Upstand, Warm Roof, WFRL, Waterproofing, Zero Fall Roof definitions

An upstand provides perimeter waterproofing continuity between a flat roof or deck and vertical wall construction, typically 150mm high, but potentially 75mm at accessible thresholds. A warm roof places insulation directly beneath the waterproofing layer. A Water Flow Reducing Layer (WFRL) is a permeable, loose-laid layer in inverted warm roofs to reduce water and fines ingress into insulation. The waterproofing layer forms the primary barrier to water. A zero-fall roof has a finished slope between 0° and 1°.

Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.