The four-storey foyer block built on to the west side of the Grade II-listed Victorian theatre, and containing bars, circulation, wcs and offices, is separated from the original theatre by an atrium - a four- storey-height space, covered by a translucent barrel-vaulted roof. The Victorian brick wall of the theatre now forms one side of the atrium, reflecting the original street pattern. Bridges at first- and second-floor level cross the atrium to link the foyer to the theatre.
A continuously glazed rooflight is set at the perimeter of the roof. It rests on a 305 x 89mm rsc fixed to the top of the brick wall. The pitched roof was re-slated and raised at the eaves, and a new gutter and syphonic drainage system inserted to drain the rooflight, overlaid with a walkway to give access for maintenance.
The barrel-vault roof is made of Kalwall, a translucent structural composite consisting of an aluminium I-beam grid system bonded to grp-face sheets. It was chosen to give an even quality of light without visible structural support. The Kalwall self-supporting curved panels interlock at the apex with a concealed gusset strap, and spring from a pair of trusses which runs the length of the building, resting on 168mm-diameter chs columns at 11m centres. Each truss consists of a bottom chord, a 457 x 191mm universal beam, connected by solid 100mm-diameter posts to a top chord, a 254 x 254mm universal column. The webs of the top chords run horizontally to take the lateral thrust of the Kallwall roof and act as a gutter. Opening smoke/heat vents fill the space between the top and bottom chords.
The gable of the barrel vault is glazed, with a flat roof alongside acting as a walkway for cleaning and maintenance.