8 November 2010

Central Saint Giles: Piano goes to London

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.


Mic said...

Thanks for this. Great stuff, Ignacio. Mic

Andrew said...

Interesting article but is the cladding used fire-resistant? I have in mind the Grenfell Tower cladding disaster.

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