Rainscreen of weathering steel panels
The new four-storey extension to the theatre, containing offices and dressing rooms, is clad with a rainscreen of solid and perforated weathering steel (Cor-Ten) panels. They are sized to reflect storey heights and spandrel areas and are fixed, except in front of window openings where they are formed into sliding and hinged screens.
The 150mm thick cast in situ concrete structure was waterproofed with a liquid bituminous membrane and fitted with a series of stainless steel support and restraint brackets, which were lined and levelled.Mineral-fibre insulation bats, 75mm thick, were then pinned to the structure; they are lined on the outside with black glass-fibre tissue to assist in shedding water and to give a neutral background to the perforated screens.
The oak windows were sealed to the waterproofing and a second series of stainless steel support and restraint brackets was fixed to the first, with a thermal resistor between them.
Each 5mm thick perforated Cor-Ten panel is fixed through the unperforated perimeter zone to a bracket with a stainless steel button-head socket screw. To ensure that the stainless steel and Cor-Ten are totally separate, the screw is sleeved in nylon spacers and washers; the spacer is thick enough to avoid rainwater bridging from Cor-Ten to stainless steel and vice versa by surface tension. Stainless steel captive nut clips were fitted over the top of each bracket to enable the button-head socket screws to be tightened from the outside.
Cor-Ten earthing connector tabs are used to achieve electrical continuity between panels.
At first-floor spandrel level, a stainless steel gutter is set below the rainscreen to collect the runoff. The ground floor is clad with red-painted solid profiled panels of Cor-Ten, fixed in the same way as the upper panels.