Did you always envisage the building as a steel construction?
Bryan Avery: We were always going to use a steel frame because we always knew we wanted to make it as fast as possible and as light as possible.
IMAX was finished in 18 months; our RADA building (AJ 03.05.01) took three years.
The concrete took six months, but it only took 12 months to get the rest in place. You can't do that in any other material.
How did you address the acoustics issues?
Bryan Avery: The other interesting thing about steel is the acoustics issue. It was a big problem here because we had to cope with noise both externally and from below - the Tube runs directly beneath.
We could not get a grasp on how much we should spend on acoustic insulation. If you ask anyone about it, they will say 'we want it to be perfectly quiet, ' but it's difficult to know what that means. We went to IMAX in Bradford and watched some films while recording our perceptions of external noise by pressing a button on an electronic counter - every time we felt the level of noise intruded on a film we pressed the button. By experimenting with different levels of noise, and taking into account different types of film and soundtrack we arrived at a level of attenuation which was acceptable to all parties, the point at which we stopped pressing the button and said 'that's it!'.
The outer glass wall is separated from the inner wall by a continuous circular gallery, so that it provides a buffer zone from the traffic noise. The inner wall is made of two skins of multi-layered plasterboard.
There are acoustic absorbents on some of the interior surfaces.
The external glazing and the auditorium are suspended from the steel frame to isolate them from vibrations of the road and the Tube. It is concrete at the base, and that's because underneath it we have the Waterloo and City line. But not all of the tunnels are cut and fill. Some of them are only 34m down, so we could not put any weight on them and had to span across. There are piles down to 20m, then the basement structure is concrete, with spring dampers on top.
The whole body of the building sits on these springs.
What the concrete did for me architecturally was to give a podium that forms a solid base and makes a wonderful walkway with the pergola above.
Now the vegetation has grown over it, it's quite a special space.
The external supports aren't actually supporting any weight at all. They're not supporting the weight of the wall, they're just there to stop the whole thing wandering about. That's how you get them to look so slim, in addition to taking a circle and banging it, so they're slightly ovoid.