The National Research Council of Canada, in collaboration with a Canadian roofing manufacturer, conducted an experimental program to evaluate the durability of SBS-modified bituminous roofing membranes in Canada. This study examined the effect of heat aging on the mechanical and chemical properties of nine commercially available SBS-modified membranes, with emphasis on cold temperature performance. These membranes varied in reinforcements and densities, and were selected to be representative of SBS-modified membranes currently used in Canada. The membrane samples were heat aged in convection ovens at 70±3°C for six months. During this process, some samples were withdrawn at two-month intervals and their tensile properties at 23°C and -30°C, cold flex temperature and glass transition temperature determined. The results confirmed that heat aging mainly affected matrix-controlled properties of the membranes. In addition, the reinforcement controlled the mechanical properties at 23°C but the modified bitumen governed the failure mechanism at -30°C for the polyester reinforced membranes.