Roof fall is the slope directing water across a roof surface towards an outlet. It describes the geometry of the substrate or build-up, rather than the covering material.
What does this mean on your roof?
A flat roof therefore need not be literally horizontal. Assessment considers the water route and any local depressions.
One photograph of a puddle, without rainfall and timing information, cannot establish complete drainage behaviour. Record recurring locations from a safe position rather than walking onto the roof to measure them.
A renovation proposal should state whether existing falls will remain or change. An additional membrane does not automatically correct unsuitable geometry. Ask how the proposed assembly meets outlets and upstands, because height changes may affect these connections. The appropriate design requires assessment by the responsible professional using the actual roof configuration.
Frequently asked questions
Is roof fall the same as an outlet?
No. Falls direct water across the surface; outlets carry the collected water onward.
Can falls be established from a photograph?
Photographs may provide clues but do not replace measurement or assessment of the drainage arrangement.
Consulted 19 September 2026. Check requirements for your own address and selected system.