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

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

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

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

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

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...