To provide a heat-insulation waterproof structure which is formed of a resin foamed body and excellent in heat insulation properties and solvent resistance, and to provide a heat-insulating waterproofing method.

The heat-insulation waterproof structure 1 is formed by laminating at least a heat insulation material 5 and a vinyl chloride resin sheet 6 on an underlayer surface 2 of a construction. The heat insulation material 5 is obtained by foaming a resin composition containing: a copolymer (A) formed of an aromatic vinyl unit, an unsaturated dicarboxylic acid anhydride unit, and an N-alkyl-substituted maleimide unit; and a copolymer (B) formed of the aromatic vinyl unit and a vinyl cyanide unit.