The £10.5m project will see two existing six storey buildings with non-aligned front elevations consolidated into mixed-use property.
ISG will remove the two façades and extend the stepped back structure to allow the installation of a single curtain walling system.
To increase overall floor space, ISG will also demolish the sixth floor and build a steel frame and glazed structure that extends across the entire footprint of the building.
Targeting a Very Good BREEAM environmental performance rating, Summit House will feature a green sedum roof, modern building management controls and a combined heat and power system.
ISG’s Stuart Deverill, managing director – London, said: “ISG has again proved successful securing a complex office rationalisation project requiring extensive temporary works and undertaken in a busy central location.
“This project closely follows our appointment on the City Tower scheme in Basinghall Street and our successful completion of the challenging £40m No.1 Kingsway project in the West End, clearly demonstrating our pedigree and credentials in the commercial office sector.”