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Sticking point To create a rooftop conservatory within budget, Simon Conder developed a unique polycarbonate cladding system . PHOTOGRAPHS BY SIMON ARCHER

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working details

Simon Conder Associates has designed a rooftop conservatory for a loft apartment in a redundant nineteenth century warehouse close to Old Street, London. The client, a young couple in the computer industry, had bought a 1600ft2 (488m2) shell on the top floor; the purchase included the flat roof above it which was substantial enough to support a roof terrace. At first the client could only afford to fit out the shell space and, to give future access, cut a hole in the roof structure which was temporarily covered in plywood and polythene.

The conservatory is an integral part of the plan for the whole apartment; it gives access to the large 140m2 roof terrace and garden and directs natural light into the heart of the deep plan space below. It is a light airy space, 5 x 4m in plan, which brings the traditional benefits of a conservatory - linking garden to living space and modifying winter climate - to the apartment, but delivers them vertically rather than horizontally.

When the client decided to proceed with the conservatory their budget was only £15,000. It was clear that a conventionally glazed structure would be too expensive; instead the architect developed a solution based on a combination of lightweight polycarbonate sheeting and a braced softwood frame. The design had to accommodate the high levels (3mm per metre horizontally and vertically) of thermal movement of polycarbonate sheeting. Conventionally this degree of movement is accommodated by using proprietary gasket systems where the edges of the polycarbonate rest on a compressible rubber or epdm gasket which also stops water penetration at the joint. These systems are expensive and visually heavy. Instead the architect has developed a cladding system which allows the weatherproofing skin to move vertically and horizontally. The 16mm polycarbonate sheets are fixed to 32 x 32mm horizontal softwood battens with 3m clear vhb (very high bond) foamed acrylic adhesive. The battens are connected to vertical timber posts with a system of interlocking stainless steel clips. Low-modulus silicone sealant is used to seal vertical joints between the sheets.

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