Jan. 9, 2015
The Broadgate Exchange House in London, celebrated for its simple yet ingenious structural system that unifies design and function in the mid-century Modernist tradition, was selected for the 2015 AIA Twenty-five Year Award. Designed by Skidmore, Owings, and Merrill (SOM) and completed in 1990, the Exchange House is a recognizable presence in central London. Its distinctive facades, defined by two parabolic arches against grids of windows, derive from SOM’s strategy to vault 10 stories of offices over the tracks that feed Liverpool Street Station. Far from droll, the grid and arch combine to improve extraordinary public spaces beyond. The arch on the Exchange House’s plaza size appears as an abstracted, amphitheater backdrop. The opposite arch, along narrow Primrose Street, soars upward and down again as you walk along, offering not just visual relief for office workers hustling to Old Spitalfields Market for a quick lunch. It encourages everyone to look up and see the building for what it is: a perfect marriage of form and function.
Recognizing architectural design of enduring significance, the Twenty-five Year Award is conferred on a building project that has stood the test of time by embodying architectural excellence for 25 to 35 years. Projects must demonstrate excellence in function, in the distinguished execution of its original program, and in the creative aspects of its statement by today’s standards. The award will be presented to SOM in May at the AIA National Convention in Atlanta.
Arc and cube
Broadgate Exchange House is a testament to Modern architecture’s ability to derive so much from just a few elements. This 10-story office building sits in the heart of London—one element of a massive master-plan completed in the 1990s. It’s a complex site with a complex history, but the Exchange House discerns all of it with two fundamental geometric elements: a cube and an arc. The project’s overall design aligns these two forms, holding up a multistory office building with arched bridge trusses in a way that exhibits each form’s elemental strength and integrity—efficient, rational, perfect.
From bottom to top, the Exchange House’s simple structural systems clearly communicate how the building works at a glance. It sits atop 18 rail tracks feeding into Liverpool Street Station, immediately to the southwest. Above this is a car parking lot, and the next level contains open space reaching out to a broad, terraced public plaza with green space and public art. The glass-walled curvilinear lobby is suspended from the first floor of office spaces, taking up only a fraction of this open area underneath the building. The Exchange House itself sits on eight piers, four on each side of the tracks, 260 feet across. From these piers spring four arches, two internal and two external. Utilizing air rights over the tracks, the bottom seven floors of the building are tied to the arches—a simple solution and as much a bridge as a building.
And, like a bridge, the Exchange House’s structural integrity depends upon its tectonic precision. In that way, it is architecture of the highest order.
A site’s reemergence
A Roman burial ground, a boggy intersection of ancient roads, old Bethlam Asylum’s burial ground—archaeologically, the area around Broadgate is rich in artefacts and bones. More recently, it was home to Broad Street Station on the North London Railway (NLR), which opened in 1865 and was, by 1898, the third busiest in the city. Broad Street Station was damaged during the First and Second World Wars and, over time, the London Underground’s growing popularity and greater London’s burgeoning bus lines, all but eclipsed the depot’s usefulness. By the early-1980s, as many NLR trains would skip Broad Street as would stop there, continuing on to the adjacent Liverpool Street Station, instead.
London officials shuttered the station in 1985. The same year, British Rail asked developers to submit proposals to redevelop the area and awarded the contract to Rosehaugh Stanhope Properties based on the strength of its Broadgate masterplan to create a new, mixed-use neighborhood that would become an information age hub of global capital. The 3.5 million-square-foot scheme included mixed-use offices, shops, restaurants, and landscaped public spaces, as well as a 35-story tower. Rosehaugh Stanhope hired SOM (whose offices occupy part of the tower) to bring the scheme along quickly and expertly. With legendary SOM partner Bruce Graham in charge of the project, London found a man used to dealing in extreme size—he had designed what was then the world’s tallest building, Chicago’s Sears Tower, as well as its John Hancock Center.
Completed in 1990, the Exchange House is an exceptionally self-assured composition. It’s a pure expression of minimalist structural honesty writ in steel and glass, and its contrast to some of the soft-spoken pink and grey granite Postmodernism in the rest of the Broadgate development reinforces this fact. The building reaches for, and attains, the enduring dream of Modernism: “It is impossible to describe the building’s architecture without describing its structure and vice versa,” reads the project’s submission portfolio. It is wholly the sum of its parts, each one visible and explicable.
The architects and engineers working with Graham at SOM reportedly chose the arcing truss system for three reasons: its efficient use of materials, its relative ease to build, and the formal dynamism and contrast it exhibits. Externally expressing the bridge trusses means that this building speaks beyond its site. Just a cursory look at the Exchange House makes it obvious that this building is a bridge, and the thin crusts of concrete below are decks over a fast-flowing stream of trains.
So much of design is the art of revealing contrasts—whether they are material, spatial, or formal. The Exchange House’s two geometric elements, the curvilinear arc and the rectilinear cube, are diametrically opposed. But, this opposition creates a system that sustains the building, which is an expression of the minimalist ethos of “less is more.” How few ideas can hold a building up? If you can get down to only two, like the Exchange House, they must be very strong ideas indeed.