Project Description

70 Gracechurch Street is situated on the site of the first Roman forum of the settlement of Londinium, in the heart of the modern-day City of London.
The development comprises a new 33-storey tower and a three-storey basement, containing office accommodation, retail, restaurants, and a public viewing terrace.
The scheme entails the adaptive reuse of the basement and large portions of the frame of the previous late 1990s Marks & Spencer building on the site, retaining around 60% of the original material by volume.

Project Challenges

The site presents several engineering challenges, primarily due to the presence of archaeologically significant Roman remains, which constrain site boundaries, and the existing piled foundations from two generations of previous buildings. The new development therefore requires transfer structures to move columns, avoiding clashes with the archaeology.

Adding 25 storeys to an existing eight-storey building poses a significant challenge in providing sufficient foundation capacity for the new structure while keeping the existing structures in place. By considering access and construction logistics from the start of design, we have designed a scheme that uses low-headroom large-diameter piling methods, and construction of a new raft within the existing basement volume, avoiding additional excavation.

Sustainable Methodologies and Outcomes

A major driver for the project is to achieve an ambitious up-front embodied carbon value for a tall office building. This has been achieved in structural design by our own estimation of quantities and embodied carbon from the start of concept design, ensuring the comparison of the embodied carbon impact of each design decision by the team. Key measures to meet sustainability targets have been the adaptive reuse of the existing basement and podium, the recovery and reuse of 120 tonnes of steel beams from demolished floors as columns in the new tower, and the efficient use of modest 7.5 and 9-metre spans for the new floor beams.