Membrane lap

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.

A sheet waterproofing material comprising a polyester or glass fibre carrier coated with oxidised or polymer-modified bitumen, normally installed in two or more bonded layers on flat roofs. It is the modern UK term for what was traditionally called built-up felt roofing.

A localised element of a roof or below-ground waterproofing system where the continuous field membrane is interrupted or terminated, such as upstands, penetrations, outlets, movement joints and edges. Details demand specific design and careful workmanship, and they are where most waterproofing failures originate.

The suction force exerted on a roof by wind flowing over and around a building, greatest at perimeters and corners. Roof systems resist uplift through mechanical fastening, adhesion or ballast, with design loads derived from wind actions codes and system resistance established by testing.