The project involves adding an extra two floors to the eight-storey building, called Walsingham House.
Walsingham House is in a conservation area, opposite the Grade I listed St Olave’s Church, and adjoins a four-star hotel. Given the history of the area, the first stage is an archaeological investigation to uncover and record remains, which are expected to include sections of a Roman road and structural elements from the 13th, 16th and 17th centuries.
The transformation and upgrade of Walsingham House will see ISG take apart the interior structure of the building, while retaining the Portland stone façade.
New piled foundations will enable the construction of a steel frame structure, adding two floors and creating nearly 50% more internal office space to provide a net internal area (or NIA) of 65,000 sq ft.
Externally, the retained façade will be cleaned and restored. To achieve a targeted BREEAM Excellent rating, ISG will upgrade glazing with high performance units sympathetic to the original art deco window designs. The two additional floors will feature curtain walling and contemporary Portland stone cladding sympathetic to the original façade.
Upper floors will be served by a single core featuring three lifts and two staircases. At basement level, ISG will install a new substation.
The open plan office layout will be fitted out to a high Cat A standard, with a spacious reception area created at ground floor level.
Matt Blowers, managing director of ISG’s UK Fit Out and UK Construction South business, said: “Current schemes at nearby Dixon House, Alderman’s House and 20 Old Bailey, continue to demonstrate our capability in these highly technically façade retention projects. As prime office locations continue to attract high rental yields, property owners are increasingly looking at all options to increase capacity and provide modern layouts to maximise portfolio yields.
“Managing complex interfaces and operating in logistically challenging and busy environments is where ISG really excels as a business and this latest scheme further strengthens our credentials as London’s leading office contractor.”
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