The steel frame of the new buildings is largely an orthodox structure centred on a 12 m x 12 m grid. Steelwork was procured via an XSTEEL 3D computer model issued electronically at tender. This was believed to be the largest steelwork project tendered in this way. The individual elements of the cladding, mainly stone-faced precast panels, were stacked and supported vertically at ground floor only. Due to ground constraints, mainly archaeological, several support points could not have foundations.
This was overcome by turning a number of the steel facade frames into four-storey vierendeel girders, allowing the pre-cast units to be supported from hanging columns laterally restrained at the base.
The west building provides public access to a Roman wall and Medieval bastion, one of the Scheduled Ancient Monuments on the site. To increase headroom in the chamber, the lid was removed, the walls extended and the lid replaced. For protection, the structures were wrapped in foam sheet protected by ply on top, and filling the chamber with washed sand which was vacuumed out on completion.
The structure of the glass atrium roofs is minimalist. The office atrium roof is supported on 6m glass beams with two failsafe devices in case of glass fracture - each beam is laminated with two sheets of glass, with each leaf capable of taking the full design load. In the event of both sheets breaking, a catenary wire comes into play to prevent collapse.