Prince Henry’s High School in Evesham is an Ofsted ‘Outstanding’ Academy for students aged 13 to 18 that has worked collaboratively with chartered building consultant, PR Associates, and roofing systems specialist, Carlisle Construction Materials (CCM), to secure a Condition Improvement Fund (CIF) grant for a roof upgrade.
Carlisle Construction Materials
The project involves a thermal upgrade to three roof areas, totalling 1100m2, along with an overlay with CCM’s RESITRIX system; a single layer system that combines bitumen and EPDM roofing technologies. The roof refurbishment also involves improvements to drainage to address issues with ponding water.
Despite the challenges of the pandemic, the project is now well underway, with phases one and two complete, and phase three to take place during the summer break.
The school campus is typical of many high schools, with multiple additions to the original main building. Consequently, there are a number of different roof levels and roof areas in varying conditions, with a mix of existing coverings that had reached the end of their service life. In some areas, the roof was leaking and a small roof area over the main entrance was in need of particularly urgent attention because rain was draining onto it, resulting in ponding water.
PR Associates advocates CCM’s RESITRIX roofing system for school roof refurbishment projects. The hybrid modified bitumen and EPDM membrane offers torch-free installation and a certified service life of more than 50 years. The chartered building consultant worked with CCM to develop a technical specification, which contributed to Prince Henry’s High School’s CIF application.
“We often find that a collaborative approach between the school, the building surveyor and our technical team at funding bid stage is instrumental in outlining the business case for a CIF grant,” explains Frank Turner, Technical Adviser at CCM. “Carrying out a full condition survey and providing a technical specification at this stage ensures that the bid considers the full scope of works and that the school makes decisions that will reduce future maintenance costs and disruption.”
Site audit and specification
CCM’s site audit was carried out with the contractor, AJR, present to establish the existing roof build-up and condition. The existing build-up is a profile metal deck, with a vapour control layer, 30mm of EPS insulation, 20mm of fibre board and a bituminous membrane.
CCM’s technical team carried out penetration tests to ensure there was no water tracking under the existing coverings. The audit revealed that the majority of the roof areas could be overlaid following preparation with jet-washing, with a requirement to cut out blisters in some areas and carry out patch repairs. For a limited area of the roof, the existing bitumen membrane was so degraded that it had to be stripped out and a new air and vapour control layer (AVCL) was installed. For most of the roof areas, however, the audit confirmed that the prepared existing roof covering could be used as the AVCL.
Frank Turner continues: “Compatibility and ease of installation as an overlay are key advantages of the RESITRIX system. This is particularly important for school roof refurbishment projects, because it helps to reduce the length of the programme and potential disruption by avoiding strip-out, provided the existing covering is properly prepared. Using the existing covering as the AVCL also saves time and cost and RESITRIX only needs a primer and a single layer to complete the new roofcovering.”
To upgrade the roof’s thermal performance as part of the refurbishment, a tissue-faced insulation was specified for installation directly onto the existing roof surface. For the phase one and two roofs, a 130mm flat insulation board has been specified, but a tapered insulation scheme will be used for the phase three roof due to issues with drainage, which have been causing ponding water. Once the insulation has been installed directly onto the prepared roof surface, the specification requires application of CCM’s FG 35 primer, which is applied directly into the insulation board. This activates the adhesive on the RESITRIX membrane as soon as contact is made when the system’s release film is peeled off, with no requirement for heat activation or mechanical fixings.
The specification requires a 50mm lap for the join between each 1 x 10m roll of RESITRIX laid out onto the roof. Each lap must be sealed using a hot air welding tool and, for this project, an automatic welding tool is being utilised, following a test weld. The roofs involve a range of details, including rooflights (which are being replaced), drainage outlets, a parapet wall and a tank room. A number of rainwater/ overflow outlets will also be installed to CCM installation guidelines. For most details, the AJR team can use offcuts of the membrane to form these details because the RESITRIX material bonds to itself.
Building on experience
With the specification agreed and the CIF funding secured, the roof refurbishment at Prince Henry’s High School is being carried out as part of a wider programme of works. The AJR team has been trained in installation of the RESITRIX system and CCM’s technical services team is carrying out regular site inspections to ensure project delivery matches the specification and delivers the full performance potential of the system.
Andy Robinson from AJR comments: “We have a team that is very experienced in various roofing membranes but the RESITRIX training CCM provided highlighted just how easy it is to install. Thanks to the EPDM layer, the system retains its elasticity, even at low temperatures, and the membrane bonds permanently to the roof on contact with the primer. It also allows us to form details with the offcuts, so there is virtually no waste.”
Richard Pill, Chartered Building Consultant and PR Associates adds: “We recommend RESITRIX for school projects because it not only offers excellent performance for an extended service life but it enables installation in an occupied school building with no hot works or unpleasant odours.”