Abstract: A roof system comprising a roof substrate with an exposed vertical, rigid drain pipe is covered by a flexible single ply synthetic, plastic cover, with a sandwiched reinforcement fabric, having an opening in alignment with the drain pipes. A patch-shaped piece of the cover material has a drain pipe accommodating opening surrounded by an edge portion perimetrally pressure-heat welded to the cover, the piece having a generally rigid, non-bindable, plastomeric seal ring disc, formed generally of recycled such cover material wherein the reinforcement fabric is disassociated and present in the plastic in the form of randomly dispersed fibres. The disc is only centrally pressure heat-welded to the underside of the piece and has an opening therethrough of substantially the shape and size of the drain pipe. It is the ring disc which is secured to the substrate.