. The elastic modulus of extruded polycarbonate, for example, can be reduced to 40% after 1000 hours of constant loading. Regarding durability, polymers and acrylics offer a lower durability and weatherability under outside exposure compared to glass. Coated protections against UV have improved this, but there is still a way to go. The yelowness index (YI) measures discoloration levels under UV exposure, and values above YI-8 are not recommended for external use.

Another issue that must be integrated in the design is the thermal movement of plastics. The coefficient of thermal expansion of both polycarbonate and PMMA is 6 to 7 times greater than that of glass. Beware of the expansion pockets and frame movements! Abrasion resistance of plastics has improved with external coatings, but its value is still 2 to 4 times lower than that of glass. The biggest issue with plastics as external facade elements is probably their flammability or fire reaction. On one side, PC, PMMA and glass all conform to the flammability requirements of the ASTM codes. However, full compliance with the International Building Code (IBC) has to be checked case by case. The IBC limits the installation of plastic glazing to a maximum area of 50% of a building facade.

It is interesting to note that the U-value of a single layer of 6mm of transparent glass, polycarbonate or acrylic is practically the same: between 5,2 and 5,8W/m2ºK (glass being the highest). We get a similar result with g-value and light transmittance: uncoated glass and polycarbonate transmit the same amount of solar and visible radiation, while acrylic is slightly more transparent in both cases. But when we introduce selective coatings, glass performs much better than plastics in energy and visible light terms. Up to now, though.

Nobody knows the end of this story. Will new recyclable polymers completely replace glass as a transparent filling for curtain walls? It seems uncertain, but at least I would vote for a future co-habitation of both materials. If I had money to invest in the stock market, I would buy plastic shares rather than Saint Gobain ones. Well, don't follow my advice too quickly: Saint Gobain is investing in plastics right now, so think twice...

Central Saint Giles: Piano goes to London

2010-11-08T16:43:00.123+01:00

Central Saint Giles, a London commercial and housing scheme designed by Renzo Piano, has been attracting attention ever since its glazed ceramic facades in tiles of red, orange, yellow, green and grey began to appear back in 2009. Now, with the complex finished after Spring 2010 and starting to be occupied, it is time to review its facade design and construction.

Renzo Piano is a master for many of us. This building, nevertheless, has not attracted unanimous praise as usual. I think the reason is the difficulty underlying the task: difficulty because of the site, the density, the scale and the neighbourhood. Through this post I hope to present the lesson Piano has given to all of us: a lesson of working under difficult conditions and still come up with a victory. This may not be a victory for a building as a piece in itself, but a victory for a building that improves the city and its inhabitants. Good enough to me...

The development of Central Saint Giles comprises a large 11 storey U-shaped office building to the east, and a smaller, separate 14 storey residential block to the west. All this is arranged around a central public space faced by bars, restaurants and entrance lobbies. It is a really dense group of buildings, providing office, hospitality and residential space on a constrained site in the London West End. Piano's design intention was to reduce the bulk of the buildings in three scales. First, by dividing the complex in two independent buildings (one for office and one for residential) surrounding an inner square. A secondary scale game was to break the large buildings in different heights and angles, so that one thinks the plot is really composed of around ten smaller, residential scale independent blocks. Finally, a wise use of colour and façade detailing further breaks the volumes and introduces a subtle degree of variety, through the use of thousands of individual tiles cladding the multiple separate facades of the buildings. By "fragmenting" the buildings in this way, their scale seems more domestic.

Piano has said about this game:
Fragmentation for me is one of the elements inspired by the place. It was a kind of obsession on this scheme - the spirit of fragmentation of the city, which has been growing in a kind of medieval, organic system.

Regarding the use of small pieces and the decision to introduce such bold colour into the building, Piano said:
If you want to use brilliant colour, then you have to break down the scale of the façade. The colour idea came from observing the sudden, surprising presence of brilliant colours in that part of the city. I don't think cities should be boring or repetitive. One of the reasons we have such beautiful cities is they are full of surprises.

The project team comprised Stanhope, Legal & General and Mitsubishi Estate as developers; Renzo Piano Building Workshop as architects, Fletcher Priest as executive architects and Arup as structural, services, fire and transport engineers. For what interests us in this blog, Emmer Pfenninger have been the façade consultants and Reef Associates the façade access consultants. The ground floor glazing parts have been built by Seele, whilst the ceramic and glass facades were built by Schneider Group. NBK supplied the terracotta elements.

Central Saint Giles is not a completely new construction, but a large brownfield redevelopment that has lead to the regeneration of a neglected area of central London. The land was formerly occupied by a dull Ministry of Defense building. The new mixed-use space includes 40,000m2 of offices and almost 10,000m2 of housing - 100 apartments – set around a new public square filled with cafes and restaurants. The transparent ground level of the building adds a feeling of permeability at street level, allowing passersby to see through and into the site, accessible by five pedestrian entrances leading into the public piazza.

Renzo Piano has specified ceramic or terracotta cladding for a number of his buildings, starting with two projects in Paris: the IRCAM building (a European institute for electro-acoustical music, finished in 1977) and the Rue de Meaux housing complex (1989-1991). Some other well known terracotta and curtain wall projects by Renzo are the Potsdamer Platz skyscraper in Berlin and the New York Times building in New York. Both use extruded ceramic pieces as sunshade elements, a.k.a baguettes. The approach in London is more complex, since terracotta has been selected here both for the front and the back elements of the facade.

Terracotta is really a modern version of brick, and we felt this material would work well with the surrounding buildings, says Maurits van der Staay, the project architect with RPBW. The surrounding brick buildings have a certain depth and we wanted to pick up on that by creating a cladding system with bespoke extrusions that would create different effects – we didn’t want a flat surface.

The architect had a team devoted to research on the facade texture - independent from the colour, already decided. During some months a group of young architects led by Lorenzo Piazza played with models at several scales until the decision was more or less clear. The game provided an intersection of horizontal shingle-like pieces with a grill of vertical and horizontal lines, that sometimes crossed in front of the glass units - two bars crossed at the residential windows, three bars at the commercial areas (as shown in the picture above). The vertical bars come in pairs, to provide a feeling of sculpting and shadow, but also because each bar is part of one facade unit behind, and so they can be perceived as a split mullion.

The ceramic elements on the building, fabricated by NBK in Germany, were mounted on facade units produced by Schneider Fassadenbau at their factory in Wroclaw, Poland. Schneider had some previous experience with combined terracotta and glass-aluminium unitized systems. They had done, also in London, the re-cladding of Collingwood House with Sturgis Associates architects, finished in 2008. For that project Schneider designed a mixed unit system of terracotta-aluminium curtain walling, with fixed brise-soleil set in extruded box frames. The step from Collingwood to Central Saint Giles was natural. To fabricate the whole façade as independent units would be quite convenient, avoiding the use of external scaffoldings after the installation of the glazed façade, thus reducing time and cost. The quality of the end product would also improve, as can be seen by the images of the units being mounted at the Schneider factory in Wroclaw (see images below, with yellow and grey units being fabricated).

NBK and Schneider worked together a set of detail connections between the terracotta profiles and the aluminium elements behind them. Terracotta profiles completely cover the unit outside face, so that the curtain wall looks like an opaque facade punched by windows (fix units at the offices, opening vents at the housing). The inside face of the panels is clad with white painted aluminium profiles and sheets, no ceramic being present at this side.

There are 18 different terracotta extrusion profiles in six different colours. The extrusions are pressed from a highly sophisticated mix of different types of clay, subsequently dried for several days, and then burned at high temperature for around 24 hours. After being cut to size, the ceramic material is brought on in liquid form, and the pieces are burnt a second time.

According to NBK, each extrusion has been drawn specially for the project, and further technically fine-tuned between RPBW, Schneider and NBK; each piece has been produced, adapted and tested several times during the design process. The detail below shows the degree of accuracy with which every element interfaces the others. Insulation below the window at section B and behind the jamb at section A is not shown, but it is located there. Terracotta acts as a rainscreen on the outside, with a pressure equalized intermediate space between the outer skin and the glass / aluminium face.

All in all there are 3,300 ceramic clad facade units on the buildings (2,300 on the office building and 1000 on the residential building). Each unit contains 32 ceramic elements on a total of more than 400 components. The total number of tiles on the buildings is around 121,000. The ceramic clad facades account for 60% of all upper floor facades.

Each façade element is approximately 370mm deep, and contains everything: the ceramic extrusions, the aluminium thermally broken frame profiles, the selective coating glass and the opaque infill with thermal insulation. The typical facade unit is 1.5m wide and varies in height from 3.9m for the offices to 3m for the residential. The final cost for the façade units is about £1,100 per m2 (around 1350 €/m2).

RPBW asked for three full-size mock-ups of the ceramic cladding unit to make sure they got it right, each one a refinement of the last. The most recent mock-up, located at the site, gave the architects the chance to see what the colours would look like in context and they were able to judge whether they had got the balance right between the depth and texture of the unusual ceramic extrusions. The complexity of the perimeter can be seen at the plan here below, with open corners and angled facades.

As the cladding was being installed on site a striking new landmark appeared, defined by dramatic facades of primary colours which at first glance seemed a bold contrast to this neglected corner of central London. Piano is clear about the selection:
The colour idea came from observing the sudden surprise given by brilliant colours in that part of the city. Cities should not be boring or repetitive. One of the reasons cities are so beautiful and a great idea, is that they are full of surprises, the idea of colour represents a joyful surprise.

The façade terracotta comes in six different colours: RAL 070 70 80, RAL 050 50 70, RAL 050 50 78, RAL 000 75 00, RAL 110 60 50 and RAL 7035 Light.

Central Saint Giles is not just about terracotta. There are three types of facades in the project:

the ceramic cladding units in six different colours;
the ground floor double-glazed facades that feature 300mm-deep triple-layered glass mullions evenly spaced apart and located behind the glass; and
the triple fully glazed facades located on the top floors of the office buildings and in the set-back facades between each coloured ceramic-clad facet.

There are some slight variations in the office and residential facades. Perhaps the most notable of these are the openable glazed louvres to the winter gardens in the southern corners, an area of special interest for Renzo. Another point of interest is the visitable top roof above part of the office block. In these two elements, Piano creates some intermediate or purely external spaces as venues for the building users. Here the office workers can smoke, sit, chat or just think while viewing the surroundings. The whole complex is not perceived as a massive volume from here.

The same happens at the ground floor level. Here the architect's intention has been to allow views through the buildings, from the street into the courtyard and from the inside piazza to the outside. The sheer volume seems to float above this glazed podium, without imposing itself upon the street walkers.

And finally, the facade surfaces. Imagine if these were clad in a flat curtain wall without the richness, texture and shadows of the terracotta fabric. The whole concept would have looked as a huge spacecraft abruptly landed on the West End. The facade is flat - only 370mm deep from inside to outside - in order to maximize the lettable space, but, miracles of architecture, it doesn't look like flat at all. Piano has found inspiration at the terracotta cladding of the best Chicago buildings from the end of the 19th century and their big glazed openings (the Chicago window, remember?).

The advantage is double: on one side, the scale is urban, tactile. On the other side, the amount of natural light inside the housing and office spaces is huge, almost as if the facade were a conventional floor-to-ceiling glass element. This seems to me as the perfect balance between a conflicting set of requirements: those of the developers, those of the neighbourhood, those of the city planning department and those of the future tenants.

The facade plays a significant role in this achievement, and it has not been an easy task at all. It's tempting to say at first glance that Piano was not at his best this time. After a review of the facts, I would say just the opposite: no one but a master would have been able to reconcile all these requirements and deliver a present to the city. A gift of colour that will keep the area alive for years to come. That's real value for money. That's what architecture is all about.

Mokuzai Kaikan: Japanese timber revisited in Tokyo

2010-11-01T08:26:00.390+01:00

Timber construction is an art, specially when deployed by the crafted Japanese carpenters of past centuries. Apparently, even if there are still artisans who keep some of its secrets today, the subtleties of Japanese timber joinery have disappeared from Nippon architecture. Kengo Kuma is the only name that comes to our mind if we think timber and contemporary Japanese architecture. But projects as interesting as One Omotesando in Tokyo (see the images below), with its main facade protected by thin vertical fins of larch wood, use timber more like a skin care rather than as a construction material. Timber here is the wrapping, not the real thing. The same technique was used by Kengo Kuma at the Nagasaki Art Museum, this time with louvres made of stone instead of timber - although it's difficult to find out from a distance!

Has timber joinery disappeared from contemporary Japanese architecture then? Well, not yet.

'The Art of Japanese Joinery' by Kiyosi Seike is the best introductory book into Nippon wood joinery as an artistic craft. The book starts with the history and philosophy of Japanese architecture as it relates to joinery, then follow many pages of great black and white pictures of wood joints. Only 48 types of joint are presented, selected from among the several hundred known and used today. Joints range from the simple scarf joint to the insanely complex ones. Some of them are truly puzzle-like in construction. The text continues with a chapter on the functions of Japanese joinery, then a chapter on Tsugite or splicing joints and finally Shiguchi or connecting joints, both of which have drawings showing the construction of the joints with hidden lines for further clarification (or obfuscation?)

Wikipedia will help us enter the world of splice joints or Tsugite. A splice joint, in Japan and elsewere, is a method of joining two members end to end in woodworking. The splice joint is used when the timber pieces being joined are shorter than the length required by the construction. Splice joints are stronger than (unreinforced) butt joints and have the potential to be stronger than a scarf joint. The most common form of splice joint is the half lap splice (see below left), used in building construction to join shorter lengths of timber into longer beams. Connection has to be achieved using glue, nails or screws. The beavel lap splice gains profit from geometry, with its dovetailed shape. Things start to get more complex with the tabled splice joint, where glue or nails aren't working in shear any longer.

A variation of the latter is the wedged tabled splice joint (see below right), where two interlocking wedges close the gap and secure the connection of the two timber pieces with each other. Here we don't need to nail or glue the joint and even better, we can disassemble the two pieces if and when needed. We got it: this is Tsugite, we have just entered the Japanese timber joint world.

Some may think this is nice stuff for DIY aficionados with time to spend on the weekends. Is there a way to apply the intricacies of joinery shown in Kiyosi Seike's book to real life construction? Where will we find the carpenters and the time for doing this - not mentioning the money to pay for it? There is a way, and it's called CNC woodworking machinery. State of the art woodshops today are employing computer numerically controlled pin routers to cut wood, and are using vacuum holding fixtures and autoclave-like devices for joining solid wood. They can even glue wood with glues that harden only in the presence of radio waves. A longish Youtube video - but worth seeing for a couple of minutes - shows one of these Japanese timber frame joinery machines at work.

So timber in Japan is an abundant material, there is a milennary joinery knowledge and there exists CNC machinery to cut and join timber for construction purposes. One would expect to see hundreds of buildings in Japan using timber as structural or as finishing material, both for outside and inside applications. That is not the case though, and this was the reason why Mokuzai Kaikan (the Tokyo Lumber Wholesalers Association) decided to promote timber as the material of choice at their new headquarters in Tokyo.

The Mokuzai Kaikan office project was commisioned to a big architectural firm in Japan, Nikken Sekkei. The numbers in this studio are impressive: founded in 1900, the firm was 29 strong by 1904 when they finished their first big project, the prefectural library in Osaka with a neo-classical style. Now they are almost 2,900 between architects and engineers, and their projects extend all along the Pacific rim. The Wholesalers Association project was directed by Tomohiko Yamanashi, principal at the architectural design department, in coordination with Takeyuki Katsuya. Yamanashi and Katsuya embraced the idea of promoting the use of timber as requested by their client, and wood became the leit motiv of the project.

This is the outline of the Mokuzai Kaikan project as it appears at Nikken Sekkei webpage:
This project involved the relocation of the offices of the Association of Wood Wholesalers in Tokyo. It serves as a showcase to demonstrate the possibilities of wood as an urban construction material. Engawa, or Japanese terraces, allow a natural breeze to enter while shutting out strong sunlight for a comfortable indoor environment. Lumber were integrated into the building's structure, and architectural exposed concrete was cast in cedar formwork. Since the building uses a large amount of wood, great attention was given to fire safety measures. The design focused on creating spatial continuity with the use of layering and natural light.

The building also revives and adapts another of Japan’s architectural traditions through the use of the Engawa (see night image to the left), a terrace space prevalent in traditional homes. In accordance with earthquake regulations, the 7,582m² seven-storey building employs reinforced concrete for its structural frame. Beyond this, timber was specified wherever possible. The architects paid close attention to detail, fitting the main concrete frame with the secondary timber elements. Concrete was cast in cedar formwork, maintaining the scale and grain of the timber (see below left).

In terms of the timber elements themselves, everything that can be seen is formed in 105 x 105 mm sections of Japanese cypress; a standard off-the-shelf product. These sections are used in composite panels to create the distinctive cubic Engawas, but they also form the remarkable longitudinal beams that span the full length of the 25m rooftop assembly hall. Here is where the art of Tsugite reappears, and in a way that mixes tradition with modern requirements.

Each cypress element is just 0.105m high x 4.0m long, and it had to be connected to those above, below and beside to conform a 1.6m high x 25m long beam. The connection system owes something to the traditional joinery - you can see timber wedges in vertical, combined with wooden oak plugs that connect every two pieces in horizontal. Tabled spliced joints can be seen both at the top and the side of every element. But there are also stainless steel rods - or should we say long bolts? - that keep all timber pieces working together as a 1.6m high beam. In order to avoid the concentrated tension around bolts to fracture the wood under extreme stress, cilindrical aluminium rings have been added around each passing bolt.

The exploded detail can be seen here below, extracted from an article about the Mokuzai Kaikan office appeared on The Architectural Review. The following images, the assembly room plan at the upper storey, the vertical section and the Engawa 3D drawing have also been taken from the same article.

The Mokuzai Kaikan office was built between Nov 2007 and June 2009. The project received a Special Jury Award at the 3rd annual MIPIM Asia Awards 2009 held in Hong Kong. I invite you to see some stunning images of the interior here (go to the bottom of the page)

How will the lumber perform on the outside say 10 years from now? This remains to be seen. I have not found any information about the surface treatment these cypress logs have undergone - if someone out there knows more, please shout. One final critique has to do with the side facade, visible at the images from the link above. That facade doesn't seem to be the best part of the building. But all in all, Mokuzai Kaikan is a great example of architecture well delivered at all levels, from the concept phase to the 1:1 details, from programme to materials selection. The front facade is an example of intermediate, filtering space, one that moves forward from the typical flat, barrier-like glazed facades we are used to these days.

There is another project I find vaguely similar to this one, located in a very different place place and context: Louis Kahn's Salk Institute at La Jolla in California (1959-1966). Sorry, but I can't find a better way to finish this post than by paying a little homage to the old master.

The Ledge at the Sears Tower in Chicago: glass is the limit

2010-10-30T17:54:00.012+02:00

There can't be more stories written about the design, engineering and construction of such a small part of a building as for The Ledge, the latest attraction at the tallest observation point in Chicago. The Ledge is really small in number: just four glass boxes, all the same. And it's small in size too: each box is 1.3 x 3.2m in plan, and close to 3.6m high. But there's one detail that makes all the difference: these four fully glazed boxes are cantilevered from the 103rd floor of the Sears Tower, at 413m above the ground. Glass Google pages and technical papers at recent facade conferences are filled with stories about it.

Why so much fuss about glass boxes? Well, the image says it all.

The Sears tower (since 2009 sadly renamed as Willis tower) remains the tallest building in the Western hemisphere. Completed in 1973, its 442m (without counting the spires) are still today an impressive height for a building. The Sears tower observation deck, called the Skydeck, is located on the 103rd floor of the tower, and its view 412 m above ground is one of the tourist attractions in Chicago. Visitors, up to now, could experience how the building sways on a windy day. Now they can also feel a different sensation: that of sheer vertigo.

In January 2009 the tower owners began a major renovation of the Skydeck including the installation of four glass balconies, extending approximately 1,2m over the west facade from the 103rd floor. The all-glass boxes allow visitors to look through the floor to the street 412m below. The Ledge opened to the public on July 2009.

The Skydeck renovation project was awarded to Skidmore Owens and Merrill (SOM), the architects who designed the tower. The picture above shows a realistic image of their intention: glass all around, no steel structure at all if possible. “The Sears Tower set architectural and engineering standards when it was first built and now we are able to carefully craft new elements that expand the capabilities of the original design while retaining its integrity,” said Ross Wimer, design partner with SOM and one of the fathers of The Ledge idea. A 360º view of one of the glass boxes (this is not a render) is the nearest you can be to the real sensation of stepping in (or out?) there.

Architects must be praised for the idea, but engineers - glass specialists - were needed for its detailed design and realization. The building owners contracted Halcrow Yolles in Toronto as engineers for the observation boxes, and gave them the responsibility of fully design and detail the glass and steel components. Halcrow's senior principal and structural glass engineer was at the time John Kooymans, one of the few who can say 'The Ledge is my baby'. Around the end of 2009 John moved from Halcrow to another Canadian engineering team, MTE Consultants in Ontario (the name means More Than Engineering). If you visit Halcrow and MTE webpages you will find how both companies claim having authored the engineering design of The Ledge - and both are right!

There are two articles describing the design of the glass boxes both written by John Kooymans, one as part of Halcrow Yolles and the other one written this year as member of MTE. According to the first paper, publised in Glass Performance Days 2009, the challenges to solve were many:

All glass elements had to be brought up to site using the internal elevators, which limited the size of the box elements.
The observation boxes had to be moveable. This was required to allow the facade maintenance equipment to operate along the facade without interruptions. But, even more difficult, it was decided that the glass boxes were to be retracted an additional 1200mm into the floor space, so that glass maintenance and cleaning could be done from inside the building.
There was tenant at the floor below the Skydeck, so all the glass box loads had to be hanged and framed from the ceiling above, in order to avoid interferences.
Design loads and movements to be imposed onto the glass structure would be very high from the calculation stage. The frame and glass box had to be stiff enough to allow the movement of the box without creating large deformations or stresses at the glass connections.
The details around the glass box had to include weather seals in both the extended and retracted position, allowing for the movement of the tower, and for the seal to be temporarily broken while the assembly moved from one position to the next.
The architectural intention was to obtain maximum transparency, including the floor and the roof, minimizing the visible structural steel elements.
Structural redundancy (safety) and protection of the glass were requested. But, to speed the use of the balconies, visitors would not be forced to protect their shoes when entering. Safety issues excluded the option of double glass, and laminated glass was the solution.
Outer temperatures should not create a risk of condensation on the glass, or worse allow the formation of ice shards outside the boxes, falling onto the walkway behind. So, the design had to introduce some kind of heating system as well.

The second paper by John Kooymans is the one that originated this post: I read it at the proceedings of Engineering Transparency, a conference held in Glasstec Düsseldorf last 29 and 30 September. Carlos Prada and María Meizoso, two colleagues from Arup Facades Madrid, attended the conferences and brought the news back to us. You can have access to the paper here, through the MTE webpage.

Each box face can withstand design wind pressures of 4.6 kPa, and the roof and floor wind pressures of 6.0 kPa. At the floor there is an additional live load of 4.8 kPa due to its intended occupancy. As Kooymans puts it, it can essentially hold more people than it can fit.

The corners and intermediate joints where the different wall panels come into contact with each other are simply stitched together with stainless steel angles and through bolts. The floor is stitched to the glass walls creating small local opaque connections that allow for the transfer of external loads into the hanging glass panels and subsequently, into the steel cantilevered frame.

From John's Glasstec paper:
The glass had to be designed with enough redundancy to ensure that any accidental breakage would not result in a total collapse of the system. For this reason, three layers of glass were selected for all the elements. The structure was designed so that only two layers of glass were required to resist the design loads, and only one layer of glass would be able to support the self weight of the structure. In addition to this design decision, the glass floor was constructed using an ionoplastic interlayer (SentryGlas Plus) captured by the through bolts in the floor which would ensure the stiffness of the tempered floor panel would remain intact in the remote possibility that all three structural glass lites failed.

In the end, the glass box elements are all created with three layers of 12 mm tempered low iron, heat-soaked glass. The requirement of heat-soaking helped eliminate the potential for spontaneous breakage due to nickel-sulphide inclusions.

If the engineers of The Ledge were Canadians, the facade contractors are pure Chicagoans, and making part of the city building history. MTH Industries, located in Hillside, Illinois, started building glass facades in Chicago back in 1886. Upon first hearing about the project, Ludek Cerny, vice-president of glazing at MTH Industries, thought it was pretty unusual. Because of that, MTH wound up taking on a design-assist role.

Load tests done in-house by the contractor (see images above) involved loading a glass lite that was half the size of the actual floor of the bays to 2½ times the required code load for a 24-hour duration. “The test was later repeated with fracturing one of the lites with the actual design load,” Cerny says. That wasn’t enough for this team: “Out of curiosity,” Cerny says, “we actually broke more lites and realized that you could still stand on the glass floor with all of the lites broken.” Miracles of ionoplastic interlayers.

In addition to avoid damage from breakage, the design includes ways of protecting the bays from daily wear as well. There is an anti-graffiti film on the inside of the vertical glass units. The laminated floor has a 6mm sacrificial layer of fully tempered, heat-soaked glass on top that can be removed or replaced if it gets scratched, cracked or damaged. The stainless steel fasteners that support the glass panes to each other are bespoke and have been custom-machined by MTH.

The motorized system that projects and retracts the boxes from the building utilizes steel LinearBeam mechanical linear actuator systems. The systems operate with a rigid chain technology. A rigid chain is a mechanical actuator that is flexible in one direction and forms a steel beam in the other direction. The contractor worked with the supplier to design the locking pins and the control systems that secure the bays.

Because of the movement, the perimeters of the bays are lined with inflatable seals. When the bay is in the viewing (outside) or in the maintenance (flush) position, the seals inflate to create a secure air and water lock for the building.

Vertical movement - that is, transporting the box material up to the 103rd floor - proved to be one of the bigger challenges for the contractor. The installers moved the glass units and the 5.5m suspension beams up on the top of elevator cars. To ease the material handling, MTH ended up creating custom tools to help hoist and carry. “It was all a conglomeration of things that already existed modified to work under these conditions in the space allowed,” Cerny adds.

The laminated glass units forming the walls and the roof have three tempered 12mm lites of PPG's Starphire low-iron glass. The walls and roof are laminated with clear PVB, while the floors are laminated with 1,52mm DuPont’s SentryGlas Plus interlayers. The glass fabricator was Prelco of Montreal. Prelco delivered its last panel in April 2009, six months after the company began fabrication and two months before the end of the installation on site.

This article from The New York Times has a very interesting short video abour the building of the Ledge. Scroll down and you'll find it on the right. Not to be missed!

The final image is my personal homage to the vision of all the people involved in getting these glass boxes real: from the owner to the architect, engineer, contractor and every supplier. Compare this image with the first render, drawn by the architects in 2008. One year later, the built thing is astonishingly similar to the design intention. In fact, it is even better: by selecting low iron glass, the green aspect of the standard glass used in the first image has disappeared.

Could such a small job have been done better?

Arup and facade engineering

2010-10-16T00:17:00.006+02:00

This is my post nº 22. This blog has had more than 1,100 visits up to now, in less than two months after I started writing it. Not bad!

It's time to get a bit more personal, and tell you, dear reader, what I do for a living. I am a facade engineer, or a facade specialist, or a facade consultant - it's all the same more or less. I work in Arup, a big engineering firm based in London but with offices in all continents. My desk is in Madrid, but my projects are - and have been - in many places around the world. That's of course a fantastic experience.

There are almost 300 facade engineers in Arup if we count all offices. The discipline started in London around 1985, and I think we are now the biggest facade consultant in the world. Our offices with facade dedicated teams are located in the UK, Ireland, Germany, Italy, Netherlands, Spain, Denmark, Dubai, South Africa, Australia, Singapore, China, Japan and the US. The facades team in Madrid started in 2004, and we are 10 people between architects and engineers. We have taken part in projects as interesting as the image below: the Bridge Pavillion in Zaragoza with Zaha Hadid. We have been lucky enough to work with well-known architects as Rogers, Foster, Zaha, Piano, Chipperfield, Arup Associates, or Spanish firms as Rafael de La-Hoz, Lamela, Nieto Sobejano, DL+A, MBM, Ferrater, Vidal or Cruz y Ortiz. We also work for developers, usually helping architects to develop the trickiest parts of facade designs, acting as site specialists during construction, conducting failure investigations or leading the facade refurbishment of existing buildings. Sometimes we also do systems research and development for facade contractors.

I love being a facade engineer because of the combination of skills it requires. As old Vitruvius used to say, it has a bit of firmitas (resistance, durability), a bit of utilitas (performance, confort, modularity) and a bit of venustas (proportion, colour, texture, beauty). Wasn't it the definition of architecture? Precisely. The question is that these days, because of the complexity of the building profession, one cannot be an architect and understand everything of a building in a holistic way. There are two options: either you remain a generalist and rely on teamwork for the project to achieve a global view, or you become a specialist in one specific area of knowledge, as facades. In this case you can still have a complete understanding of your branch, combined with a minimum amount of details of the surrounding areas. Engineers have always tended to subdivide their bodies of knowledge; architects have up to now resisted such a temptation. As an architect, I think we were wrong. Someone can argue that my work is not that of an architect, but of a building engineer. I take the point: being a building engineer is a way of being an architect, just as being a civil or an electrical engineer are ways of being an engineer.

Facades are a great topic because they involve almost everything an architect did in the good old days (except plan distributions obviously), so you still feel you are in command, and your area of expertise is still very wide. In fact, I now consider myself a facade generalist rather than a facade specialist - it's becoming impossible to be a real specialist in such a wide discipline as ours!

British people love belonging to clubs. Today's equivalent to the classic clubs are professional fellowships, where Brits feel like at home with their peers. Times have changed for good, and these professional societies do welcome women and foreigners as members. Our club is of course the Society of Façade Engineering. And what is the definition of façade engineering to this honourable Society? There it goes:

“Façade engineering is the art of resolving aesthetic, environmental and structural issues to achieve the enclosure of habitable space.”

You see? There's Vitruvius again, and I swear I wasn't aware of this definition until now. Sounds good to me (and rather Brit as well). The Chairman of the Society is my friend and Arup colleague Mikkel Kragh. Mikkel is Danish as Ove Arup, our founding father, which makes him a sort of square Arupian. He is now living in Milan and leading a growing Arup Facade team there, apart from chairing the Society and doing several research and academic activities. Mikkel has written an article on the role and challenges of façade engineering, "Façade engineering and the design teams of the future". He points out that our trade is not only a business of architects and engineers, but also one for facade contractors:

The façade engineering discipline is embedded in various aspects of the work of Architects, Engineers, and Specialist Trade Contractors and we will see an increasing need for seamless collaboration and delivery of integrated systems as opposed to elements and components. We have witnessed a recent trend of design teams going from multidisciplinary to interdisciplinary, with disciplines interacting and working closer together.

This is a really serious point: integrated systems as opposed to elements and components. The integration of different functions, not just the co-existence of independent systems as part of one skin, seems to be the strategy for the future of façade technology and design. I believe this is the way too. There is more on this matter in a paper from Tillman Klein, who leads the Façade research group at the Faculty of Architecture in Delft, "Evolution or revolution of systems in façade technology". This article is part of the book "The future envelope 1 - a multidisciplinary approach", edited by Ulrich Knaach and Tillman Klein.

But design and construction are just parts of the whole story of facades. New materials, the quest for optimum energy performance or the support for energy generation systems are requirements that meet with predominantly conventional crafts. Our role as façade engineers in every project is to lead a conversation between these diversely interested disciplines into a converging interdisciplinary team, a team that will not put one interest too much above the others. It sounds like a complex task, but the final result should be simple: as the good movies or buildings we remember long after having seen them.

Should we façade engineers expect to receive prices or accolades? Nope. By the time for the party and the distribution of medals after the opening of a building we are already hands on with the next project, where the action - and the learning - is. Our medal is to have taken an active role in designing, fabricating and building facades that stand the passing of time, perform well and mean something to people. Our medal is to have avoided failure to happen more than once. Our medal is to contribute to the delivery of better buildings that become sounding pieces of better cities.

Isn't it a great career?

Cook vs Gehry on designing the best NYC skyscraper

2010-10-10T18:39:00.445+02:00

Last August Paul Goldberger, The New Yorker’s architecture critic, spoke with Richard Cook, founder and partner in Cook+Fox Architects and the designer of the new Bank of America Tower. The Manhattan skyscraper, a.k.a. One Bryant Park, was completed earlier this year and is the largest commercial building to receive a LEED Platinum certification, the highest standard set by the U.S. Green Building Council. Cook and Goldberger indulge in a polite conversation about sustainable design, LEED certification and the meaning of green consciousness for architects nowadays.The critic does not perform as a critic; he seems convinced by the elegant, soft-spoken and well-educated leader of Cook+Fox Architects. My impression - I must admit it - was not so positive. There is something about this glazed tower that seems rather opposite to the concept of a sustainable building, and that's the huge amount of vision glass that covers the facade top to bottom. A similar percentage of vision glass than at the Lever House or the Seagram Building, to name just two icons of New York curtain walls in the 20th century.

The message in the video was well packaged and sent though. A quick review to the Bank of America Web page brings some more info:

Bank of America Tower at One Bryant Park is the heart of our New York operations - and a striking example of our environmental commitment. The 55-story tower, having obtained the U.S. Green Building Council's LEED® (Leadership in Energy and Environmental Design)- CS Platinum certification, is one of the world's most environmentally responsible high-rise office buildings.

Unlike most large buildings, the tower will generate a significant portion of its power on site through a 5.1 megawatt cogeneration system. It also will save about half the energy used by most buildings its size; will filter out about 95 percent of the particules in the air drawn into the building; will use less expensive night-time power to produce ice used to cool the building; and will conserve millions of gallons of water every year through methods such as green roofs and waterless urinals.

Even the Huffington Post, a reliable NYC politics and socialite Web page (not precisely conservative) seems to have joined the praise.

There is another tower in Manhattan, still under construction, which is not known by its sustainable credentials but by its designer, Frank Gehry. The Beekman tower, located just south of City Hall, has recently received a positive review at the art & design pages of The New York Times. The 76-story tower is recognizable by its crinkled stainless steel skin, bringing a new look to an imposing cluster of landmarks from a hundred years ago commanded up to now by the Woolworth Building.

The design of the Beekman tower has evolved through an unusual public-private partnership. In an agreement with New York education officials, the tower’s developer, Forest City Ratner, agreed to incorporate a public elementary school into the project. Forest City was responsible for the construction of the school; the Department of Education then bought the building from the developer. The Beekman tower is thus a curious fusion of public and private zones. Clad in simple red brick, the school will occupy the first five floors of the building. Atop this base will be the elaborate stainless-steel form of the residential tower.

As IBM ads tell, it's time to ask smarter questions. From the available literature, Cook+Fox are the nice, responsible guys whilst old Gehry, in his Southern Californian mood, has come to Manhattan just for the money. Is it as simple as that? Not really.

Let's have a look at the vertical section of One Bryant Park:

Two-thirds of the facade surface - floor to ceiling - are covered with vision glass, only one-third - the edge of slab - is opaque glass with a back-panel insulation. The tower has been clad with Viracon insulated glass with a low-e coating and a silk-screen pattern made of fritted dots on the #2 surface. To allow for higher transparency, the glass is low iron (extra clear). At eye level (sit or standing) the glass has no pattern, providing great views of the New York skyline. The silk-screen pattern extends graduately below eye level to the floor and above eye level to the ceiling to reduce radiant heat gains. These are the best data I could find from the glass supplier, not from the project, so take it as a guess (the glass coating is a project specific combination of VE 15-2M and VRE 15 -59 from Viracon): U-value 1.6 W/m2ºK or 0.30 BTU/hft2ºF, solar heat gaining coefficient between 0.36 and 0.39, visible trasmittance between 55% and 73%.

“Bringing in more daylight deep into the building reduces electricity costs. But it also increases the efficiency of the people that work in the builiding – and that's the greatest cost savings,” says a spokesperson from the developer, adding that financial firms' personnel costs are several factors higher than their energy needs. “If you're 10% more efficient on energy, it's not the same dollar amount as a 2-3% in personnel savings"

This sounds familiar to most of us involved with glass and energy efficient buildings. The architects seem to have convinced the developer that lots of light are good for tenants, and energy losses (or gains) through the glass are secondary. The solar passive behaviour of a glazed tower must be relative, since it doesn't impede the building to achieve a LEED platinum certification. It is true if you use LEED as the only metering system, but it is not true if you really try to minimize the total heat exchange through your facade. Lets have a look now at the curtain wall unit system detail (vertical section through the top-bottom interlocking transom):

The glazing contractor for the project, by the way, is Permasteelisa USA. Do you miss anything in this section? I do: a good old thermal break in the transom profiles. OK, so we have here a non-thermally broken unit system with a combination of 2/3 vision glass (U-value of 1.6 W/m2K centre pane) and 1/3 opaque glass (100mm of mineral wool plus insulated glass, that should be around 0.6 W/m2K centre pane).

We Europeans may be a bit pesimistic when doing U-value calculations, but the combination of those three elements (profiles, vision and spandrel glass), according to our standards, delivers an overall U-value between 1.9 to 2.3 W/m2K. Let's add to it the radiant heat gains: all orientations have the same glass, there are no external shading systems, and 2/3 of the glass is vision, with an average solar heat gain coefficient of around 0.35 (deducting the profiles but adding the radiant heat that enters through the non-thermally broken aluminium). What does this mean? Two things: important heat losses in winter and very important heat gains in summer, both along the whole working day. As a result, a) services must have been designed to cover peak loads, at an important extracost, and b) energy consumption along the year will be clearly higher than if designed otherwise. The energy performance of this curtain wall is much better than the Seagram or the Lever House from the 50s, of course, but it's nothing extraordinary nor any example of energy efficiency in buildings. I will skip the glare issue here, but I bet not all Bank of America clerks are happy about their transparent facade when they try to read their computer screen at the office.

But then, who is wrong? Wasn't it an example of environmental commitment? According to LEED, yes it is. According to some of us, there is much room for improvement - both in the design of this facade and in the way LEED points are measured and obtained. You can find more on the matter at this interesting webpage, written by Steve Mouzon: One Bryant Park and the LEED problem. I completely agree with his point of view about LEED: the US Green Building Council has made a lot for achieving better buildings and deserves our praise, but it's time for a change in the way LEED points are given. One sole change to begin with, please: all Gold and Platinum pre-qualified buildings should measure their energy output once they are built and occupied, and compare real life results against simulations, if they want to receive the final medal.

Time to come back to our old Frank Gehry and his slender residential Beekman tower. The developer here has not opted for a LEED certification (at least that I know). Compared to One Bryant Park, though, the project is quite reasonable in terms of facade energy performance.

The stainless-steel folds that now drape all but the top few floors of the Beekman Tower have already created a new landmark on Lower Manhattan. “I designed this building for New York,” says Gehry. “I’m a deeply rooted contextualist regardless of what anybody says. I stair-stepped the building like a New York skyscraper. It fits in without pandering to, or copying, its neighbors”.

To produce the tower’s wavy skin in a cost-efficient process, the facade concept is based on a flat, unitized curtain wall with a back-ventilated rain-screen cladding attached to its front. Permasteelisa (once again) was selected as the facade contractor. You will read lots of papers about the computer design process, Rhino, Catia, etc. This is not our stuff right now, we are just onto sustainable performance today.

Let's have a look at a the facade plan section. The folds of the facade become something as bay windows for the apartments, providing top and lateral shadows along the day. The residents will feel they are living within thick walls, at least that's the impression one gets from the plan section. This is a good feeling, don't you think?

The amount of opaque surfaces in this facade is much bigger than at One Bryant Park. All columns, partitions and parapets are clad with 16-gauge stainless steel face sheets, hiding a thick mineral wool insulation behind. The curtain wall elements are thermally broken. I haven't found any data about the glass yet, but I bet it's a low-e double glass unit without any additional coating.

The external wall looks really well from a nearby position. OK, stainless steel is not cheap, and these flumsy shapes are not easy to do. Even though, if we conducted a life cycle analysis of this facade, I wouldn't be surprised to find out that the low energy transmission - both during winter and summer - plus a low maintenance operation cost can offset the extra construction cost in a few years, making this facade more sustainable in the long term than the Bank of America's one. LEED permitting, of course.

Who knows? Maybe Gehry is more aligned with the real spirit of New York facades than Cook+Fox: a spirit that favours tall, vertical windows, stepped-back volumes and decorated external walls. There's nothing wrong about it, after all...

Industrialized building speech

2010-10-04T22:58:00.120+02:00

Believe it or not, Nikita Khrushchev, one year before becoming the next USSR president after Stalin, delivered a long speech about prefabricated housing and its challenges. It was back in 1954.

The speech title was: 'On the extensive introduction of industrial methods, improving the quality and reducing the cost of construction'. The speech was given at the National Conference of Builders, Architects, and Workers in the Construction Materials on December 7, 1954.

What is this post about? A Google search took me by pure chance to the highly recommendable Dutch quarterly Volume, dedicated to architecture and design. The speech text is a free access article appearing on a recent issue (2009-3), named 'The block' and dedicated to mass housing. From the editorial:

Housing the billions: never before were those involved in architecture and construction confronted with such a challenge. World-wide there will be housing needed for some three billion people in the coming forty years. In the Netherlands, after the post-War ‘reconstruction period’ during which dealing with ‘the big number’ was the central issue, attention shifted entirely to the individualization of design.

Here and in much of Europe we have indeed bid farewell to blueprints, repetition and uniformity, but is that farewell as definitive as we think? Is this extreme individualization sustainable? Is there not something to be learned from mass construction and the industrial production of housing such as, for example, from that which houses and provides an urban environment for 70% of Russia’s population?

Another accessible article is 'Standards, classes, formats', by Bart Goldhoorn, one of the main contributors to the Volume issue. This is a glimpse to its content:

In architecture, to use the word “standard” seems to be a taboo. ...The experiences of the 1960s and 1970s in mass-produced architecture have apparently been so traumatic, that this has led to the creation of a dogma in architecture and urbanism that translates as diversity = good, uniformity = bad.

...The dogma of architectural individuality excludes from discussion a field of knowledge and experience which is essential to the development of any contemporary form of manufacturing. ...In processes of design, production and marketing the use of standards actually enables innovation and diversification. True, the nature of these standards is very different from the way they manifested themselves in the mass housing project of the 1960s. ...It is time to break the taboo and consider the application of this experience in the field of architectural design – not as an aim in itself, but as a key to make good design available to more people.

I also think this is a very important problem, one that should concern us as architects, and one we will have to deal with in the coming years. Now, what can we learn about the Russian race to mass housing construction of the 50s, 60s and 70s? If the Volume issue is right, we should take lessons from the mistakes of those days, and try not to repeat them.

Under this light, Khrushchev's speech from 1954, delivered right at the start of the Soviet mass pre-fab housing process, is a pivotal document because it contains the key to what was going to fail later. My first impression at reading the speech has been of surprise: I could have never imagined a high rank politician of any country (not even Castro in Cuba) dealing with a technical issue with such level of detail, knowledge and, yes, passion. Later in the text Khrushchev declares himself a traded plumber in his youth, and then you start understanding what was going on there.

A visit to Wikipedia brings more interesting data: yes, young Nikita was welding pipes in Ukranian mines back in 1914. As a skilled metal worker he was exempt from conscription in the Great War. Between 1934-35 we find Khrushchev as superintendent of construction of the Moscow Metro. Faced with an already-announced opening date of November 7, 1934, Khrushchev took considerable risks in the construction and spent much of his time down in the tunnels. When the inevitable accidents did occur, they were depicted as heroic sacrifices in a great cause. The Metro did not open until May 1, 1935, but Khrushchev received the Order of Lenin for his role in its construction.

In 1950, as head of the Communist Party in the Moscow region, Khrushchev began a large-scale housing programme for Moscow. A large part of the housing was in the form of five- or six-story apartment buildings, which later became ubiquitous throughout the Soviet Union. Khrushchev had favoured the use of prefab reinforced concrete panels, greatly speeding up construction. These structures were completed at triple the construction rate of Moscow housing from 1946–50, lacked elevators and in some cases balconies. The blocks were nicknamed Khrushyovkas by the public. Almost 60 million residents of the former Soviet republics still live in these buildings today!

But in 1954, at the time of the speech, the construction of Khrushyovkas was just starting. The decision of using pre-fab instead of monolithic concrete construction had just been taken, not without pain for those who favoured the latter. Quoting from the speech:

Our builders know that until recently there was debate over which of two paths we should take in construction – use of prefabricated structures or monolithic concrete. We shall not name names or reproach those workers who tried to direct our construction industry towards use of monolithic concrete. I believe these comrades now realise themselves that the position they adopted was wrong. Now, though, it’s clear to everyone, it seems, that we must proceed along the more progressive path – the path of using prefabricated reinforced-concrete structures and parts. (Applause.)

Further in the text Khrushchev goes against architects. He complains that standardized construction can't succeed if architects keep insisting on non-standard design. Design offices were of course a collective activity by then in the USSR, but interestingly architects had somehow managed until then (after Stalin's death, that is!) to remain loyal to their design individuality. The boss is not happy with this:

They [architects] all agree that use of standard designs will significantly simplify and improve the quality of construction, but in practice many architects and engineers too aspire to create only their own one-off designs.
Why does this happen? One of the reasons, evidently, is that there are flaws in the way we train our architects. Led on by the example of the great masters, many young architects hardly wait to cross the threshold of their architecture institutes before wanting to design nothing but unique buildings and hurrying to erect a monument to themselves. If Pushkin created for himself a monument ‘not made by human hand’, many architects feel they simply must create a ‘handmade’ monument to themselves in the form of a building constructed in accordance with a unique design. (Laughter, applause.)

Now Khrushchev goes more personal. In a purely Stalinesque style, he attacks a such comrade Mordvinov, president of the Academy of Architecture and also present at the speech (I imagine not with a very lively face at this part):

If an architect wants to be in step with life, he must know and be able to employ not only architectural forms, ornaments, and various decorative elements, but also new progressive materials, reinforced-concrete structures and parts, and, above all, must be an expert in cost-saving in construction. And this is what comrade Mordvinov and many of his colleagues have been criticised for at the conference – for forgetting about the main thing, i.e. the cost of a square metre of floor area, when designing a building and for, in their fascination with unnecessary embellishment of facades, allowing a great number of superfluities.

It's difficult not to agree to a certain extent with the basis of this critique, if we realise that the issue under discussion was building houses by the thousands for a population that were living almost in barracks after the war end. More ammo was thrown to the audience:

Certain architects have a passion for adding spires to the tops of buildings, which gives this architecture an ecclesiastical appearance. Do you like the silhouette of churches? I don’t want to argue about tastes, but for residential buildings such an appearance is unnecessary. It’s wrong to use architectural decoration to turn a modern residential building into something resembling a church or museum. This produces no extra convenience for residents and merely makes exploitation of the building more expensive and puts up its cost. And yet there are architects who fail to take this into account.

Khrushchev, once convinced he had made a clear point here - several other examples are served in the conference, with numbers, unit cost comparisons and quotations - changes subject to another hot topic: improving quality of construction. It was already evident to this generation that quality would be the main issue of the housing programme in the future, one which would probably never be solved but against which a dialectic fight had to be launched from day one. Here goes our Quixote:

Recently comrades Bulganin, Mikoyan and myself had to visit many cities in the Far East, Siberia, and the Urals. We were looked after well. Which is understandable – given that we’re demanding guests and that we have the power to criticise – and in fact do even more than just criticise. So naturally they tried to ensure the best conditions for us. (Laughter, applause.) In the city of Sverdlovsk we lived in a hotel. It has to be supposed that we were given by no means the worst rooms. (Laughter.) And in this hotel we saw that the bathroom and toilet blocks were very badly built and that the quality of decorative work was poor. We asked for the hotel director and the city leaders and said to them: ‘Look how poor this work is!’
The quality of the tiling was poor and it had been carelessly laid. The pipes in the toilets and bathrooms were covered in rust and had been hurriedly painted with some sort of grey paint before our arrival, with more paint being splashed onto the walls at the same time. The way that these pipes had been joined together was very bad and I, as an ex-plumber, was very indignant: even in pre-Revolutionary times pipe joints down the mine were done better and more cleanly than in this hotel in Sverdlovsk.

The actual Khrushyovkas designed and built after 1954, up to and during the Brezhnev era, were not precisely a model of high quality, but they were an example of pure standardization. The leader was to be followed in this point, if not in quality. In 1954-1961, engineer Vitaly Lagutenko, chief planner of Moscow, designed and tested the mass-scale, industrialized construction process, relying on concrete panel plants and a fast-track assembly schedule. In 1961, Lagutenko’s institute released the K-7 design of a prefab 5-storey that symbolised the Khrushchyovka. 64,000 units of this type were built only in Moscow from 1961 to 1968, but it was just a beginning. In Moscow, space limitations forced a switch to 9 or 12-story buildings (these with lifts) at the end of the 60s. The last 5-story Khrushyovka was completed there in 1971. The rest of USSR continued building Khrushyovkas until the fall of communism; millions of such units are now still inhabited and well past their design lifetime.

The facade units, serving both as structural and cladding panels, were made at concrete plants and trucked to the site just-in-time. Lifts were considered too costly and time consuming, and according to Soviet standards, five stories was the maximum height of a building without an elevator. Thus, almost all Khrushyovkas have five stories.

Khrushchyovkas featured combined bathrooms. Lagutenko refined the space-saving idea, replacing regular-sized bathtubs with 120 centimeter long "sitting baths". Some theorists even considered combining toilet bowl functions with the shower's sink, but the idea was discarded. Kitchens were also small, usually 6 square meters.

Typical apartments of the K-7 series have a total area of 30 m2 (1-room), 44 m2 (2-room) and 60 m2 (3-room). Not big really, but that was not their greatest defect. Construction was really bad: issues of water penetration, excessive air permeability and low acoustic insulation between apartments (due to thin internal non structural partitions) have been constant complaints among its users. The main problem though was to be the incredibly low thermal insulation, both at the concrete walls and at the metal windows. Users had to install double windows, and close balconies at those models who had that privilege. Harsh living conditions in the Russian long winters and the anonimity of the blocks, all five stories high and impossible to differenciate even between cities, gave Khrushchyovkas a bad reputation almost since day one.

This long post should be finished in a positive way. First, citing some lessons learnt for future mass housing projects. We should care less for absolute equal repetition of the model: that is not standardization, that is Social realism in its whole crudeness. Camper shoes, Ikea furniture and Zara garments tell a different story: they are recognizable products, mass fabricated, affordable, but we want to have them. Houses could be made as well designed, mass consuming products and we would love them as well. We should care more about performance when designing and building affordable houses. In fact, because of their high compacity and relatively low % of glazed openings, housing blocks are easy to insulate and to protect from wind, air and water infiltrations. We now know how to do it, in an interesting way and within budget.

There is more good news coming for the old Khrushchyovkas. They can be renovated and brought back to an appealing consumer state. An article at The St. Petersburg Times in 2001 brings us the story: the lowly krushchyovka may be given a new lease of life, at least if the Danish Foundation for the Construction of Attic Apartments in Russia has its way. The foundation presented its pilot project for the reconstruction of some of St. Petersburg's most unappealing housing. The Danish foundation, aided by six Scandinavian commercial companies, has carried out a pilot reconstruction project at a block in St. Petersburg. The project, which took only nine months to complete, added a mansard for nine apartments, insulated the facades from the outside to improve heat retention, changed windows, closed balconies and renovated the building's heat plant.

Now the gleaming six-story building with glassed-in balconies and fresh white paint is the envy of the neighborhood, surrounded by its decaying former twins. This project is one way of prolonging the life of these buildings for another 50 years, according to Lev Khikhlukha, who directed the program for the Russian branch of the Danish company Velux. Not bad, don't you think? And the old ex-plumber would have probably been happy with the quality - at last.

An interesting book on pre-fab housing during the 20th century (not just Soviet blocks, obviously) is 'Home delivery: fabricating the modern dwelling' written by Barry Bergdoll and Peter Christensen and edited by the NY Museum of Modern Art. The Google book link is quite complete.

Hot spots and death rays - a burning issue

2010-10-01T07:27:00.021+02:00

This is the news from The Telegraph.co.uk, yesterday morning:

Guests burned by 'death ray' from Las Vegas hotel
Holidaymakers at the Vdara hotel reported that their hair had been singed and that plastic bags had melted in the heat of the hotel. The hotel's owners said that the tall, concave tower collected and intensified sunshine to create what staff call a "death ray" focused on the swimming pool area.

Bill Pintas, a lawyer from Chicago staying at the hotel, said that he suffered from the heat soon after noon one day. "I'm sitting there in the chair and all of the sudden my hair and the top of my head are burning," Mr Pintas told ABC News. "I'm rubbing my head and it felt like a chemical burn. I couldn't imagine what it could be. I used to live in Miami and I've sat in the sun in Las Vegas 100 times," he said. "I know what a hot sun feels like and this was not it."

Mr Pintas also showed how the black lettering on his white plastic carrier bag had been burned through by the sun. Plastic bags are typically made of polyethylene, which melts at about 120 C.

Gordon Absher, a spokesman for MGM Mirage, the hotel's parent company, said they were aware of the problem. "Because of the curved, concave shape of that hotel, they sometimes get isolated pockets of high temperatures," Mr Absher said. He said a film applied to the hotel's exterior had stopped 70 per cent of rays being reflected, but conceded this had not been enough.

Designers are now working to address what he called "solar convergence", he said.

Well, these are the reported news. We facade guys are aware since some time of similar situations, always located in hot areas of the world. This was up to now called a concave mirror effect, or simply hot spots, although death ray sounds much more interesting!

Why does this occur? And how to avoid it?

Why does a hot spot happen?
The reason is simple: modern glass with solar control coatings has a rather high solar energy reflectivity. Most of the radiant energy arriving from the sun to the outer glass pane gets reflected to the outside (instead of crossing the glass). This is a desired effect to avoid too much overheating inside the glazed spaces.

When the glass surface is flat or convex, the reflected radiation is dissipated onto the atmosphere. But things change when the outer glass surface is concave. Then, depending on the curvature radius, sun rays can concentrate in certain points along the day, varying with the sun position. If these points are located in the air surrounding the building, nobody will realize about them. But, if one of the concentration points (the foci of an ellipse or the center of a circle) falls in an area where there is something sensible to extra heat, then we see the consequences. There is a very clear example in Milan. Sun rays coming from the new headquarters of the Lombardia Region in Milan are overheating and deforming the PVC roller shutters of the neighbouring buildings, as shown in the image below from La Repubblica. The problem has been there since summer 2009. You can see more images at the picture gallery from the newspaper.

How can we measure it?
A pyranometer is a sensor that measures broadband solar irradiance on a planar surface. What a pyranometer reads is the solar radiation flux density (in W/ m2) from a field of view of 180 degrees. If solar irradiance data in a certain area are clearly higher than the average solar radiation in the region, the pyranometer can check it and measure it. After taking a number of measurements along two-three days we come out with a 'plan of hot spots': a distribution of unexpected solar radiation values, measured in flux and in surface temperature. So, knowing if Mr Pintas, the lawyer from Chicago burned at the Vegas hotel, was right or was exagerating would take around three days work with this device.

And how can we avoid it?
This is difficult once the glass concave surface is in place, because the owner is not inclined to change the building shape at this stage. The obvious solution is to avoid concave surfaces with highly reflective glass. So, the typical way out of the fuss is to add a film onto the outer glass face that reduces the energy reflectance.

A reflective glass can have an energy reflectance value of 40%, which is really high. This is the appearance of a magnetronic or pyrolitic 'mirror glass'. Luckily architects don't favour this appearance nowadays (except in Vegas, Dubai or Shanghai, where the problem is most common). The funny thing of the building in Milan - which is not concave, but convex - is that the effect is accentuated because there are several glazed walls, all with a double skin curtain wall. The external film can reduce the reflectance to a value below 15%, which is the typical energy reflectance of a non tinted - non coated double glass unit. Values as low as 8% can be achieved. It goes without saying that energy does not disappear: if it's not reflected, it must be absorbed, heating the outer glass pane. This can have two further consequences: first, the facade becomes a heat radiator to the internal space in summer (a glazed frying pan). On the other hand, the high temperature of the outer glass, combined with some external shadow (if this exists), can break the glass unit due to 'thermal shock'.

This is a well known problem. The way to avoid it is not using annealed glass, but heat strengthed or toughened glass on the outer pane - the one with the highest heat absortion due to coatings or tints. The problem with the post-applied film is that the extreme temperature difference (between the sun-hit and the shadowed parts of a glass) increases, and it can affect the inner glass pane as well, which is usually not thermally treated. So, before applying any anti-reflective coating, our colleagues in Vegas should better do some thermal calcs, or they would get rid of hot spots at the cost of having glass breakages at the hotel rooms in the near future.

We can of course predict if a certain building shape can create hot spots or not during design stage (using 3D modelling tools), and then adjust the building shape or the glass reflectivity to avoid them. I would strongly recommend to do it, or we will have more lawyers coming to us in the future. The existance of "death rays" is official now...

Introduction to Architectural Science

2010-09-26T20:46:00.008+02:00

Introduction to Architectural Science
Steven V Szokolay is an Australian architect and energy / environmental consultant who has worked in Sydney and London, and teached in Liverpool, London and finally Queensland. In this university he was the founding director of the Architectural Science Unit, as well as Head of the Department of Architecture. He is now retired.

This book is a great introduction to the facts, concepts and numbers of heat, light, sound and energy applied to architecture. The second edition from 2008 is the most recent one. The reader can be a practising designer or an undergraduate student; both will benefit from a clear presentation of facts, examples and data sheets. But the best in my opinion is how difficult issues are treated in a way that sounds as if they were being taught for the first time. Just one example: the description of glare (part 2.2.4, page 148). Szokolay aptly describes the differences between glare due to saturation and glare due to contrast, as well as discomfort vs disability glare. Another clear definition is that of daylight factor (part 2.4.2), also belonging to the lighting chapter. But probably the most useful part of the book is Part 4, Resources. Here we can find the basics of energy, renewable energy, energy use in buildings, water, waste, and sustainibility issues. Short and to the point.

Szokolay has also co-authored with Andris Auliciems a 60 pages booklet on thermal confort. The thesis is very attractive: nowadays lifestyles, clothing, technology in building construction and microclimate controls have tended towards homogenizing indoor environments to which humans are exposed. These developments may be driven by market forces, but the result is that humans are becoming adapted to a very narrow band of conditions. This may be a threat to our survival as species: within a changing environment, survivability is greater among the adaptable than the adapted. Which trend is being favoured by technological development and thermal design?

The booklet is available on the net. Do yourself a favour and have a look at it here: Thermal comfort

Metal curtain walls

2010-09-25T22:01:00.138+02:00

One more example of a great old document, this time from 1955 and related to a then start-up facade system, the metal curtain walls in the United States.

This time it's a book (fully available to us thanks to the 'make no evil' Google guys) with the title 'Metal curtain walls'. It is a compilation of the papers and discussions presented at a conference in Washington in September 1955, organized by the Building Research Institute, then a division of the National Academy of Sciences.

Let's start with the obvious: this conference seems to have been a well organized event, the presenters were among the best available specialists at the time, and the response of the public was overwhelming, judging by the number of companies and experts that attended the conference. It was definitely a good time to talk about the matter. Ten years after the end of the war, and just one year after the Lever House opened at 5th Avenue, there was a lot to say and to learn about curtain walls.

The presenters at the conference came from different grounds. There were architects, some big firms and some from academia. Among the former was Max Abramovitz, partner at Harrison Abramovitz in New York and responsible for the planning process of the United Nations headquarters in Manhattan between 1947 and 1952. There was also a partner from SOM, describing the firm's design method for curtain walls at the Ford Motor headquarter in Detroit. The result of an investigation from the School of Architecture at Princeton University about stainless steel curtain walls (conducted in 1954) was also presented.

There were several specialists from different manufacturing companies and some other experts on thermal and acoustic issues. One presentation discussed the role of curtain wall erectors. It is surprising to see how little things have changed in this regard: the poor chaps who installed facades were experiencing the same problems and showing the same clear logic as their equals do today.

Poorly insulated curtain walls have a two times better U-value than non-insulated brick facades. It all depends on the comparison you select to do...

The general impression among the panelists was that curtain walls were going to be the next big thing in facades design and construction for the years to come. They were damn right. One might expect here a lot of naive comments on the advantages of the new technology. Instead, there was surprisingly very few self-praising; quite the opposite, presenters with different technical backgrounds were rather clear in assessing the many problems still unresolved for lightweight cladding.

It seems that at the time architects and owners had fallen in love with glazed facades, whilst contractors and specialists seemed already worried about the limitations of the technology in terms of thermal & acoustic insulation, air tightness, water leakage, metal corrosion and coating durability. The summary of a survey on metal cladding panels, conducted that same years among owners and contractors, shows it cristal clear. Only 2.5% of building owners were dissatisfied, while 13% of contractors would not recommend using curtain walls again. See the details here below.

Things were bound to change in the years to come, with owners becoming less and less interested in curtain walls - but this was still 1955. The Seagram Building details were at Mies' desk by then, and Tom Wolfe had not the least idea that 25 years later he would be writing 'From Bauhaus to our house'.

The architect's view
Max Abramovitz's text is very interesting. We are literally attending to an architect's explanation of modern architecture provided to an audience of builders and manufacturers. He could be outspoken and not too academical. He started saying that the idea of curtain wall was not new, but a development of wooden skeletons and non-bearing stone veneers or other lightweight walls. He then described the factors that made curtain walls so appealing to architects. The list deserves a quotation:

The dry wall, allowing facade construction to proceed even in wet and cold weather.
Lightweight, saving in construction manpower and load to support.
Larger units, thus reducing the number of joints in the facade. For him joints were an architect's headache: the less of them the better.
Non-corrosive and fire resistant materials, that is, metals. A curtain wall wasn't more fire safe then than today, but architects have always found it difficult to distinguish between fire reaction and fire resistance.
Prefabrication, very neatly expressed: 'We will get more construction for our money'.

The facade contractor's view

My favourite presentation, though, is the one given by the erectors representative, a such Mr. Collier, president of a facade contracting company. Among many interesting things in his text, there is a lateral comment that struck my attention. Remember, we are in 1955. Weather proofing concepts such as rain screen or pressure equalization had not been identified yet, and do not appear along the conference proceedings. On the other hand, selants based on silicone had not been developed at the time. Facade joints were caulked with Thiokol at best. Mr Collier, though, was not happy with the then predominant solution of open joints in lightweight facade panels to allow for movement, with an internal air and water sealed barrier. He prefered, based on his personal experience, an externally sealed wall to prevent water to come into the building in the first place. Well, of all the predictions made in this interesting book, the preference of Mr. Collier for externally sealed facades was going to become the mainstream solution in the US, as soon as silicone became available, and lasting until today. Dow Corning was going to be more convincing to American builders and architects than the rain screen principle.

We Europeans laugh at the Americans love for sealed joints in stone or aluminium veneer facades. But apparently Americans prefered the reasoning of Mr. Collier, an entrepreneur, to that of G.K. Garden in 1963, a researcher from a Canadian building institution and the father of the open joint design in modern facades. And they still do...

The facades of the future

2010-09-20T21:14:00.060+02:00

This is a post under construction. In fact, it may be under construction for years, since its theme will always remain open. What are the key indicators of the facades of the future? What will matter - and what won't - in relation to how we design building envelopes today?

The following is a list (yes, I love lists) of the issues that will define facades design in the near and longer future. Let's put a time lag to this: by 2020? That's rather soon. 2030 is better: twenty years from now.

1. Image:
a) Media facades - they tell us a changing message. See below and here for a video of Ned Kahn's facade moved by the wind:

Ned Kahn, Technorama facade - Swiss Science Centre, Winthertur

N Building, Tokyo. Terada Design and Qosmo - The facade is covered in QR codes. Clic a pic of this building and you will get info of all its inhabitants in your mobile.

b) Interactive facades - we can ask them for something, and they will answer. See above and here for more information.

c) Dynamic facades - they will move, in order to perform better, but also in a way we will consider aesthetically pleasant - as it should be: utilitas & venustas. See below and here for the video.

Kiefer Technic Showroom, Giselbrecht + Partners - The louvers move constanty depending on the day and light conditions, and on the inner use of the rooms.

2. Performance:
Future facades will be extremely performant. We have almost reached the limit of tectonics nowadays (what can be done to make any element structurally resistant and stable) but we have just started to grasp the surface of the non-tectonic issues (what can be done to improve the capacity of building elements to reduce thermal transmission, reduce emissivity, limit noise transmission, avoid air and water penetrations, maximize visible light transmittance whilst blocking UV and infrared rays, etc etc).

We are so behind in non-techtonic related issues that there isn't even a name for those (let me suggest one: herkonics, from 'herkos', building fence and interface in Greek)

3. Sustainability:
If a building envelope performs well in terms of energy, it should already be sustainable, right? Well, in the future that won't be enough. As long as we will achieve zero-energy buildings (by both passive and active means) other issues will become more important than what they are now. That's the case with materials carbon footprint, re-usability of elements as per the cradle to cradle mantra, water retaining and reusing, etc.

4. Buildability:
Facades will always have to be fabricated, transported and installed on site. That must be made in a more efficent way - to reduce their carbon footprint, to reduce time, to reduce costs, to reduce uncertainty and risk of malfunction. This is really difficult and will consume the 20 years period I have given for this list to become reality. Can you imagine a robotic factory? You surely can. Now try to imagine a complete robotic jobsite!

Joints and interfaces between facade elements will become even more critical in the future. Again , this is science fiction, regardless the fact that we have been dicussing it since the 50's.

5. Post-occupancy:
This involves first of all facades design that allows user comfort, adaptability and dynamic response to different needs.

Second, it means that our envelopes should be easy to maintain, but really so; reducing the costs, the effort and the spill of water and consumables we need now. And easy to replace: when something breaks or underperforms, the system detects it and the substitution is done together with the cleaning... Sounds futuristic, doesn't it?

And, last but not least, durable facades. This is the Holy Grial of the whole story. Sustainable in Darwinian terms means lasting. Our facades today are creationists, not evolucionists. We act like gods, but gods without the power - and our 'creatures' disappear swallowed by the harshness of the real world. Some day our building envelopes will again, as in the past, be durable. It will definitely take time: I don't care if it's more than 20 years, as long as the trend goes in that direction.

Facade - structure tolerances: the buffer zone

2010-09-15T20:04:00.017+02:00

A visit to the Arup central library in London is always a great experience. The other day I found this book, out of catalog and unavailable in Amazon: 'Interfaces - Curtain wall connections to steel frames'.
One of the interesting sections is devoted to discussing the tolerances that a designer should always consider between the plane of the building facade and the alignment of the structural steelwork. For the purpose of this post, the main structure can be steel or concrete, and the lightweight facade can be a curtain wall or any other system.

The idea of writing about this issue comes from an architect with whom we are working these days. The project name and location aren't relevant. Our architect wanted to stick the curtain wall plane to the front plane of a steel column, with no space in between. This would surely make a nice detail as shown on a Scheme Design drawing: all flush and neat. We have had to go some length to explain something quite clear to us facade engineers, but obviously not so to architects in general. The point in discussion was the need to consider a separation between the main structure and the inner plane of a curtain wall. Why is it necessary, and how big should that space be?

Let's go with the why first
The structure of a building is not built by Swiss watchmakers. For example, the edge of the steel decking is is often set out from the centre line of the steel beam. In a concrete structure, the formwork is positioned in relation to the axis of the adjacent columns. Both are not proper methods - the setting out line should be the main axis lines at each floor. The result is that dimensional variations in the positioning of beams or columns are transferred to the alignment of the edge of slab. Add movements of the formwowk (in case of concrete) and you have a wobbly line instead of a perfect vertical plan.

Bosch CST Berger laser

The same, at a much smaller scale, happens with the curtain wall or lightweight facade installation. Facade contractors use accurate positioning tools as laser beams for the setting out of their lines and brackets. The image to the left is a high quality laser level, capable of self-leveling in horizontal, vertical and plan. The reader unit can find the laser beam as far as 800m away. But its accuracy is not perfect: +/-3mm vertical misalignment every 30m. Add small mistakes when marking lines with chalk on the concrete slab, bracket positioning and profiles drilling, and there you go with a certain degree of variation.

Now the dimensions
How big should the tolerance space be? What I liked about the book above is the way the authors divide the requested space - the total tolerance - in three areas:

Tolerances which define the zone within which the main structure should be built. Their value depend on the national building codes, the material, the quality of workmanship and the building size and shape.
Tolerances to absorb the misalignments of the facade elements in relation to their theoretical plane. These are smaller than the first ones, a rule of thumb is three times smaller.
A 'buffer zone' between the two tolerances above. This is an additional contingency against excessive dimensional errors. In practice, all structural frames exceed their specified tolerances at least in some points of the structure.

The buffer is the way to avoid breaking arms and legs in order to fix a facade in every building. But remember, they are not intended to be a relaxation of the structural specification (or of the facade installation), rather they are a recognition that sometimes work does not go as planned - even in Switzerland.
The drawings below show, nº 1 for steel structure + curtain wall and nº 2 for concrete structure and precast, my personal rule of thumb for a general structure - facade tolerance. The three areas are shown in each case.

Steel structure plus curtain wall tolerances

Concrete structure plus precast concrete cladding tolerances

The buffer must not be excessively large, since fixing details which have to trasfer the cladding loads across the zone will themselves become significant and costly structural elements. As the cladding contractor effectively carries the cost of the buffer, the designers should consult him to assess a realistic dimension, at least in special cases.

You've got the point now. Let's assume this is too detailed to remember; what should be the real rule of thumb for architects? Easy: the theoretical distance between outer structure and inner wall should be 60mm for curtain walls, 70mm for precast. This is easier to keep in mind.

Matteoli: Water and air tightness of external windows

2010-09-11T20:09:00.016+02:00

This post inaugurates the recovery of old documents from which we must still learn a lot: oldies but goldies. The first one is almost 40 years old, it is written in Italian and was published in 1971. Its title is 'Tenuta all'aria e all'acqua dei serramenti esterni'. The author is Lorenzo Matteoli.

Why was it important?
Italy in the 70's - as all Southern Europe - had very low quality windows. The typical window frame was made in aluminium, although there were still many hot formed steel sections. Their water and air tightness design was based in the steel sections of European 1930's suppliers: the best ones had two gaskets, one on the outside and one on the inside of the frame.
Lorenzo Matteoli was leading the testing laboratory of the Istituto di Elementi Costruttivi, a branch of the Architectural School at the Politecnico di Torino. By 1971 his team had conducted six years of window testing, and he had extracted some design principles to improve the window performance. I assume he was aware of the work by O. Birkeland and G.K. Garden about rain-screen and pressure equalization, appeared in 1963-64. But in my opinion the bulk inovations of his paper came from analysing the window tests conducted at the laboratory.

After its publication in 1971 this paper became inmediately influencial for facade contractors and window suppliers, but it was especially followed among aluminium extruders who had window profiles to sell. The aluminium extrusion companies were big conglomerates with very basic products, which they had to improve if they wanted to win in the market for new housing, then booming. This paper explained the new idea of pressure equalization and how it could be applied to windows, and it did so starting from scratch. The text is so basic that there are no drawings or references to central gaskets at all. But the concept of a gasket located in the center of the frame and not on the outside was already being applied in Germany, and with Matteoli's help it became obvious what a central gasket could do, and why it was better to have an external open joint between the frame and the sash.

But what did it say?

1. The water running along the outer surface of a window...

Matteoli's paper has an additional advantage: it can be understood almost without reading it, because it comes with a number of hand sketched drawings and captions that are the real summary of the paper. I assume not everyone reads Italian, but please have a look at the first four sketches with translated captions here below, and judge by yourselves.

2. ... through vertical and horizontal joints...

3. ... gets in contact with the outer gasket. Since Pe is higher than Po, water tends to come in, helped by capillarity processes...

4. ... by pressure differencial and by air movement inside the intermediate chamber, until it reaches the inner gasket where, helped again by capillarity and pressure differencial (Po is higher than Pi), it finds a way to the inside.

Now a personal comment

I first found this document while I was studying architecture in Madrid, at the school Library, together with other oldies as the curtain wall series published by Folcrá in the seventies. It didn´t make an impression to me then, but some years later I was going to be working for one of those big aluminium extruders: Hydro Aluminium, owner of the window brand Domal. At Hydro's technical department near Milan, led by Massimo Dampierre, this document appeared again. They told me the story of the evolution from the two gaskets to the central gasket, the move from punched hinges to a channel where all accessories could be fitted and removed (the 'European channel'), the birth of thermal break profiles. The Italians had coined a hip name for the new family of windows that became popular in Southern Europe: these new windows were 'systems', just because their elements were interchangeable. You can use the same glazing bead profiles, gaskets or acessories for different window types and it works, saving time and reducing stock at the window manufacturer. Now it's pretty obvious and has become standard, but it all started at a hidden testing place in Turin...

A real pleasure to read. The whole document is just seven pages long: go to the link and check your Italian!

From Wigwarm to Ikea (houses)

2010-09-10T19:21:00.032+02:00

'I find it incredible that there will not be a sweeping revolution in the methods of building during the next century. The erection of a house wall, come to think of it, is an astonishingly tedious and complex business: the final result is exceedingly unsatisfactory'

Wells, H.G. 'Anticipations of the reaction of mechanical and scientific progress upon human life and thought', Chapman, London 1901.
Taken from Alan Brookes, 'The turning point of building'

Who said H.G. Wells was not a man of vision? Some might argue, though, that Mr Wells failed by not predicting the arrival of mass housing prefabrication systems in the 20th century. Well, if that was the question, I'm afraid the answer is even tougher: he didn't have to predic anything, because house prefabrication was well known by the turn of the century. And again, if he new it, he didn't fail in his predictions at all: prefab houses today are as much 'the next thing to come to building' as they were in 1900. Only that we are still waiting for this to happen...

One of the first succesful examples of prefab housing in the USA is the E.F. Hodgson Company, active in Dover, Massachusetts between 1894 and 1944. Their houses came under the brand Wigwarm. The word is a mixture of wigwam, an Indian tent similar to a teepee, and warm. Its meaning: quick to assemble but comfy.

A Hodgson cottage in Dover, MA, as appeared in the 1935 E.F. Hodgson Catalog

One of the remaining Hodgson houses, built in 1940, in pristine condition inside and outside

The Wigwarm construction was a framed house, lighter than a standard timber frame construction, based on several timber sections fastened together with key bolts of special design. With just a blow of a hammer the wedge key tightened up the bolt, saving time during erection or dismantling. Frames were covered with a very heavy waterproof fibre or lining and then with a rabetted siding. The basic modulus for the houses was 6 x 12ft (1.80 x 3.60m). Mr Hodgson didn't just prefabricate houses, he also sold brooders, tool houses, dog houses, car garages - there is one in the top image to the right - or, during war periods, barracks for the military. In the '20s and '30s you could see Hogson houses in places as Europe (Belgium and Italy), Israel, Africa and South America.

Was it a commercial success? It really was, and it was simply based on selling by mail. A response to an ad in a newspaper would get the potential client a full catalog with photographs, floor plans and comments by satisfied customers. The company did not survive its founder: Mr Hodgson, without a son to continue the business, sold it in 1944, four years before he died.

The story is surprisingly similar to today's prefab, portable houses through catalog: the brand new Ikea/BoKlok house. Even the look is familiar. BoKlok, the webpage tells, builds homes for ordinary people who want to have money left over. But the idea for this house was born in very different circumstances, as a dialogue between IKEA and Skanska chairmen in 1996. A retailer and a construction company sharing forces to create affordable apartments. Up to now they have sold more than 4,000 houses in five countries, and the idea is booming, from Scandinavia to Germany to the UK.

Who knows, maybe now it's the time for the sweeping revolution in the methods of building that H.G. Wells was asking for: his period of 100 years is finally over...

Updating a landmark: from Rome to Illinois

2010-08-27T13:49:00.008+02:00

Two architectural masterpieces have been restorated recently or are under a process of restoration: Mies' Crown Hall at the Illinois Institute of Technology and the Panteon in Rome. What can we learn from a facades perspective? Is there any connection between these two interventions?

The Crown Hall is the jewel of the crown in the IIT masterplan. Completed in 1956, it houses the College of Architecture at the Illinois Institute of Technology in Chicago. A clear-span structure, its roof is suspended from four solid plate girders above. Within the column-free structure is a universal space, 220 feet by 120 feet wide by 18 feet high, that provides a completely flexible environment, often described as a large one-room schoolhouse.

In Crown Hall, Mies created an edifice that clearly reflects its technology. The plate girders are immediately visible to the observer, and they are seamlessly integrated into the steel columns running outside the glass enclosure. Smaller vertical steel members frame the large sheets of glazing. Except for a steel and travertine terrace providing access to the raised first floor, there are no other exterior features. Crown Hall is, as Mies would say, “Almost nothing.”

How do you retrofit a building which is so next to nothing? It definitely took more effort than one might expect initially.

http://www.iit.edu/giving/mies/about/restoration/crown_hall/restoration_reports.shtml
http://www.lynnbecker.com/repeat/mies/miesresurrected.htm

The Panteon, against what one might imagine, was not erected by Agrippa, even if his name appears at the front of the temple. Agrippa did commision a former Panteon to adore all Roman gods in that place by .... ad, but the building got fired and was demolished. The Panteon we admire today was ordered by Adrianus, a great Roman emperor of Spanish origin, in .....ad.

Wind loading: science or myth?

2010-08-21T14:32:00.018+02:00

Three researchers of the TU Delft have written a very interesting paper on the topic of facade and roof wind loading, with the title: 'Towards a reliable design of facade and roof elements against wind loading'. The paper, published in 2004, is a good starting point for some comments on the matter.

Geurts, van Staalduinen and de Wit very rightly point out that 'current building practice, including the building codes, is still not able to safeguard against local wind loads for every situation'. Wind loading codes, according to the paper, fall short on three main issues:

Many buildings are not covered by the typical square or rectangular plan shapes appearing on the building codes. In these cases wind tunnel experiments are the natural option, but an accepted and clear procedure on how to conduct and analyze wind tunnel measurements is not available yet.
Pressure equalization plays an important role in the design of roof and facade elements, but it may increase the total wind loading. Such effect is not well covered in our codes.
The effect that neighbouring buildings have on the local wind loads is not included in our standards, and there isn't an agreed procedure on how to measure it in a wind tunnel.

To be continued...

U-value: a not so well-known concept

2010-08-20T17:56:00.022+02:00

Most of us have a general idea of the concepts of U- value and g- value when dealing with thermal properties of facades. This post presents some issues not so well known about U-value. A future one will deal with g-value and finally a third one will unify both of them under a building physics perspective.

Low U-values of two walls of Jukka Talo, a Finnish supplier of prefabricated timber houses.
Left, 318mm + 48mm mineral wool insulation; U-value: 0,11W/m2ºK.
Right, 318mm mineral wool + 50mm polyurethane insulation; U-value: 0,10W/m2ºK.

Let's start with the basics we know already.

U-value, or thermal transmittance, is the heat flow density going through one m2 of a specific wall element when both sides of the wall are subject to a temperature difference of one ºK. Heat is a form of energy and thus heat flow is measured in Joules/second, that is, in Watt. According to this definition, U-value is measured in W/m2ºK.
Another definition (by Limb in 'Air infiltration and ventilation glossary', 1992) describes U-value as the heat flow transmitted through a unit area of a given structure, divided by the difference between the effective ambient temperature on either side of the structure, under steady state conditions.
That is, the interaction between the wall and the outer / inner air layers, the thickness of the wall or the fact that the wall has one or several layers are all combined within the U-value: what it tells us is the amount of heat that gets through a certain wall per m2 per ºK, as simple as that. Or not that simple?

The U-value of a glass pane is determined in Europe by calculation according to EN 673 or by measurement according to EN 674. Under the same boundary conditions, calcs and measurements result in very similar U-values. Funnily, the American code for glass, ASHRAE/NFRC, yield a slightly worse (that is, higher) U-value than the European standards. The difference can be around 0.1 - 0.2W/m2ºK. Furthermore, the ASHRAE U-value is separated into winter and summer conditions.

Does U-value measure convection, conduction or radiation?
It is clear that g-value refers to solar radiation through transparent materials such as window glass surfaces. It does not measure heat exchanges due to conduction or convection. What about U-value? Does it only measure heat flows due to convection and conduction, or does it also measure radiation? Interestingly, the primary mode of heat transfer impeded by thermal insulation in a facade is convection, but in fact U-value measures heat loss by all three heat transfer modes: conduction, convection, and radiation:

Convection occurs because of changes in air density with temperature, creating a movement of the air that transfers heat. Insulation materials greatly retard natural convection in air filled cavities, so that convective heat loss is significantly reduced.
Conduction implies heat being transferred between substances in physical contact. The mineral wool or foam required to prevent convection slightly increases the heat conduction in a cavity compared to still air, because the insulation density is higher than air. But, roughly speaking, the conduction effect of heat transmission increases with density. Insulation materials are in general low conductive materials because of their low density.
Radiation is the transmission of heat through space by the propagation of infrared energy, without necessarily warming the space between. Radiative heat transfer is minimised by having many surfaces interrupting a "clear view" between the inner and outer surfaces of the wall. Remember: radiation is best transmitted in total absence of matter such as in interplanetary space, as the sun demonstrates every clear day. Finally, radiation is also reduced by low emissivity (highly reflective) surfaces. Thermal insulation, with its foamy or capillary structure, behaves as a multiple filter to radiative heat.

Thermal conductivity of common materials
Thermal conductivity (expressed by the Greek letter lambda) is a thermal property of a material, of its ability to conduct heat. It is measured as the rate of heat flow (W) over unit lenght (m) through that material over unit area (m2), caused by unit temperature difference (K): W.m/m2.K, by cancellation: W/mK. The lower the conductivity of a material, the better it acts as a thermal insulator.

Glass has a thermal conductivity of 1.05W/mK. Is this high or low? It is rather high, although very small if we compare it with metalic materials as steel (54), aluminium (250) or copper (401). Glass is a rock, so its thermal conductivity is not too far away from a typical stone (1.7 to 3) or standar concrete (1.7). Dry earth has a value of 1.5W/mK. A solid brick (1.3) is more conductive than a brick wall (0.69) because the latter has air in the hollow ceramic bricks.

What about insulation materials? Air conductivity is 0.024W/mK, a very low one, even less than that of EPS or XPS (0.03 - 0.033) or mineral wool (0.04). Cork (0.07) and cotton (0.03) are also more conductive than air. Only polyurethane foam (0.02) has a lower conductivity than air, but not that different. By the way, snow is a good thermal insulation in winter. When the outer temperature is below 0ºC, snow lambda is around 0.05 to 0.25W/mK, depending on its density. Water is much worse as a thermal insulator (0.58). High density wood does insulate: 0.12 to 0.17, not bad.

Why do we use insulation materials instead of just air cavities? Clearly because it is difficult to have the air still and quiet in a chamber, and avoid the convective currents. Is there a material with a thermal conductivity lower than air, but not suffering from air convective currents? Yes, and these are the noble gases: argon (0.016), krypton (0.0095) and xenon (0.00565). More about them right now.

What is the role of air thickness and infill in a double glass unit?
The insulating efficiency of a standard double glass unit depends on the thickness of the air space between glass sheets. Too little space results in conductive heat loss: the inside surface of one pane cools the surface of the other pane. Too wide a gap results in convection current losses: air begins to circulate because of temperature differences and transfers heat between the panes. Glass sealed units achieve their maximum insulating values using an intermediate space between 16 and 19 mm.
This is fine, but not enough. Reducing the U-value from 2.9 down to 2.6W/m2ºK is fine, but it represents a 10% reduction only. Why do we get an even lower thermal transmittance (and thus a lower U-value) by replacing air with argon in a double glass unit or in a high quality foam insulation? Which one of the three heat transfer modes is retarded here?

Replacing the air in the intermediate space with a heavy gas, slightly denser but much more viscous than oxygen and nitrogen, is helpful because its higher viscosity reduces convective heat transfer. Argon (whose thermal conductivity is 67% that of air), krypton (with a conductivity 2.5 times smaller than air) or xenon (4.2 times smaller) do increase the insulating performance of the whole glass unit because of their reduced convective transmission besides their lower thermal conductivity. Argon, krypton and xenon are used because they are non-toxic, clear, odorless, chemically inert, and commercially available, but their cost grows exponentially with their alphabetic order. That is why argon is the one most commonly used, always in combination with low-e coatings. By the way, the more effective a fill gas, the thinner its optimum thickness becomes. For example, the optimum thickness for argon is lower than for air, and lower for krypton than for argon. This is good to know because these infills are expensive. All considered, an air space of 15mm with argon at 95% or more is a very good selection if you have to reduce your U-value in glass. But remember to add a low-e coating as well!

Is U-value really constant?
More tricky things: the U-value is calculated under standardized conditions, usually under an air temperature of 20ºC inside and 10ºC outside, a surface emissivity of 0.9, a 50% humidity and an external wind speed of 4m/s. Air in movement should have a certain influence on the thermal resistance of an outer surface: wind increases the interaction between the wall and the outer air layer, and conductivity is higher. But the air temperature? Does this mean that U-values vary with temperature? Yep. Now, does U-value increase under cold or hot temperatures? Does U-value increase or decrease with a strong wind? Which of those two variables is more important?

Air movement and temperature inside and outside the wall do affect the surface resistance values of the wall. Let's forget the inside face of the wall: its temperature and air movement variations are too small to affect the U-value. The surface resistance is the combination of a convective coefficient and a radiative coefficient. The convective coefficient depends directly on wind speed, and its range of variation is huge: convection is 'pushed' by a 10m/s wind speed eleven times more than under a total still air. The radiative coefficient varies with temperature, but not that much, just +/- 20% under extreme external temperatures. If we are in Norway and the outer temperature is -10º, the external surface resistance of the wall will be 0.042 ºKm2/W instead of 0.04. If we are in Saudi, +40º outside, expect something around 0.038 ºKm2/W

To cut a long story short, what are the parameters that can really modify the mean U-value of a wall?

External temperature has a very small influence. It does not affect at all opaque, well insulated walls. For glazed walls the variation is also very small: a curtain wall with a mean U-value of 1.75W/m2ºK at +10ºC outside will have the same value at -10ºC outside, and will raise to 1,76W/m2ºK when the outer temperature is +30ºC.
Emissivity of materials can have an influence, and it varies depending on the material. We know it is critical in glass (lowering its U-value from 2.5 to 1.7W/m2ºK, for instance). When a material has an intrinsic low emissivity it is difficult to make a difference on the U-value if we reduce it even further. That is the case with aluminium: reducing its emissivity with special coatings has a very small influence on the mean U-value of the wall (especially if it's a glazed curtain wall).
Wind speed has an important influence if our wall is a glazed facade, and it doesn't affect the mean U-value if it's a well insulated opaque wall. A curtain wall with an R value of 7 ºKm2/W (that's a high performant curtain wall) will have a mean U-value of 1.75W/m2ºK. Now comes the surprise: if wind speed moves up from 4m/s to 10m/s (nothing extraordinary for curtain walls, especially in high rise buildings) the mean U-value due to wind speed raises from 1.75 up to 1.82W/m2ºK. That's not the same thing!

U-value matters, but so does air permeability
Please remember this: the insulation quality of a wall is affected by other factors not addressed by U-value classification. Although the U-value laboratory test captures the effects of convective loops within the insulation, it cannot measure the amount of air leakage through a real wall assembly once the insulation is installed. The rate of air permability in a wall is affected by:

the density and continuity of the insulation,
the presence or absence of an air barrier in the wall assembly,
the wind speed, and
the pressure difference between outside and inside the wall.

Because of these factors, a wall assembly insulated with fiberglass or mineral wool blankets will usually perform worse than a wall assembly insulated with a continuous sprayed foam, even when the foam has the same U-value as the blankets. The difference is due to the spray foam’s ability to reduce air leakage, not to any difference in U-value between the two materials.
To obtain the best performance from fiberglass or mineral wool insulation, the US Energy Star Homes program requires most fiberglass-insulated framing cavities to be enclosed by air barriers on all six sides. It makes sense, but it’s hard to achieve on site.

Cold bridges or thermal bridges are clearly an interruption to the continuity of insulation and thus an increase of the general U-value of the wall. But there is a less obvious type of cold bridge, shown above, known as thermal looping: an air gap of more than 1mm between the insulation and the inner wall leaf allows air circulation, creating convective currents and leading to a significant reduction of the overall U-value. This was first presented by Jan Lecompte in a paper of 1990, named 'Influence of natural convection in an insulated cavity on the thermal performance of a wall'. How many of us know about it, and take care of it in our details?

Well, somebody knows it, but not too well. The standard EN ISO 6946:2007 has an annex D called 'Correction to thermal transmittance'. One of the corrections covers thermal looping. I don't like the way it's done though, because it does not include the gap thickness as a variable, and the so-called correction is too small: you just have to add less than 0.04W/m2K. In this case, sorry to say chaps, calculations don't match measurements!

Some suppliers of radiant barriers or spray foam insulation, well aware of these issues, tend to imply that U-value measurements are meaningless. U-value is of course a very useful measurement, but just because you know a product’s U-value doesn’t mean you know everything necessary to predict the real heat flow through a wall or a roof. No one has yet invented a magic number that replaces the requirement for designers to study and understand building physics principles.

Does radiant heat pass through insulation?
We have just mentioned radiant barriers. Another tactic employed by some suppliers of of these products is the idea that conventional insulation materials - sometimes called mass insulation - allow radiant heat to pass right through them. Some radiant barrier brochures happily state that 'mass insulation is transparent to radiant heat'. The implication is that a layer of aluminum foil is always necessary to prevent radiant heat from traveling like radio waves right through a deep layer of cellulose, foam or XPS.
In fact, most mass insulation products do stop most of the radiant heat flow. Radiant heat easily travels through air (for example, from a wood stove to your nearby skin) or a vacuum (for example, from the sun to the earth). But radiant energy can’t travel that easy through a denser material. When radiant heat hits one side of a deep layer of insulation, only a tiny percentage of that radiant heat manages to miss all of the fibers in the insulation blanket and emerge unscathed on the other side.

The fact that heat flows through a layer of insulation doesn’t mean that the insulation isn’t working. By definition, insulation slows down heat flow; it doesn’t stop it. Heat will always flow from hot to cold. The more insulation and the lower the air permeability, as we have seen, the slower the heat flow.

Transmittance (U-value) and air-to-air resistance (Ra-a)
The reciprocal of the U-value is the air-to-air resistance (Ra-a, measured in m2K/W) which is the sum of each of the wall resistances: resistances of the external and internal surfaces of the wall plus resistances of each of its layers. E.g., for a wall of two layers:

Ra-a = Rso + R1 +R2 + Rsi.

The R-value of any homogenous layer is its thickness (in m) divided by the conductivity of its material. Thus, a good insulation material which has a very low conductivity will have a high resistance. Conductivity is a constant for any given material under certain conditions, while R-value depends on the material thickness. That is why most of the insulation materials in the market come with their R-value: each value defines every product (given a certain conductivity and a commercial thickness). Good insulation materials have an R-value of 5, 6 or even 10. These values are not in the SI, but in the typical US unit system: ft2·ºF·h/BTU·in (notice that ·in at the denominator: R-values are usually expressed per inch, to allow for comparison)

American marketed products come with their R-value/in expressed in US units. It takes time to translate them to SI values, now measured per cm. Here is a list of insulation materials with their R-value expressed in US units (per inch) and also in SI units (per cm):

Where can I learn more?
European (EN) and worldwide (ISO) standards have a bad reputation: they are definitely not easy to read. How could they be easy, having been written by a committee? But that doesn't mean they are not interesting, if what you are looking for is guidance or precision.
These are my five favourites in relation to thermal transmission:

a) EN ISO 6946:2007 for opaque elements: walls, roofs and floors.

And its referenced documents:

ISO 7345, Thermal insulation - physical quantities and definitions.
ISO 10456, Building materials and products - Hygrothermal properties - Tabulated design values.
ISO 13789, Thermal performance of buildings - Transmission and ventilation heat transfer coefficients.

b) EN ISO 13370, for heat transfer via the ground.

c) EN ISO 10077-1 for doors, windows and other glazed elements.

d) EN 13947, for curtain walls.

e) ISO 10221, for thermal bridges

My future book about facades

2010-08-20T13:12:00.007+02:00

The first reason for this blog was not to create a blog.

I saw this tool - and still see it - as a way to write and keep track of issues that can be part of a future book about facades design. Writing a book takes a lot of effort and of structured work; to scribble a quick post and develop it later will supposedly be much easier.

What this book should not be:

A list of building examples with nice pictures and an introduction. With all respect, this is the Christian Schittich method (see his Detail facade books), and he seems to have too many followers. Enough!
A manual for absolute beginners. This book already exists. See Facades: principles of construction. Maybe later...
A technical manual. The topic is too wide to add something new. But there must be a technical approach to every issue in the book! Otherwise there would not be good conclussions.
A purely 'design oriented' facade book, helping architects find ideas for their projects. Of course there should be ideas, but it won't be the facades Vogue.
Another greenminded eco book about how important facades are for saving our planet. Again, sustainability matters, but with sense and sensibility.
A collection of innovative facade materials. There are thousands of these as books, webpages and blogs. I plan to do a list of the best ones. It would be great to provide some examples of improper use of materials in innovative facades: being innovative does not exempt a material from being feasible.

This is the list of don'ts. What about the characteristics this future book should have?

Engaging, well written, with an interesting story to tell. This means that the selection and order of topics will be crucial.
Funny. The less you know about something, the more 'professoral' you become. Have you read anything of Stephen Jay Gould, Richard Dawkins, Ian Stewart, P.W. Atkins, Richard Feynman, Oliver Sacks or H.D.F. Kitto? None of these chaps is or was an architect or a builder. They are or were great professionals in their specialties, and they have or had the wit to engage readers, even outsiders to their field. Not many architecture or building technology books are written like that. Mario Salvadori, Eduardo Torroja or Peter Rice did it. Nobody in facades that I have met.
Well illustrated. To me, this means two things: a) each image or picture must be the adequate to illustrate the matter, and b) hand sketches and diagrams are better than colour prints. Images should provide light as in an anatomy treaty, not to conceal or effect as the curtains in a theather stage.
Interdisciplinar. Mixing the conflicting points of view that architects, engineers, facade contractors, materials and system suppliers, code writers, owners, facilities managers and end users have about facades. Conflict is good, it sheds light or at least paves the way to a solution.
Balanced. In the book there have to be bits of theory, history, practice, details, failure investigation, testing, materials science, building physics, mock up definition, acoustics, daylighting, structures, fire safety, resilience, means of access, procuring, building systems, construction methods and so on. The goal is to put these viewpoints against each other, not to prevail one over the others. This is the way good buildings behave.
With a view. The reader will be initially asked to believe that facades design is a discipline where architecture, engineering and building specialist must work hand in hand, with a method, if a proper outcome shall be found once the building is in use. The book will demonstrate that such a holistic approach is not just a myth, but a doable and convenient way of design.

Well, nothing less than that!

Roof selection and details - Carles Broto

2010-08-20T09:11:00.005+02:00

Roof selection and details
The author's name is Carles Broto from Barcelona, but sometimes he signs his books as Charles Broto.

The book is basicly a description of roof systems with many images, some sections, a projects selection and a short introduction to each chapter. It doesn't seem bad as a first introduction to the topic, but I would not rely too much on its accuracy.

Chapter 1 deals with types of roofs - nice details and clear graphic descriptions of each element. For those of us not English native, a good help indeed! Pitched roofs are described in chapter 2, covering monopitch, gable end, hipped and polyhedral roofs. Chapter 3 covers curved roofs, while chapter 4 goes for flat ones, both the walk-on and the ones with gravel finish. Chapter 5 explains the roof/facade systems, so common lately. Other types of roof (such as simmingpool, parking and green roofs) are described in chapter 6. Next one covers auxiliary elements as skylights, louvres, eaves, vents, chimney pots, gutters and drains. The last chapter describes the most common roofing materials: ceramic and slate tiles, bituminous and synthetic membranes, wood, glass and metal.

In summary: a simple writing style, no profound findings, good quality images. The price ($55) looks like a bit high to me though.

Facades: principles of construction - Ulrich Knaack

2010-08-20T08:57:00.133+02:00

Is there a need for yet another book about facades? Yes, if you are looking for a basic understanding of the facade and its technical realization in a more fundamental manner. Facades: Principles of construction is a very simple and well organized introduction about facade design. If you are a student and are interested in facade design and construction - that is, in how a facade works - this is the book to start with.

Professor Ulrich Knaack, the main author, is head of the Chair Design of Construction at the Faculty of Architecture, TU Delft. In 2005 he founded the Facade Research Group and is iniciator of the conference series 'The Future Envelope'. The other three authors are Auer, Klein and Billow. Thomas Auer is a partner at Transsolar in Stuttgart. He specialises in the field of integrated building services. Tillman Klein is an architect and heads the Facade Research Group at TU Delft. Marcel Bilow is a research associate with Professor Knaack at the University of Applied Sciences in Detmold.

The book presents the design process of a facade as a sum of progressive steps. Chapter 2, From wall to facade, discusses the development of today's facades and their typological classification. Chapter 3, Principles of construction, explains the interrelation between the building structure and the facade system. Chapter 4, Principles of detailing and tolerances, covers the generation of technical details for the general solutions defined previously. Topics such as integrated design and building physics aspects of the facade are discussed in chapter 5, Climate and energy. Chapter 6, Adaptative facades, analyses how facades can adapt to changing parametres. Chapter 7, Case studies, illustrates typical and special facade solutions on the basis of selected projects. In closing chapter 8, A look into the future, the authors provide an outlook into possible developments in facade technology.

Mike Davies, the concept of polyvalent wall as drawn in 1981. The layers between the two glass panes were supposed to have a thickness of a few microns.

The problem with facades design and construction, in relation to past eras, is that envelopes have become a complex structure with numerous functions and a difficult technical realization. Thus, the prevailing trend in facade technology is its increased complexity. Two paths of design have tried to answer this complexity: one, the separation of each performance requirement in a specific layer and / or material; the other, the search for integration via adaptability. The real message of this book - and quite relevant for us, regardless we are students or not - is the authors' preference for an integrated envelope instead of a multi-functional facade concept.

In 1981 Mike Davies - while working for Richard Rogers and Partners - formulated the idea of a polyvalent wall in an article signed with Rogers and titled 'A wall for all seasons'. Here, several functional layers within a glass element were to provide sun and heat protection, and to regulate the functions automatically according to current conditions. The wall itself (see the image above) was to generate the necessary energy. As a matter of fact, the label 'Intelligent wall' derives from Davies' concept of the polyvalent wall. His idea, not yet realized, still acts as a driving force for new facade technologies, and many researchers have been engaged in this topic over the last two decades.

Capricorn House, Düsseldorf. Gatermann + Schlossig, 2006

Knaack and his colleagues, following Davies' steps, start by presenting the concept of an integrated facade in a more macroscopic - and realistic - way (see page 100 of the book). It seems reasonable - they argue - to integrate heating elements, air-conditioning and ventilation units, movable shading and other appliances into a facade module. These functions can be combined on the basis of a modular design principle. We could cite some examples where this has been already achieved, as in the Capricorn House in Düsseldorf (image to the right), where decentralized ventilation components and lighting are integrated into the enclosed facade elements.

Functional concept of the integrated envelope according to Knaack: loadbearing, insulation, water and air tightness, ventilation, energy generation, radiation control and transparency, all in one element.

But later in page 130, when discussing the future facade trends, the authors come up with their search for the almighty facade: a further integration with the building services and the structure of the building, all in one. This is the Holy Grial of tomorrow's facade, but it won't be easy to achieve. In their own words:

The future facade has to be based on an integrated concept, i. e. it has to combine and regulate functions that in some cases might contradict each other. (..) This leads to the question of how the facade should be structured - all in one layer or stacked on top of each other. The smaller the components, the easier and better they can be spatially arranged in the facade system. (...) The integrated facade is a vision that will materialise progressively throught the development of new components and technologies.

Amen.

Living walls & green facades

2010-08-19T20:35:00.002+02:00

Interesting article/blog on the matter. Part two coming soon:
http://sustainableppn.asla.org/2010/05/24/living-walls-confidential/
Follow it up!

Ideas for discussion

2010-08-19T19:06:00.003+02:00

I plan to deal with some of these issues in the coming posts of Facades Confidential:

Very very hot / cold: facade design in extreme weather conditions.
When is a facade a lightweight facade? Beyond load-bearing and non load-bearing walls.
GRC vs precast concrete cladding: pros and cons.
Continous walls vs framed facades: what we can learn from history.
The balloon frame and the early days of facade prefabrication.
Review of books about facades.
Review of articles about facades.
Procurement methods for facades and how they affect facade design and construction.
Common mistakes when installing stick system curtain walls.
The Equitable Building in Portland: the real starting point of the modern curtain wall.
Greek temples: how high priests robes and sandals led to a curved stylobate.
Facades, roofs or both? Limits of the building envelope concept.

More will be coming. I promise to provide some structure to it all, but later! Fun and good stories always come first.

Starting out

2010-08-18T17:29:00.016+02:00

Bridge Pavillion, Expo Zaragoza 2008. Zaha Hadid & Arup

The facade of a building is primarily a social, urban experience - even when it's part of a bridge! It is also an architectural concept, perhaps the most 'architectural' of the design tasks that are still exclusive to architects. The facade is the playing ground of the Vitruvian venustas, or beauty. A facade must be designed and built knowing its materials, support system, movements: it is also a tectonic element (the old firmitas). And finally, facades have a role as filters: air flow, heat and cold, sun radiation, daylight, noise etc go through it. This is linked with comfort and utilitas.

Nowadays, designing facades is a melting pot of related - or not so related - disciplines. No longer the exclusive domain of architects, facades are receiving more attention from engineers and urban planners. Facades are definitely an area for developing the future sustainable city.

This blog deals with facade design in the broadest sense. It is intended for architects, engineers, materials and systems suppliers, facade contractors, end users, students and academics alike. Perspective is critical: I am or have been part of any of these groups during twenty years of professional experience with facades. This should help with promoting opposed views and not avoiding clashes.

Let's see how far we can get ...