THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ORN 14 ONTARIO ROOFING NEWS – ISSUE 2 2026 Roof Remediation GETTING THE EXTERIOR BUILDING PRODUCTS YOU NEED ... Specialized in easy. HAS NEVER BEEN EASIER. Roofmart.ca Assessment and Management of RAAC The first step in identifying RAAC panels in Ontario buildings is to look at the age of the build- ing. As noted previously, RAAC was only sold in Ontario from the mid-1950s to mid-1970s; therefore, buildings built outside of this range are unlikely to have been construct- ed with RAAC. If available, build- ing records may clarify the materials used in the building. Following this preliminary step, RAAC can be visually identified as follows: • Size: Siporex floor and roof panels were typically manufac- tured to be 457mm (18”) wide, 76mm to 254mm (3” to 10”) thick and with lengths up to 6.1m (20’3”). Wall panels are typically 457mm (18”) wide or 1,524mm (60”) wide, 127mm to 254mm (5” to 10”) deep and up to 6.1m (20 ft) long. Masonry blocks are typically 229mm by 457mm (9” by 18”) and available in thickness from 75mm to 254mm (3” to 10”). • Shape: RAAC panels typi- cally have a chamfer or V- shaped groove at the edge of the panels. • Colour: Light grey or off-white. • Texture: Smooth or slightly textured surface. Porous/ bubbly interior with no vis- ible stones or aggregate. • Weight and density: The weight varied from 9-30 lbs/ft2 and the density is approximately 25-37 lbs/ft3 (pcf), which are 20-25 per cent of normal rein- forced concrete. It produces a somewhat hollow sound when tapped with a hard object. • Strength: Compressive strength was originally speci- fied to be 300-700 psi (25- 37 pcf). • Bowing and deflection: RAAC roof panels may bow or deflect. This can be most easily observed when there is differential bowing from one panel to another. Siporex lit- erature denoted a maximum deflection of 1/360 of the ef- fective span under the weight of applied loads. • Softness: RAAC is soft and can more easily be scored with a screwdriver, screw or nail. Once RAAC has been identified at the building, periodic structural assessments of the panels should be conducted by a licensed structural engineer. The structural assessment should include a review of deadload, including any potential changes to the loading on the roof such as the roof assembly and/or mechanical equipment on the roof, measure- ments of deflections and end bear- ing distances, recording of defects including differential displacement, cracks, spalling, water leaks, reso- nant sounding of panels for evi- dence of debonded steel reinforce- ment and recording of alterations made post-construction. Localized intrusive openings and in-situ load testing can also be completed, with consideration for the potential damage that could be caused to the structure.10 Consideration should also be given to an engineered snow removal plan to reduce loading on the roof. Based on the results of the assess- ment, the individual panels can be categorized based on their risk level. The report prepared by Rimkus rec- ommends four risk categories: critical risk, high risk, medium risk and low risk. Low-risk panels are recommend- ed to be reassessed every three years, and medium-risk panels should be reassessed annually. High-risk pan- els should be replaced or reinforced before winter. Critical-risk panels should be closed off and shored until panel replacement is completed. Periodic roof condition assess- ment and moisture testing should also be performed by a qualified building enclosure consultant in conjunction with the structural assessment. Roofing assessments should include thermographic im- aging, electrical capacitance and destructive cut tests with moisture probe equipment. The presence of RAAC construc- tion is likely to affect more than just the school boards and other public entities that are currently implement- ing management programs for these structures. This article has provided a high-level overview of the issue at hand, but those interested in learning more about the topic are encouraged to review the references listed below. In particular, the engineering report prepared by Rimkus for Infrastruc- ture Ontario presents a very relevant summary of the information for an Ontario context. References 1. Rushowy, K. (2024, June 27). Hundreds of Ontario schools with the same aging concrete Steel corrosion in RAAC.9
View this content as a flipbook by clicking here.