Waterproof coverings for generally flat or low-pitch roofs on buildings

A waterproof cover having special utility for a flat or low-slope roof for a building. The roof includes a structural part comprising beams, joists, rafters, etc., as well as a substrate in the form of plywood panels, metal decking, etc. A waterproof cover is secured over the substrate. The cover is formed by placing a plurality of waterproof sheets loosely over the structural substrate, and connecting the abutting edges of adjacent sheets to one another, much like an old-fashion quilt is assembled. The preferred sheets constitute lightweight, thin but relatively stiff sheets of resin-impregnated fiberglass having a thickness of about 0.065 inch; and the joints between adjacent sheets are formed in situ by a mixture of fiberglass fibers and cured resin. The plurality of sheets are joined to one another (along their abutting edges) to form one giant waterproof cover. To accommodate dimensional changes that will inevitably arise during the life of the cover, there is deliberately built into the cover an excess of material that can compensate for anticipated contractions and expansions due to thermal changes, foundation shifting, etc. This excess of material is created by placing a plurality of removable supports under the sheets before they are mechanically anchored to the substrate. The preferred supports are ropes which can be strung out both longitudinally and transversely on top of a substrate before the sheets are initially put into position; after the sheets have been securely anchored to the substrate, the ropes are then pulled out.