The inaugural winner of the CTBUH 10 Year award, 30 St Mary Axe (The Gherkin), helped to define a modern, open, and progressive image for one of the world’s oldest financial centers and set a benchmark in architectural quality for a new generation of tall buildings. The Gherkin has also been extraordinarily embraced by the public. In 2012, 3,000 people attended the Open City event to look inside, some queuing from 2am, with twice that number turned away. As well as appearing on a first-class stamp, the tower has been used extensively in the promotion of London through advertising, notably as the symbol of London on Olympic bid posters. The building is not only a cultural success, but a commercial one, consistently commanding higher rents than its peers in the City. Thus, the Gherkin more than satisfies the conditions for “contribution to culture / iconography.”

Under the engineering performance heading, the building’s tapering form and diagonal bracing structure have afforded numerous benefits that continue today: programmatic flexibility, naturally ventilated internal social spaces, and ample, protected public space at the ground level. The Gherkin has performed exceptionally well in high winds – its robust aerodynamic form counteracts the movement that would otherwise be felt in a building of its height. Environmentally, this form, which slims toward the base and the apex, creates external pressure differentials that are exploited to drive a system of natural ventilation during the summer months, and enabled the creation of a generous, comfortable plaza at street level, protected from high winds by the tower’s form.

The Gherkin’s accommodating structure has had follow-on benefits in the internal environment and occupant satisfaction category. Column-free floor plates, and a fully glazed façade open the building to light and views. Atria between the radiating fingers of each floor link vertically to form a series of informal break-out spaces that spiral up the building. As the occupancy has shifted from sole tenant to more than 14 firms, these “green lungs” have continued to provide valuable internal social space within the dense medieval street pattern of London. Six radial fingers of accommodation on each floor, with light wells between, combine the benefits of both curvilinear and rectilinear configurations, maximizing the proportion of naturally lit office space.

The geometry of the tower demanded an innovative system for the fabrication of individual cladding panels, due to the high level of variation. The 3D computer model of the system was linked directly to the production line, with major implications for the subsequent construction of complex buildings around the world.

The design placed a high priority on flexibility. Every possible configuration within the building, from cellular offices to entirely open plan floors, persists today. The widening and slimming profile generates a variety of floor plates that can respond to different sectors and markets.

The building is exemplary in terms of environmental and energy performance. The natural ventilation system operates by importing external air into the building through building management system (BMS)-controlled, motorized perimeter windows placed in each of the six lightwells. The adoption of natural ventilation varies, depending on tenant layout and requirements. Approximately 50 percent of occupants currently use the system.

An active, ventilated facade is used across the whole building. This comprises a low-emissivity, double-glazed clear external unit to the outside and a single-pane interior glass, separated by a ventilated cavity. Within the cavity are solar control blinds operated by the BMS. A proportion of office extract air is passed through the facade cavity, which takes the intercepted heat reflected by the blinds from the facade back to the outside via on-floor air handling units. This minimizes solar gain in the offices and makes the façade effectively part of the office extract system.

The pitch angle of the blinds is fixed by individual, BMS-controlled dedicated motors to an optimum position to reduce solar gain within the office spaces at all times, while maximizing light transmission through the gaps in the blinds. Ten years on, this system is operational and effective in providing user comfort, while reducing energy demand.

The Gherkin is not just an icon; it also provides a contribution to the urban realm beyond itself.
The outdoor space is another great success of the project, where the building’s contribution to the city has been most evident: the plaza is full of people in the summer, with food markets, city events and a dynamic arts program illustrating its success.