Protected membrane roof system for high traffic roof areas

Claim 1

A roofing system comprising a roof deck, a waterproof membrane above said roof deck, a plurality of extruded panels of foam plastic insulation above said waterproof membrane, each of said foam plastic insulation panels having peripheral edge surfaces and having a planar lower surface and having a plurality of flat topped integrally extruded parallel raised elongated ribs on the upper surface thereof and spaced apart by grooves, said ribs being stiffer, stronger, and more resistant to deformation than the remainder of each panel, the tops of said ribs forming a discontinuous planar surface substantially parallel to said lower surface, a waterproof plastic film having peripheral edges coincident with the peripheral edge surfaces of a respective panel and being coextensive with and bonded to only the lower surface thereof and resting on said waterproof membrane in an unsecured face-to-face contacting relation, each of said panels being otherwise free of plastic film and exposed to ambient air for evaporation of moisture, said plurality of panels having said peripheral edge portions and said film peripheral edges in substantially abutting relation, and a plurality of concrete panels overlying said foam plastic insulation panels and resting on said rib top discontinuous planar surface.