SPV Group have completed a major roofing and cladding project using traditional mastic asphalt and leadwork throughout 2020 as part of a larger scale refurbishment project at St Anthony’s College, Oxford.
Working in conjunction with CBRE Construction works began works on the Hilda Besse Building contained within the grounds of this Oxford university college.
Completed in 1970 by John Partridge, the Hilda Besse building sits at the heart of the college, hosting many of the college’s key social spaces, including the dining hall, common rooms and buttery, as well as private dining facilities and kitchen.
The Hilda Besse building is a grade II listed building and is said to be one of the finest examples of post-war brutalist architecture. The building won the RIBA Architecture Award and Concrete Society Award in 1971, noted for its skilful application of concrete in a modern interpretation of a traditional hall.
In 2019 a wholesale refurbishment of the building was commissioned by the collage trust these works were both important for the safety and longevity of the building itself, and to improve its ability to serve the college community. Overall, it is estimated that the total refurbishment will cost in excess of £9 million once fully complete.
SPV Group were assisted CBRE in the renovation of the mastic asphalt roof and the bespoke lead panelling that duplicates on all elevations of the building.
Part of SPV’s Remit was to strip the existing asphalt roof which was at the end of its useful life
The existing plywood deck was defective and required replacement , with SPV supplying and installing a new vapour barrier, thermal insulation and mastic asphalt, creating a warm roof construction.
The main challenge in regards to the project was that all 88 rooflights had to be individually altered to accomodate the new roof design.
A timber frame was created around each rooflight to incorporate a self adhesive bituman vapour barrier, followed by 110mm insulation. Every part of the timber frames needed to be prepared with a sheathing felt followed by expanding metal lath to receive the correct application of the mastic asphalt, as recommended by the Mastic Asphalt Council, the industry body for the correct installation of the material, to provide manufacturers warranties for the installation.
Once prepared, 3 coats of roofing grade mastic asphalt were applied to all of the upstands, with 2 10 mm coats to all flat areas. This was then followed by a 2 coat asphalt fillet finish, which joined the upstands to the flat area using a warm and clean method ensuring a solid seal
The whole roof was then completed with 2 coats of solar reflective paint in heritage grey colour.
Only half this roof was under a temporary scaffold protective roof, adding pressure to delivery as we needed to ensure that the exposed half was sealed at all of the above stages as internal ceilings were being finished underneath by other contractors
Due to the nature of and shape and size of the building, the gutters were laid to falls using the asphalt.
SPV worked closed with The Mastic asphalt council as well as the material manufacturer IKO throughout the works with regular technical and QA inspections being undertaken throughout the project, to ensure that quality standards were met taking into account the difficult nature of the project
In order to maintain and replicate the appearance of the original facade, and to ensure no issues with Planning Permission issues contravened , replacement lead was specified once again as the primary material. In addition to the façade panels there were also bespoke lead box gutters with built in outlets and the façade to the Plant room walls at higher level. The bespoke lead panels were sized from the original panels to ensure originality and that fitment was not an issue, the original lead panels were severely weathered leading to a poor appearance and not in keeping with such a remarkable building. SPV Group’s experienced lead working team created the panels on site and finished with a pre-fabricated lead dome to create the previous ‘button’ feature which doubled up as a form of concealment for the mechanical fixings.
The new Lead box gutters were also created on site to line the detail within façade drainage make up, when originally installed in circa 1940s the downpipe that connected to the bottom of the box gutter protruded through the lead wall façade panel, this pipe was moulded from lead. The original design had an inherent design flaw which caused blockages due to leaves and debris failing and silt forming in the gutter and while the maintenance teams attempted to unblock this subsequently caused damage to the lead lining or in extreme cases most often ruptured the lead welds.
To combat this SPV installed the following as a future proofing measure:
- Welded copper flutes to stainless steel flexible pipe
- welded lead flutes to the copper flutes
- welded the lead flutes the lead box gutter and the outlets
The external plant room walls were entirely clad with lead which required replacing, this posed significant issues as the lead work previously fitted was to a lower standard, the renewal of these lead panel meant the latest LSTA guidelines must be adhered to.
SPV are incredibly proud to have delivered this extremely challenging and interesting project.