A roofing system including two techniques that confer water tightness to exposed substrates, whether cimentious or not, used on roofs of current buildings. The system increases reliability of the surfaces against the percolation of water. The system includes the process of applying, on exposed porous or non-porous surfaces (1), mud slab, regularized or not, of concrete, wood, metals, etc., on top of baseboards or parapets (2), a high adherence organic resin (4), that is self-leveling, visco-elastic, thermoplastic and hydrophobic, covered by film strips (5) of aluminum laminated with thermoplastic copolymers, thermally welded at its overlaps (7) by a thermal process and fastened in the vertical surfaces of the structures by groups (6) of screws, plastic washers, and expansion shells. The flow of rain water is guided by pipelines (3) of PVC or other equivalent material.