Behind the distinctive concrete façade of the former government offices lies a 170m by 70m, repetitive, entirely steel framed structure enclosing five inner courtyards.
Internal design is simple and solid, based on a 3.2m or 3.8m grid of 177mm by 228mm steel I-section columns.
As they were originally built to withstand heavy storage racks filled with state pension records, there has been no need for further reinforcement in the upper floors.
'There was no need to change the foundations either. The change of use from storage to residential plus the new penthouse floor is about equal to the old storage loading' says Cameron Taylor Bedford principal engineer, Daniel Claydon.
An added penthouse level has necessitated a new roof to keep loadings on the original roof down.
The ground floor slab is the only structural element to be replaced. 'We would have had to break the slab up anyway to make room for all the new drainage installations, ' explains Claydon.
Close to the main building, the original boiler house, chimney and the former magistrate's court will be knocked down to make space for a single storey basement 400-space car park.
Thermal ficiency of the external walls is to be improved by blasting blown fibre cavity insulation (Rockwool) through drilled holes under pressure.
Internal blocks will be dry lined 'so overall wall build up is improved', explains Clayton.