Prefabricated waterproofing membrane composed of distilled bitumen and polyalphaolefin polymers (APAO) reinforced with heavy duty, thermostabilised, non-woven spunbonded polyester fabric that gives the membrane high mechanical properties and good dimensional stability. The waterproofing mass is added with special non-toxic inorganic compounds which give the product a flame-retardant action. For polyolefin membranes without mineral self-protection consisting of slate, intended to be used as a top layer, always provide for periodic surface protection with protective reflective paint. The self-protected version with slate chippings on the upper surface reduces the absorption of heat on the surface thus improving the durability of the membrane. The self-protected versions are provided with a lateral overlap.