Substantial refurbishment of an existing office building to create a sustainable, high quality and beautifully designed workspace, in line with Great Portland Estate’s
net zero carbon commitment.

6-10 St Andrew Street is the substantial refurbishment of an existing office building to create a sustainable, high quality and beautifully designed workspace, in line with Great Portland Estate’s
net zero carbon commitment. Located within the City of London, the existing building, constructed in 1999, consists of an eight-storey reinforced concrete frame over a single storey basement.

The proposed design utilises the full potential of the existing building, limiting the amount of demolition required by maximising the floorplate efficiency. A new single storey extension will be added to the top floor, alongside a new pavilion structure at Level 09, and the creation of additional external terrace space at Level 08.

The design proposals maximise the reuse of the existing building, with 97% of the structure being retained, including the foundations. However, this required a lightweight solution to be found for all new structures. The proposed extensions have been designed in steelwork and composite metal slabs, which will be exposed to the underside, as these materials are lightweight whilst giving the aesthetic the architect wanted.

Alongside the embodied carbon stored within the retained structure, the design minimises embodied carbon by sourcing the steelwork elements from re-used stock instead of virgin steel elements. Using HTS’s internal Stockmatcher tool, 82% of the new steelwork required has been matched with suitable re-used elements, avoiding 24t of new virgin steelwork needing to be procured.

The HTS Stockmatcher gives a quick and considered solution to the current problem of how to best use reclaimed steel in buildings, maximising the efficient use of this low carbon material. The interface is simple, the inputs are flexible, and the results can be easily interrogated. HTS is looking forward to launching an open source version in June 2023.

Laura Batty, Associate – Technical Research & Sustainability, Heyne Tillett Steel