Until recently, using asphalt to adhere roofing materials was likely the most popular attachment method. It was used for everything, from vapour retarders and insulation, to the thermal barrier and cover board. Even roof membranes were bonded in asphalt—the first ply of a two-ply modified bitumen (mod-bit) roof membrane or the entire four-ply ‘tar-and-gravel’ system got their share.