PURPOSE: To ensure the easy execution of work by bonding an asphalt sheet laminated with a thermoplastic resin sheet and a fibrous sheet on the upper surface thereof and a perforated sheet on the lower surface, onto a waterproof base material, and finally covering the uppermost surface with a waterproof film.

CONSTITUTION: A lamination sheet 4 comprising a perforated polyethylene sheet 3, a thermoplastic resin sheet of polyethylene and a fibrous polyester unwoven cloth of fibrous sheet is laminated on both surfaces of an insulation asphalt sheet 5, thereby forming a 4-layer film insulation sheet 6. Furthermore, the sheet 6 is bonded to a waterproof base material and finally a urethane film is applied to the uppermost surface for waterproof structure. According to the aforesaid construction, economical effect can be enhanced.