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Embassy of the United States of America, London
24 Grosvenor Square, London, UK
associated engineer
Felix Samuely
Frank Newby
FJ Samuely & Partners
date  1957 - 1962
era  Modern  |  category  Building  |  reference  TQ281808
The Grade II listed American Embassy in London's Grosvenor Square was Britain's first purpose-built embassy building. Well known to Londoners for the massive security structures added in 2008 that now dominate the square — which has a long association with the USA — the building itself is very interesting, with its exposed concrete diagrid.
In 1955, the Americans held a limited competition for the design of the embassy. Eight architects took part, and the design of Finnish-American architect Eero Saarinen (1910-61) was selected. British practice Yorke Rosenberg & Mardell was appointed associate architect for the construction.
FJ Samuely & Partners, led by principal Felix Samuely (1902-59) and fellow partner Frank Newby (1926-2001), were engaged as structural engineers. It seems Newby won the appointment for the practice on a trip to the USA during which he met Saarinen.
The embassy (actually a chancery, as the ambassador lives elsewhere) occupies the full block at the western end of Grosvenor Square, its symmetrical appearance reinforced by the centrally located huge gilded bald eagle on its 85m frontage. The land belongs to Grosvenor Estates (in the UK, land ownership is often separate from building ownership or leasehold), making the project unusual as most US embassies are on American-owned sites.
Architecturally controversial when it opened in 1960, the building has come to be better appreciated in recent times for its articulated facades and lively design. Saarinen was a leading architect of the 20th century, known for moving Modernism on from strict adherence to its tenet that form should follow function. He died in September 1961, soon after the completion of this building, his only British project.
Construction began in 1957. The embassy is U-shaped in plan and provides nine floors of accommodation — three basement and six above-ground levels, with the upper level a set-back 'attic'. The ground floor features a raised ceiling, which is expressed in the elevations by a different facade treatment.
The building is founded on mass concrete strip footings and reinforced concrete ground beams, some of which are formed as part of the ground slab. The basement levels are a combination of precast and in situ reinforced concrete columns, slabs and panels.
The design makes use of the construction form known as a diagrid (diagonal grid), which was developed in the 1920s, though more often seen in steel structures. Here it is used in concrete — each above-ground level consists of a diagrid composed of metre-deep intersecting beams supported on cast concrete cruciform columns. The first level cantilevers from the ground floor wall line, increasing the virtual footprint of the building.
The floors of levels two to five were constructed using Samuely's trademark combination of precast concrete soffits and troughs (supported on the diagrids) with in situ concrete above. In this technique, the precast elements are used as permanent formwork for the pouring of the slabs. The use of precast elements reflects the advances in concrete technology at the time.
The walls of the building are loadbearing, composed of precast concrete panels. Gilded aluminium frame windows, tall at ground level, smaller higher up, punctuate the facades. The main facade is 22 bays long, with a central five-bay entrance section — although the public entrance is now elsewhere. The concrete panels are faced in Portland stone for which a system of invisible jointing was developed. The north and south facades are 13 bays long.
The competition brief called for the design to respond the Georgian scale and character of Grosvenor Square. Saarinen's response has been chacterised as a modern interpretation of a classical temple, complete with Portland stone-clad plinth. The rhythm and form of the facades goes a long way to soften the impact of a large building mass.
The use of the diagrid as a motif has been carried through into the building's details, and is a principal feature of the design. However, the intersection of the diagrid with the rectangular set-out of the columns and facades was awkward and necessitated highly complicated junctions. A series of isometric drawings was made by engineer Tony Hunt (b.1932), who was working at FJ Samuely & Partners at the time. They were designed to help the contractor with positioning and the installation sequence of the precast elements. "A Chinese puzzle" was Hunt's description.
An America, Saarinen often worked with Norwegian-born engineer Fred Severud (1899-1990), including on the Yale Art Gallery project that was the embassy's antecedent. Severud said that, "Real engineering is like a melody, softly played in tune. Engineers are prone to juggle figures rather than ideas ... ". This opinion was shared by Newby, who took over as senior partner at FJ Samuely & Partners after Samuely's death in 1959. Newby thought that structure should not dictate to, or overwhelm, architecture.
The embassy building is due to be vacated by the USA some time after 2017, when its new chancery will be completed at Nine Elms in south London.
Architect: Eero Saarinen, Eero Saarinen & Associates
Partner in charge: J. Lacy
Associate architect (UK): Yorke Rosenberg & Mardell
Mechanical engineer: AF Meyers & Partners
Research: ND
"Architect and Engineer, A Study in Sibling Rivalry" by Andrew Saint, Yale University Press, Newhaven and London, 2007
"Felix Samuely — Teacher, Innovator, Engineer", student thesis by Gregory Hardie, University of Cambridge, IDBE 8, March, 2005
"US Embassy, Grosvenor Square, London", Architectural Design Magazine July 1960 pp 270-275
"Proceedings of the First International Congress on Construction History, Madrid 20th-24th January 2003: ‘The Work and Influence of Felix Samuely in Britain’" by David Yeomans

Embassy of the United States of America, London