Abstract: The present invention includes a system for insulating and waterproofing wall structures, floors and roofs. A plurality of bentonite clad extruded expanded polystyrene sheets, each extruded expanded polystyrene sheet having a bentonite clad major surface and bentonite clad side surfaces are positioned such that the side surfaces form water resistant seals between adjacent extruded expanded polystyrene sheets. When used to waterproof a wall structure, the major bentonite clad surface of the extruded expanded polystyrene sheets faces the exterior wall surface of the wall structure. When used in a floor construction, the bentonite clad major surface faces upwardly and is in contact with the cementitious layer of floor material positioned on top of the extruded expanded polystyrene sheets. In a roof construction, the extruded expanded polystyrene sheets are disposed on a base roof layer with the bentonite clad major surface facing upwardly and being disposed in contact with a layer of roofing membrane.