TPO

A factory-manufactured polymeric waterproofing sheet, typically EPDM, TPO or PVC, installed in a single layer and joined at laps by welding, adhesive or tape. Single-ply systems may be mechanically fastened, fully adhered or ballasted, and are widely used on flat and low-pitched roofs.

Ethylene propylene diene monomer (M class) rubber, a synthetic elastomer with excellent resistance to ultraviolet light, ozone and weathering. In roofing it is used as a single-ply waterproofing membrane, often supplied in large prefabricated sheets, and it is also widely used for seals, gaskets, hoses and glazing profiles in the automotive, marine and industrial sectors.

A single-ply roofing and waterproofing sheet based on plasticised polyvinyl chloride, usually reinforced with a polyester or glass fibre scrim and joined by hot-air welded seams. PVC membranes are flexible and easy to detail, though plasticiser migration and incompatibility with bitumen and polystyrene must be addressed in design, typically with separation layers.

The overlap between adjacent sheets of roofing membrane or underlay where they are joined and sealed, by heat welding, solvent welding, adhesive, tape or bitumen bonding depending on the material. Lap integrity determines the watertightness of sheet systems, so minimum lap widths and the staggering of end laps are specified in system guidance.