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Laminated glass roof plays a central role in greenhouse light, solar warming, and visual unity with environment

The Terrasson Greenhouse, a research center and public performance space situation on a peaceful hilltop in the Bordeaux region of southwest France, won a Special Merit mention for Simon Conolly of Ian Ritchie Architects, London in the 1997 DuPont Benedictus Awards.

Greenhouse roof: vast, sprawling laminated glass resembles a pool of water and light

Originally conceived as a reference library and a research center on plants, as well as a public performance space for theater, conferences, exhibitions and other municipal events, the Greenhouse also serves as a peaceful, sheltered space and a tea house in a five-hectare park designed by landscape artist Kathryn Gustafson.

The greenhouse has a clear, flat roof of laminated glass which reflects, like a lake, the changing sky and the foliage of surrounding trees. Reminiscent of the Victorian crystal botanical gardens, the Terrasson Greenhouse recalls the importance of greenhouses in the development of the European garden.

Greenhouse glass roof allows full vision of sky

Laminated glass roof

The laminated glass roof plays a central role in the greenhouse, not only opening up the structure to light and solar warming, but also visually uniting structure and environment. This is enhanced by a surface that is not interrupted by fixings, but rather is assembled into the inner sheet of toughened laminated glass only and is covered by continuous outer sheets.

The flat glass roof presents a sheer and unbroken, reflective surface to the viewer, especially from above or from a distance. It appears to be a 'virtual lake', relating to the water features elsewhere in the landscape design. Mirroring the form of the amphitheater in the hill alongside, the roof also gives a reflected view of the sky, the landscape and the upper part of the town of Terrasson.

Design issues

The glass roof is made from two layers of 8mm toughened glass, bonded with a 3mm PVB interlayer. The thickness of the interlayer is required to accommodate a flange on the head of point fixings, which penetrate the inner layer of glass only, leaving a sheer and unbroken reflective surface to the exterior. The fixing head is articulated on a spherical bearing, close to the plane of the glass. This allows the fixing to rotate with any relative deflections between glass and supporting steelwork and minimize the transfer of any additional bending stresses into the glass. The origin of this fixing was in the 'phantom fixing' developed by Ian Ritchie Architects in 1987 for the spherical glass 'Pearl of the Gulf' in Dubai.

The 1997 DuPont Benedictus Judges said: "Glass is interesting for a garden … from the top, a circular shape, it is like a pool of water … There is a perception of 'play with the landscape', very fresh … Nothing is forced; it is interesting, elegant …"