Base layer, thermally activated, bitumen roofing membrane modified with SBS elastomer reinforced with polyester fleece. Bonding of membrane is made during welding of the top layer membrane. Reduces the time of roof waterproofing and can be installed directly on the thermal insulation (EPS, XPS, PIR) while providing the first layer of waterproofing. To be used as a base layer in multi-layer roof coverings and for foundation waterproofing in multi- and single-layer systems. The top side is covered with fine grained mineral granules, bottom side protected with plastic film.