Fire Performance of Cedar Shingles under Radiant Heat

Wood as a building material is a common roofing material in both contemporary homes and older properties such as heritage buildings. As a combustible material, wood can be associated with higher rates of building damage from wildfires. This study investigates the spontaneous ignition of contemporary Eastern white cedar shingles (Thuja occidentalis), a commonly used roofing product in older houses and heritage properties in Ontario. The samples were tested with a cone calorimeter under radiant heat without a spark igniter. The samples were conditioned under three moisture content categories: (1) ambient; (2) dry; and (3) wet. They were tested using incident radiative heat for 15 min or until 2 min after flameout under three heat fluxes: (1) 20 kW/m2, (2) 30 kW/m2, and (3) 40 kW/m2. Moisture content and heat flux had a clear impact on ignition and pyrolysis. All samples ignited at 40 kW/m2 and the dry samples ignited at 30 kW/m2. In samples which did not ignite, indicators of pyrolysis such as off-gassing, charring, and ember formation were delayed as the moisture content increased. However, dry samples at 40 kW/m2 had a slower average ignition time by 20 s and a lower average peak HRR than the ambient samples by 8 kW/m2. It was posited that it could be due to the char layer forming faster at the lower moisture content, creating a protective layer that delayed ignition. Future research will investigate the impact of incident heat flux and moisture content on piloted ignition of cedar shingles via firebrands, which is common during wildfires. Research to evaluate the performance and ignition of heritage cedar shingles versus contemporary cedar shingles is also recommended.