Working details: A WAVED STEEL ROOF WITH PROJECTING EAVES
The new 12,000m2 building has a steel structure of I-section columns supporting a series of 535 x 210mm universal beams as rafters which arch in a sinusoidal wave between columns. The rafters are braced by 535mm- deep Cellform beams at valleys and at the perimeter. The ridge of the wave allows light to penetrate deep into the building through a continuous strip of frameless clerestory glazing at the eaves; it forms natural gutters in the valleys for water run-off, doing away with the need for added falls.
The rafters support a diaphragm roof formed of a deep profiled structural steel deck. It is reinforced and trimmed at the rooflights and cantilevered over projecting rafters at the eaves. The deck is covered with a vapour barrier, 85mm dense mineral-wool insulation and a Sarna single-ply membrane. The curved rafters are 7.5m high at their lowest point. This allows a mezzanine floor to be placed along the northern edge.
The walls are clad with a combination of structural silicone-glazed aluminium curtainwalling and sinusoidal profiled steel cladding with a silver pvf2 finish. The curtainwall is a Stoakes system modified by the architect; the double-glazed units have a factory-bonded edge bead by which they are mechanically fixed to the aluminium sub-frame. An extruded aluminium channel and silicone gasket form a watertight recessed joint between the panels.
The horizontally profiled metal cladding is supported by vertical cladding rails fixed back to structural steel liner trays. The trays are fixed to the main structure and to intermediate wind-posts, and are infilled with insulation batts. The vertical junction between the profiled-steel cladding bays has a purpose-designed top-hat section of extruded aluminium which 'sandwiches' the end of the profiled steel, avoiding clumsy lap joints.