Prefabricated modified composite waterproof membrane with differentiated waterproofing compounds. The upper face waterproofing compound is composed of distilled bitumen and elasto plastic polyolefin’s with high heat resistance and cold flexibility, while the lower face compound is composed of distilled bitumen and special polymers which give incomparable characteristics of adhesion to old membranes with mineral self-protection. A particular compound, specifically studied, is used to make the upper and lower face compounds compatible. The particular reinforcement used in the ITER 20 R G200 Mineral, a woven fiberglass mat, provides the membrane with incomparable dimensional stability and exceptional mechanical characteristics. The ITER 20 R G200 Mineral membrane is finished on the upper face with a white reflex mineral slate with good reflective capacities, besides extending the life expectancy of the membrane, its reduces heat buildup both on the external surface as well as inside the building with a reasonable savings in terms of energy consumption. The emissivity of the ITER 20 R G200 Mineral furthermore favors the dissipation of accumulated heat during the night. The lower face or application surface has a PE film finish.