Mastic asphalt is an integral part of our nation’s heritage, with the longevity and waterproofing properties necessary to preserve and protect historic and prestigious buildings across the UK.

Mastic Asphalt Council (MAC) contractor member Howard Evans Roofing has been involved in an impressive project at St Antony’s College which forms part of the University of Oxford. Specialising in international relations, economics, politics and area studies, St Antony’s houses seven research centres focused on Africa, Asia, Europe, Japan, Latin America, the Middle East, Russia and Eurasia. The college has more than 400 students from 77 different countries worldwide.

RCi-September-2020-mastic-asphalt-waterproofingAlthough St Antony’s opened its doors to its first students in 1950, the building dates back to the early Victorian era. Its original use was a convent for the Society of the Holy and Undivided Trinity from 1868. At the end of the 1960’s the college was extended with the addition of the Hilda Besse building – now the site of many of the college’s most important functions such as the dining hall, common room and some classrooms.

The Hilda Besse building is grade II listed and is said to be one of the finest examples of post-war brutalist architecture, having won awards from RIBA and the Concrete Society. In 2019, a wholesale refurbishment of the Hilda Besse building commenced to preserve it for future generations of Antonians. The works were important both 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.

Part of the renovations have included the refurbishment of the Hilda Besse roof. The roof had previously been protected with mastic asphalt and this had provided over 60 years’ weatherproof protection up to this point. In order to replicate the appearance of the original roof and to ensure effective waterproofing for many more years to come, mastic asphalt was specified once again.

The roof has a triangular composition with a rooflight in the middle of each triangle. It is also subject to some foot traffic and it was perceived that mastic asphalt would be more suitable than alternative roofing systems such as single ply or felt.

Howard Evans Roofing won the contract to refurbish the roof in early 2020 working through the main contractor CBRE. When the roof was stripped, it became apparent that the plywood deck was in poor condition. This was replaced and a vapour barrier installed with 100mm insulation and a mastic asphalt roofing system. The mastic asphalt system chosen uses advanced polymer technology to provide the ideal combination of long-term durability, increased fatigue resistance, improved temperature stability and ease of installation.

The project posed some logistical challenges as the Hilda Besse building is situated at the heart of St Antony’s College. Machinery had to be transported to the roof refurbishment area and the mastic asphalt was carried up to the roof using hoists. As the roof has different levels, it proved somewhat difficult to access.

English Heritage visited the site throughout the refurbishment, to ensure that the restoration was carried out sympathetically in accordance with the building’s grade II listing. The heritage market is a key sector for the industry and mastic asphalt is frequently specified by the National Trust and English Heritage, as well as other public and private owners of prestigious buildings for refurbishment projects. Buckingham Palace is testament to the longevity of mastic asphalt. On top of the Royal household is a rooftop of mastic asphalt that has kept the building dry for well over 80 years.

Other challenges on this project included the fact that the refurbishment was carried out during inclement weather conditions with a great deal of rainfall. The renovations also fell within the COVID-19 pandemic.

Howard Evans Roofing worked hard to ensure the roof was watertight before lockdown was implemented. Thereafter, working restrictions were in place to promote social distancing which limited the personnel that could operate on site at any one time.

Excellent collaboration by the project team – which included Nick Restall of CBRE, the Howard Evans Roofing Foreman and manufacturer IKO – ensured that the project continued as safely and efficiently as possible through Covid-19.

In total, Howard Evans Roofing were on-site for a period of six months and the total roof refurbishment extended to over 1,800m2.

Howard Evans, Managing Director of Howard Evans Roofing said: “Mastic asphalt has provided the college with an effective roof refurbishment which mirrors the appearance and aesthetics of the original roof. It will provide an extremely long life and blends in with the rest of the buildings on the site at St Antony’s College. We are very proud to have been involved in a project of this prestigious nature.”

This article featured within the September edition of RCi Magazine – click here to view the full article.