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A glazed facade with LVL mullions

The Idea Store, containing a library, cafe, spaces for adult education and computer access, is a single-storey, lightweight steel structure, approximately 60m long, built on the roof of a 1960s concrete flat-roofed shopping arcade. At the south end it extends beyond the original building to create a double-height atrium - the main entrance - with access at ground-floor level.

Set behind a parapet upstand, the gently sloping roof consists of an insulated single-ply membrane on a structural deck - a double layer of 15mm spruce ply supported by 300 x 60mm laminated veneer lumber (LVL) joists at 360mm centres. The joists span between a grid of 300 x 200mm RHS roof beams and are exposed to form the ceiling.

The walls are glazed from floor to ceiling with doubleglazed units. The working detail shows two alternative glazing conditions. In the double-height atrium (far right), some units are glazed with clear glass and others are translucent, with a tinted PVB layer in the laminated pane.

Pivoting vents at the back of the upstand and at the base, together with automatically operated sensor-controlled blinds, act as a ventilation chimney to extract heat from the atrium.

The east wall (right) has firerated insulated steel panels fixed behind the glazing to act as a solar screen and to form the backs of shelves.

The edges of the doubleglazed units are silicone-jointed and mechanically fixed to a 60 x 60mm box-section aluminium frame with toggle fixings. The aluminium frame, in turn, is laterally supported by a series of 60mm wide and 300mm deep LVL mullions that run from floor to ceiling, supported by concealed brackets. The mullions in the atrium are stiffened with 15mm steel-plate inserts.

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