The South Molton Triangle is a new redevelopment proposal to transform a prime, but underutilised, Mayfair area into a high-end office, retail and leisure community. The ambitious brief was to develop an exemplary project championing low embodied carbon and circular economy principles. The scheme centres around the re-use of listed buildings and includes two new office buildings carefully set behind existing façades.

The site covers two acres within the Mayfair Conservation Area. Located adjacent to Oxford Street and Bond Street, the site currently acts as a gateway into Mayfair from the north. The new Elizabeth Line at Bond Street will create an additional arrival point and deliver a huge number of additional visitors to the area.

The planning application, prepared by Hopkins Architects and approved in 2021, builds on the existing heritage of the site with a truly mixed-use proposal including office accommodation, leisure space, housing, a boutique hotel opportunity and a high-quality public realm offer animated with new ground floor retail and restaurants.

Grosvenor and Mitsui Fudosan UK, under a joint venture agreement, have approved the commencement of the two new office buildings at the heart of this scheme. Designed by Hopkins Architects, they will provide approximately 180,000 sq. ft. of prime office space combined with 60,000 sq. ft. of new shops, restaurants and cafés. The new office buildings have been designed for maximum leasing flexibility, with highly adaptable large office floor plates. The upper floors all benefit from connections to external landscaped terraces, with larger terraces provided on the roof for the use of all occupiers. Both buildings have a mixed-mode ventilation strategy, with openable windows to all floors. These features, together with highly efficient air source heat pumps and on-floor heat recovery, have contributed to the buildings meeting the highest environmental standards including BREEAM Outstanding and WELL Platinum standards.

The client set an ambitious embodied carbon target of 500kgCO₂e/ m², which has pushed the design team to continuously review and research options for minimising embodied carbon. This has included the specification and procurement of low carbon steel for the building frame, the re-use of existing onsite material, and the careful choice of new materials.

Hopkins' highly strategic approach has been to balance modern office requirements for large floor plates with the preservation of heritage assets and energy performance. A fabric-first approach to both the existing and new façades has been a key design driver in minimising the building in-use energy demand. The existing façades are all upgraded with spray-applied ‘breathable’ thermal insulation which results in a 7-fold reduction in heat loss through the wall, whilst minimising the risk of detrimental damage to the existing fabric.

In line with Grosvenor’s Circularity Toolkit, a pre-demolition audit of the existing building was carried out which highlighted material potential and quantities. Hopkins then reviewed the materials available and specified brickwork from the existing building to be used to form the internal basement walls, and salvaged ceiling and carpet tiles to the back of house areas.

The facades of Brookfield House and 56 Davies Street needed to be dismantled for site logistics and to make adjustments to the window locations. Stone specialists PAYE helped to develop a strategy to dismantle the Portland stone façades retaining as much of the original material as possible. 90% of the stone from both buildings will be reused in the re-built façades. To meet the shortfall and provide additional material for the new element of façades, a strategy has been developed to split the existing stone in half. This maximises the material yield and offers both circular economy and heritage gains - the new stone matches the existing stone - while lowering the embodied carbon when compared with specifying new stone.

The construction of the two office buildings is scheduled to complete in 2027, following other key elements of the South Molton Triangle masterplan: the restoration of the Georgian properties on South Molton Street and the boutique hotel at 40-46 Brook Street.