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The iconic, purpose-built US Embassy building, designed by Eero Saarinen, overlooks Grosvenor Square in Mayfair. Built in 1960, it is a fine example of contextual mid-century modernism and is Grade II listed. With the US Embassy moved to new premises, the building is being converted into a world class hotel with restaurants and commercial spaces. The design is based around the preservation and enhancement of the modernist design while responding to the ambitions and brief of the client to ensure the building’s long-term viability.

Reconfirming the building as part of Grosvenor Square Garden forms the basic premise of the design. The removal of all external security measures accrued over the years, as well as the original perimeter glacis, reinforces the connection of the building to its surroundings. Retail, restaurant and bar units are located on the ground floor and connect to a newly landscaped public realm, creating an active street front.

Internally, several additions and modifications had compromised the original design intentions. Central to enhancing Saarinen’s vision is the treatment of the first floor. All partitions, which were added to create separate office spaces, have been removed allowing a continuous reading of the exposed concrete diagrid ceiling – one of the building’s most unique features. The diagrid ceiling is restored and extended to create a grand, open piano nobile that reaffirms the original intention for the building to appear as a ‘palace on the park’. The restaurants and lobby lounge overlook the square while the rear section contains the reception and events spaces.

The upper floors are largely re-built behind the existing façade to house the guest rooms, distributed around a new central atrium. The basement contains the ballroom, spa and retail units as well as car parking and plant rooms. A vertically extended storey topped with a pavilion forms a new crown for the building. It follows the established language of the floors below with a new rhythm and increased floor-to-ceiling height. The design is the result of historical investigations which revealed an early Saarinen proposal suggesting a similar approach. The pavilion contains further guest rooms and additional public facilities that open on to terraces with views over Grosvenor Square to the east and towards Hyde Park to the west.

The Portland stone window surrounds of the historic façade have been restored and the envelope upgraded to achieve ambitious sustainability targets. In addition to the retained fabric on site, more than 4,000 individual elements have been carefully disassembled for cleaning and refurbishment before being reinstalled. The set-back penthouse floor is accentuated with gold anodised aluminium, a reference to the landmark gilded aluminium eagle sculpture by American artist Theodore Roszak, which has graced the building since its opening. This sculpture was fully restored and returned to the façade.