The new Sixth Form Annexe (now known as The Walters Building) is tucked behind a Grade II Bath stone ashlar faced Georgian Listed building, in the historic area of Clifton, in Bristol.
Project Name: The Walters Building
Studio Name: O’LearyGoss Architects Ltd
Structural engineers: KB2
Main contractor: 21st Century Building Services
Stonemason: Rowland Stone Ltd.
Client: Clifton High School
From the earliest design stages we wanted to use an ashlar Bath stone contrasted with a rubble stone. The design of the Walters Building is modern, and it was important to use stone in a way that would link to the historic building, whilst using contemporary detailing.
The ashlar walls along with the quoins and trims use Bath Stone from Hartham Park Quarry, finished by Rowland Stone.
There is a large variety of rubble stone used in Clifton, from red sandstones to dark grey pennants. We wanted a warm colour rubble, so selected a mix of Forest of Dean Pennant Sandstone from Barnhill Quarry and Purbeck Traditional Guillotine Cut Building stone from Downs Quarry.
Samples of both stones were erected on the site to assist with mortar choice, and for a final
decision and approval.
The main building is constructed from a steel frame, with timber framed inner walls. We wanted to achieve a high level of insulation, with minimal wall thickness, as on such a tight site every millimetre mattered. The rubble walling was kept to 150mm thick, fixed back directly a ‘Surecav’ backing board to provide a free draining and watertight installation. The cavity is full filled with PIR insulation, with additional insulation within the timber frame.
The stairwell enclosure, housing the new spiral staircase connection from the new link to the existing building, was a major challenge. Two of the external walls are fully glazed, the third is a Bath stone ashlar cavity wall with no additional supporting structure. The ‘Surecav’ backing was used here, with input from the structural engineer on the selection and installation of ties.
A full NBS specification was developed for all aspects of the construction. There were over 40 detailed A1 construction drawings.
As architects we inspected the construction works frequently, and worked closely with the
stonemasons to agree how specific fixings would work practically and appear visually.
