Greenhouse effect - greenhouse and park at Terrasson Lavilledieu, Dordogne, France - Glass and Transparency

Architectural Review, The, May, 1998 by A. Uide

A pavilion in a park uses age-old masonry techniques and up-to-date glass technology, evoking myths of nature and history while providing sunny shelter.

The Dordogne is one of the most magical parts of France, still very rural and seemingly unspoiled, even if many of the old stone buildings are now country cottages for Dutch, English or German families. Despite the mechanization of agriculture, you can still find hosts of butterflies and orchids in the fields, and a profusion of ceps and truffles in the woods. A new five-hectare park at Terrasson Lavilledieu, designed by Kathryn Gustafson and Paysage-Land, has been set up to celebrate the qualities of the region's landscape and nature.

The principal building in the park is a greenhouse by Ian Ritchie Architects which grows out of the quite steep north-facing slope - literally so, for its battered curving north wall is made of local stone held in steel mesh cages (gabions), a form of construction used throughout the park by Gustafson and her colleagues to create retaining walls which define the terraces. The big wall bulges out of the hillside, seeming from a distance to be a ruined medieval bastion, but close up it is clearly of modern construction, with the random limy sandstone given a grand order by the geometry of the cages. And, on top, there is a delicate precise rim of glass strangely hovering.

From the uphill side, the glass flows out towards the valley, seemingly fiat (in fact a couple of degrees off horizontal). And from some angles, in certain lights (particularly when you first see it from a distance), it triumphantly fulfils the designers" intention of creating a 'virtual lake', related to pools elsewhere in the park, reflecting constant movements of clouds and trees. A real pool separates the glass surface from the path, and is intended to act as a deterrent to the daring (it is to be hoped that it will work, for although the experience of walking on glass is pretty scary, it could become part of the acceptance rituals of local youth).

The glass is supported on a white steel structure which is entirely independent of the curved stone wall. The steel cantilevers from a concrete structure cut into the slope. T-section ribs taper towards the outer (northern) edge where they are propped by a continuous tubular edge beam supported on cylindrical columns. Two layers of 8mm toughened glass separated by 3mm of polyvinyl butyral are supported from the ribs on stubby stainless-steel props, one in each corner of every sheet. These connect to the inner layer of glass only, leaving the outer one entirely plane and unsullied by obvious fixings, so permitting (from oblique angles) the virtual lake illusion. The fixing heads are mounted on spherical bearings, close to the glass, so minimizing local bending stresses in the glass caused by tolerance differences and differential expansion of glass and steel. The system is somewhat similar to the one Ritchie used in the Leipzig exhibition hall (AR March 1996 p77), but there the spherical bearing (in effect a three-dimensional pin joint) is in the plane of the glass itself.

The super-sophisticated glass plane oversails the edge of the rough stone wall. There is no connection between them, for the internal climate is supposed to be a modified version of the external one, and air can of course filter through the gabions as well as the slot between glass and stone.

The greenhouse is intended to have a multitude of uses. Its curve is caused by a little auditorium which can be used for theatre, conferences and exhibitions. This generous and cheerfully luminous volume is overlooked by a little cafe, a shop and a study area cut into the hill under the long pool which separates glass from path above. Citrus trees have been planted inside the curve of the stone wall. They are sprayed and watered in the summer, and the evaporation from them (and the rubble behind) is expected to temper the heat of the sun shining through the glass roof (provision has also been made for blinds between the ribs to mitigate the effects of summer's hottest days). The wall itself is of course a thermal flywheel, which is expected to be particularly effective in winter, when the greenhouse effect will enhance the sun's heat in the space and the wall will capture some of that heat, slowly emitting it when the air temperature falls.

Only experience will tell how the calm little place will work. But, as a building, it is already astonishing in its mixture of rough and smooth, ancient and modern archetypes, transparency, opacity and reflection.

Architect

Ian Ritchie Architects, London

Project Team

Simon Conolly, Edmund Wan

Landscape architect

Paysage-Land/Kathryn Gustafson

Engineers

Ove Arup & Partners: John Thornton

Site engineer

ARC Ingenerie, Brive