51 Lime Street acknowledges that the way in which an office building responds to the context and spirit of the city in which it stands is as fundamental to its success as the acknowledged benefits of natural ventilation, light, open space and a view. As a result, the architects continue their built explorations into new strategies for flexible, column-free office space, but have also created the idea of the “urban room”, where genuine connections to the public realm are established, and the way in which the building “touches” the ground is paramount.

51 Lime Street, also called the Willis Building (after its primary tenant), sits in the heart of the City of London. It lies to the east of Richard Rogers’ 1986 Lloyds Building and responds to this unique location with an elegant concave form. The project is significant in both urban and environmental terms—51 Lime Street is among a number of projects in the City of London that have struck a delicate balance between commercial requirements, the need for flexibility, and respect for the area’s world-famous architectural heritage. The original building for Willis Faber Dumas by Foster + Partners in 1976 was a seminal project for the practice, an open office building characterized by its sense of community —this spirit has been kept alive in the new UK headquarters in London, with expansive roof terraces that offer broad views over the city.

The development comprises two separate buildings which step down to a new public plaza. The building at 1 Fenchurch Street responds to the smaller scale of Billiter Street and Fenchurch Avenue, while the Willis headquarters building rises to the west of the site. The smaller building’s concave façade encircles the plaza and its curved corners maintain important view corridors, and also restore a pedestrian route through the site, reinforcing the medieval street pattern. The landscaping also features sculpture reclaimed from the previous building, linear benches and a living wall to replace the existing ‘party wall’ between the Willis Building and its neighbors, improving the view from the building and encouraging biodiversity. With a fringe of cafes, restaurants, shops and bars at the tower’s base, 51 Lime Street extends the vibrancy of the nearby Leadenhall Market, a particularly lively shopping area in the City with a strong architectural character.

As towers grow ever taller, the strategies to achieve stability are increasingly central to the design approach. On plan, the Willis headquarters has been developed as a series of overlapping curved shells, while its section is arranged in three steps. The roof terraces overlooking the plaza on the lower two steps are directly accessible from the office spaces. Both buildings have a central core to provide open floor plates and maximum flexibility in use, so they are able to accommodate a number of different configurations for one or more tenants.

The entire development is visually unified by its highly reflective façade. The pressed form of the panels and their mica finish give them depth and texture. A strong language is established through the interplay of solid and glazed panels arranged in a saw-tooth pattern. The fins also increase insulation while reducing glare and solar gain—just one of the strategies that have contributed to the building’s BREEAM “excellent” rating. Together with highly efficient services equipment and systems and extensive bicycle parking, the building’s progressive environmental strategy surpasses statutory carbon reduction targets by more than 20%.