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working details

Rooftop conservatory, London Simon Conder Associates

A timber conservatory clad with polycarbonate sheet

The 5.3m x 4m conservatory consists of a white spruce timber frame, clad with 16mm triple-wall polycarbonate sheet, clear on three sides and translucent on the roof and the north-facing wall. The timber frame consists of 144 x 44mm timber posts secured by steel anchors to a timber upstand on the existing roof structure. The posts are connected with halved joints to 150 x 44mm roof joists which slope to a central box gutter. On the north and south sides the gutter extends beyond the conservatory wall and terminates in a downspout.

The polycarbonate sheets, used in standard 300 x 980mm size to minimize waste and cutting, are attached to 32 x 32mm horizontal battens using 3m clear vhb foamed acrylic adhesive, which allows a high degree of movement to take place between the two surfaces being bonded. The horizontal battens are fixed to the posts with a system of interlocking stainless steel clips which allow the battens to move freely in both horizontal and vertical planes relative to the fixed posts. Movement at this point is maximised by using vhb adhesive to bond the clips to both battens and posts. The vertical joints between the polycarbonate sheets are filled with Arbosil low modulus silicone sealant which also accommodates a high level of thermal expansion and contraction.

The posts are braced at the corners with Jacob Inox steel cables. The conservatory floor is made of 44 x 44mm timber decking laid on joists - of paired 150 x 10mm steel plates with 140mm x 20mm spacers between them - bolted to brackets fixed to the timber upstand which runs at the perimeter of the opening.

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