Iconic Brutalist gem preserved with innovative Sika Sarnafil roof solution

The roof refurbishment of the Central Building at Cambridge University’s Fitzwilliam College is one of the first major projects to use a new, pioneering approach combining Sika Sarnafil’s single ply membrane with large areas of its Sikalastic 621 – a liquid applied product typically used for areas with complex detailing.

This pairing of systems was further enhanced by Sika Refurbishment’s SikaFloor 420, providing a complete building envelope solution.

Working closely with architect Cullinan Studio, Roofing Contractors Cambridge (RCC) and the College, Sika Sarnafil created this innovative waterproofing solution to refurbish the roof, which has an extremely complex design.

Neil Smith, Area Refurbishment Manager at Sika Sarnafil comments,

“The original building was constructed in 1963 by famous brutalist architect, Denys Lasdun. From ground level you can see protruding ‘scalloped’ detailing on the roof. If you looked down on the roof from above, it is like a picture-frame, with the scallops forming the border around the edge of the flat roof. The challenge was to effectively waterproof both the flat roof – which itself had plenty of challenging details – and scalloped areas, while maintaining the look and integrity of the roof and the building as a whole.”

Dave Stewart from RCC continues:

“Due to the unusual shape of the scallops, it wasn’t aesthetically practical to install sheet membrane on them, so many, many discussions took place to decide how best to tackle this!”

“The Sikalastic product ensured these unique details would be protected without altering their shape. It’s not unusual for a project to incorporate small amounts of Sikalastic, but this is one of the first projects where the Sarnafil membrane and Sikalastic 621 have been used over large areas together.”

“For us, the crucial element of this project was getting the seal right. We worked closely with Sika Sarnafil and did multiple tests to make sure the junction between the Sikalastic 621 and single ply membrane was formed using the most effective detailing. The use of Sarnametal created a strong bond between the two products, enabling them to be successfully sealed together. This was by far the most challenging part of the project, but demonstrates how well these products can work together for roofs with incredibly complex detailing.”

It was thanks to the collaborative relationship between Sika Sarnafil’s technical expert and RCC’s highly experienced fitters, that the finished roof met strict requirements of the architect and client.

Alex Abbey from Cullinan Studio wanted the works to be sympathetic to the original building.

“We were keen to minimise weight on the roof and wanted to steer clear of asphalt and the like, so Sika Sarnafil’s lightweight products were ideal.”

“We needed a product that would not only effectively waterproof but that would sit over the copper scallops and maintain the shape’s detail. The Sikalastic 621 proved ideal and worked in harmony with the Sarnafil membrane. As did the SikaFloor 420, which was used on the façade and underside of the scallops – a complete solution from Sika. And importantly, the completed roof was awarded a Sarnafil Plus guarantee by Sika, a must for the client, preserving the building as an architectural landmark and study area.”