Set in the St James’s Conservation area, this project involves the redevelopment of an office building on a tight site with street frontage on three sides to St James’s Square and Pall Mall.
The existing building has been demolished and replaced with a new seven-storey office development. The existing mix of brick and stone façades have been retained and extended.
The new structure has piled foundations due to the unfavourable ground conditions of 4m of made ground underlain by alluvium. In order not to add extra vertical loads onto the existing perimeter foundations supporting the façades, the new structure has vertically slotted holes so that only horizontal restraint to the walls is provided.
The superstructure is a hybrid of steel framing for the main floors and in-situ reinforced concrete for the core walls and slabs. The floor footprints are relatively small, but we increased the floor space for office rental by switching the steel frame core to in-situ concrete by using thinner wall construction. Shallow floor beams and floor slabs set within the depth of the beams enable more generous floor to ceiling heights.
As the site location is close to the Crossrail 2 corridor, engagement with Crossrail representatives was necessary from the early stages of the design process to satisfy them that the new piling did not encroach upon proposed tunnel route and exclusion zones.
We also worked with the contractor during these early stages to develop steel-to-concrete connections which would allow the steel frame to be erected at the same time as the concrete core, ultimately resulting in a shorter and more efficient construction programme.
Currently on site.