Concerning the article 'Growing planes' (AJ Focus, August 2004), which featured recent developments in Swiss green roof technology, readers may be interested in the enclosed photograph (above), taken in 1999.
This shows the offices of Swiss engineer and reinforced-concrete-shell designer Heinz Isler, built in 1964 near Burgdorf in Switzerland.
As can be seen, the building merges almost imperceptibly with the surrounding woodland, as the roof, which is an unprotected reinforced concrete slab, is covered in dense vegetation, including small trees. The unprotected green roof is possible due to the use of lightly pre-stressed, high-quality concrete for the roof slab, which is supported on a system of 'flexible' columns. These allow the slab to bend freely and sag in a very shallow catenary, thus maintaining the top surface in compression and uncracked. As the plants grow only in the detritus accumulated on the roof over the lifetime of the building, an automatic irrigation system maintains the water level on the roof in dry weather.
More information about the roof construction for this office and examples of the designers' innovative shells (most of which are also of unprotected reinforced concrete), can be found in my book, Heinz Isler, published by Thomas Telford in the series 'The Engineer's Contribution to Contemporary Architecture'.
John Chilton, Lincoln School of Architecture, University of Lincoln