To seal completely a gap of an overlapping part of roofing by a method wherein an adhesive surface is provided at least on one side of a belt-like base and a material of high water absorption properties continuous in the longitudinal direction of the base is stuck on the adhesive surface.

An adhesive layer 12 being formed on one side of a base 11, threads 8 (or knit 9 or fabric 10) of fibers of high water absorption properties continuous in the longitudinal direction of a tape are stuck on the surface of the adhesive layer 12 and the surface thereof is covered with release paper 13. On the occasion, the base 11 is constituted of a synthetic resin film or a material of nonwoven fabric, paper or a composite thereof having waterproof properties. As for the material of high water absorption properties, a macromolecular polymer constituted of a vinyl alcohol acrylate copolymer, for instance, which absorbs water in contact therewith and swells, is used. In the case when the release paper is not provided, a silicon coated layer 14 is formed on the surface of the base 11. Since the material of high water absorption properties seals a gap of the adhesive surface completely in continuity in the longitudinal direction, according to this constitution, penetration of water across the waterproof tape can be prevented.