Architecture: A touch of glass

large table dominates the offices of Bere Associates - a huge slab of glass supported on cast aluminium legs, connected by what looks like a sparkling glass backbone. The analogy is not accidental: Justin Bere had been working on the idea of a system of construction based on timber "vertebrae". To fulfil his philosophy of creating new systems using cheap, readily available components, mass-produced but using high- quality materials and craftsmanship, he was trying to find a supply of large wooden cotton reels. He spotted the glass equivalent masquerading as a candlestick in a friend's house. These big, chunky glass reels turned out to be isolators - a component in everyday use on top of electricity pylons used to carry high-voltage cables. Invented by Pilkington some years ago, manufacturing rights for the isolators had been sold to a French company but they were easy to obtain and well priced. Each is capable of supporting 18 tonnes, and when threaded on to a high-tensile stainless steel rod, they form an incredibly strong column which is slender, elegant and quietly dramatic.

A request from a client in Clapham, south London, to extend and bring more light into a north-facing kitchen on the raised ground floor at the back of a listed building provided the ideal opportunity for Bere Associates to put this new method into practice. Where many would have felt justified in adding a Victorian-style conservatory to this 1864 building, the owner, the architects and English Heritage ensured a more sensitive addition. The result is as discreet and flattering as a pair of modern rimless spectacles compared to the Dame Edna Everidge fly-away look that so-called period styles bring to the faces of unsuspecting buildings in the name of "authenticity".

On the raised ground floor overlooking the garden this glass room appears to be constructed with no visible means of support. The terms conservatory and extension fail to conjure up a space that is truly inside-out, bringing the living space into the open and inviting the garden in, but without the inconvenience of cold weather or the clutter of indoor plants.

The roof of frameless glass panels is supported on glass roof beams fixed to the house wall, resting on two glass columns. The design uses an existing brick wall on the west boundary, with the two new walls made from single sheets of toughened glass held by cast aluminium brackets threaded on to the steel between the isolators to hold the front wall, and used independently to form the corner and support the side wall. These brackets have two projecting outstretched arms with rocket- nose-shaped hands into which bolts are threaded from the outside through holes drilled in the glass. To allow for movement caused by temperature change nylon washers keep metal and glass separate, but the bolts are guided first through quirky, sunburst-shaped, cast- bronze washers which add a neat touch of craft and humour. A glass door fits almost invisibly into the side wall using discreet hinge fixings top and bottom. Small glass display shelves are bolted on through the glass at varying heights.

Fan convector grilles set along the walls keep it warm and free from excessive condensation and even the gutter is a long glass box which catches rainwater, directing it down a stainless steel rod to a circular bronze waterspout at ground level. Glass is a low-maintenance material that only requires washing with soap and water and so, with a modest twice-yearly window clean plus an annual hose down of the roof, this extension looks sparkling and pristine even in the polluted air of London.

At night the notion of invisibility is turned on its head as a clever lighting system, incorporated into the columns by means of stainless steel lighting rods, transfigures them into glittering illuminated sculptures and the room into a habitable piece of art. A purpose-built circular island unit in glass and aluminium has lights built into its central core, providing extra drama as well as an unexpectedly useful spot for keeping the vegetables warm during kitchen suppers. Blinds can be fitted for privacy or to avoid overheating in a south- or west-facing room. In this case, the aspect is north and east, and the owners prefer to moderate their kitchen behaviour rather than detract from the purity of the construction with blinds at night.

While the initial cost of construction was fairly high, it enhances the value of a listed building and has the enthusiastic approval of English Heritage. Wood and the increasingly ubiquitous UVPC are much more susceptible to deterioration than glass and in the long term, the cost compares favourably with that of the so-called "period" conservatories with their often over- detailed, expensive twiddles.

Bere Associates have now completed four more schemes based on the same principle as well as two restaurant facades, one at Pizza Express near the Barbican in the City of London.

Back at the office, the table with its skeletal base looks ready to walk off at any minute - but it wouldn't get very far, particularly as it took six people to carry the glass top up the three flights of stairs, a feat that Justin Bere is unwilling to repeat in reverse. Unfortunately, its current home being unsuitable for photography means that the table has had very little exposure - and consequently, no commissions. If you need a very swanky dining table or a splendid centrepiece for a boardroom, Bere Associates would be delighted to make one to your specification - and may be prepared to give a small discount in return for a photograph

Bere Associates, telephone 0171-837 9333