To provide a heat-insulating waterproofing construction method excelling in appearance causing no level difference of a heat insulating layer to appear on the surface of a waterproof sheet even when there is unevenness on backing because of using polystyrene foam as a heat insulating material in the heat-insulating waterproofing construction method.

The heat-insulating waterproofing construction method for installing the heat insulating layer 2 on the backing 1 and laying the waterproof sheet 3 thereon, uses polystyrene foam as the material of the heat insulating layer 2, arranges a plurality of heat insulating layers 2 side by side, and interposes a slope member 4 between the heat insulating layers 2 and the waterproof sheet 3 so as to straddle the adjacent heat insulating layers 2 in the adjoining part of the heat insulating layers 2.