• Client: Rhodes Trust
• Architect: Stanton Williams
• Photography: Hufton + Crow, Fisher Studios
• Completion: 2023
• Value: £38m
• Size: 4,465 m²
• Expertise: Structures, Civils

Rhodes House is a Grade II* listed building, built in the early 20th century, located in the heart of Oxford, occupied by the Rhodes Trust, an educational Charity. The demands on the building had changed over the years, with the Trust requiring more space with more modern and flexible layouts, but given the historic sensitivity of the city and building, expansion is challenging.

In collaboration with the Rhodes Trust and Stanton Williams, Webb Yates Engineers has delivered the integration of three new large extensions adjacent and underneath the existing building, as well as making sensitive alterations to the existing fabric, including new covered lightwells and opening up the lower ground floor by removing several walls and installing a new feature stone spiral staircase in the entrance Rotunda.

The new spaces house an open plan office, large multi-use auditorium, sunken residential courtyard with accommodation for events and a loadbearing glass pavilion floating in the landscape. Much of the new floor area was created below ground, with detailed analysis of the ground movements and groundwater flows to ensure the existing building would be unaffected by the excavations.

The walls and floors of the new double-height basements were formed from reinforced in-situ concrete with a high proportion of cement replacement, much of which has been left visible and expressed, reducing finishes. By utilising more efficient structural forms such as coffers, ribs and vaults, the amount of concrete used in the exposed slabs has also been greatly reduced by as much as 30%.

The two most eye-catching additions are also the most structurally challenging: the new structural stone stair and the glass garden pavilion. The post-tension, solid stone spiral staircase has been installed through the existing vaulted ground floor, providing access from the ground level to the new conference centre on the lower floors. Suspended within the existing arches by a compression ring, the staircase is held together by three tensioned steel cables. The 5m-high structural-glass pavilion in the West Garden, large enough to house 50 people, uses the giant panels of glass as the loadbearing walls. The pavilion’s green roof sits on a curved, structural timber lattice, which sits on all-glass walls with no structural supports.

The works to the existing required extensive investigations and surveys of the structure, as well as archive searches to understand the amendments to the building over the years. In particular, the connection to the new auditorium required transferring a three-storey bay window onto a new long-span concrete basement structure. To achieve this required sequencing the works closely with the contractor to install the permanent works early by utilising temporary steel stools that were cast in place through the supporting RC beam.

By understanding the building, the architectural proposals and the client’s requirements, the project has been phased to deliver the scheme while the building remained in use throughout. These extensive interventions to retrofit the century-old building were only possible by our team working closely with the full design team to develop a detailed and holistic structural scheme. The building is intended to facilitate the Rhodes Trust mission to expand its global programmes for many years to come, extending and expanding the building’s life into the future.