The Gherkin's curved glass skin contains just one curved pane
London's rounded tower at 30 St Mary Axe looks like a single sweep of curved glass. In fact every pane is flat except the lens-shaped cap at the very top. The building breathes through spiral shafts, uses about half the energy of a typical tower, and stands on the site of an IRA bombing.
The site once held the Baltic Exchange, the marketplace for shipping contracts, and the Chamber of Shipping. A Provisional IRA bomb on 10 April 1992 badly damaged both. Heritage officials first insisted the old façade be restored, then found the damage too severe. The salvaged Exchange interior and frontage were sold for £800,000 and shipped to Tallinn in Estonia to await reconstruction. A plan for a 386-metre Millennium Tower was dropped as wildly out of scale and a risk to airport flight paths, and in August 2000 Deputy Prime Minister John Prescott approved a smaller scheme.
Foster and Partners won the design in 1999, with Arup as structural engineers and Skanska building from 2001. The tower rose 41 floors to 180 metres, was finished at the end of 2003, then opened its doors on 28 April 2004 as the UK head office of Swiss Re. Its tapering form keeps it modest at street level, so passers-by barely notice it until they are beneath it. A diagonal grid around the outside makes it stiff enough to resist wind without extra bracing.
Gaps in every floor form six spiralling shafts that ventilate the building naturally, drawing warm air out in summer and trapping solar heat in winter, while letting daylight deep inside. Tenants spoiled some of that by adding glass partitions for security. Because a bar was planned for the 40th floor, the lift machinery could not go on the roof, so the main lifts stop at the 34th and a second lift climbs from below. In 2005 one of its panels fell to the plaza, prompting checks on the other 744.
The tower won the 2004 Stirling Prize, the first time the judges were unanimous, and was later voted the world's most admired new building. It sold in 2007 for £630 million, then a British record for offices, and again in 2014 for £700 million to the Safra Group. During construction, workers found the skeleton of a teenage girl about 1,600 years old; she was reburied on the site in 2006.
Source: The Gherkin
