Project Brief
We were instructed to complete a RAAC survey of the flat roofed areas of the building and provide structural advice on the options for removal, remediation, and/or ongoing management. Constructed in 1974 using traditional masonry, a general survey of the existing building had identified the presence of Siporex roofing units supported directly from the masonry over the building’s communal areas. Siporex is a trade name for RAAC panels.
Solution
Our approach followed published IStructE RAAC Guidance. We obtained access to the roof and reviewed historical photos taken during its original installation. We collated detailed documentary evidence of the RAAC roof panels into a Survey Report. This contained an area plan and associated descriptive notes and photographs describing the RAAC’s condition on a room-by-room basis. Evidence included:
- Length and direction of spans
- Measurement of deflections
- Recording of cracks and defects
- Recording evidence of water leaks and associated damage
- Hammer tap testing for signs of debonding concrete
- Recordings of panels cut after manufacture
- Recording of any alteration or penetration through panels after construction
- Investigating plank end supports – this was achieved by drilling the bearing points to confirm their length and the location of longitudinal reinforcement.
We used our survey findings to make a thorough initial Risk Assessment, categorising risks using the Red/Amber/Green classification rating in IStructE guidance, where RED = critical/high; AMBER = medium, and GREEN = low risk. The most notable risk with RAAC planks is their potential for sudden shear failure. We determined the Risk Assessment category based on the:
- Condition and length of supports/bearings
- Water ingress being observed
- No water ingress being observed
Our report provided conclusions and recommendations based on our client’s immediate and long-term needs. As the building would only be operational for another 4-5 years, we advised that replacing the RAAC panels and roof waterproofing was not practical or cost-effective. We recommended alternative remediation works to allow safe use of the building for this period, primarily for:
- Cut or modified panels – roof light openings had been created in several locations post-installation, which carried a risk category of RED. For safety reasons, we advised that this RAAC must be strengthened or propped before allowing people back into the building. We produced detailed notes and a structural strengthening design for essential remedial works under the openings. Our design comprised dimensioned details of new steel channel supports, timber packing, resin anchors and bolt sizing. We did not recommend propping the openings long-term as this would restrict access.
- Areas of deflection and water ingress – away from the panel openings, these areas were not significantly concerning. Classifying these as AMBER, we recommended completing an annual inspection to check for any further deterioration in condition and movement into the RED risk category.
- Roof waterproofing – we recommended patch repair works to the surface and around the openings.
“We were very pleased with the RAAC survey and strengthening design works undertaken by Adept which has allowed us to keep the church open to the public. They attended site and undertook the required intrusive investigation works with minimal disruption and damage to the building, and issued the report and strengthening works design promptly”
Robert Burgess
