Fall (Slope)
The deliberate gradient built into a horizontal surface so water runs to the outlets, usually around 1:100 to 1:120 on a terrace.
On an actual building
No waterproofing system is designed for permanent immersion, which is exactly what a flat roof subjects it to. Correcting the fall before laying a barrier is the difference between a system that lasts and one that fails at the low point.
What we most often have to correct
That waterproofing removes the need for a fall. Ponding will defeat any barrier eventually.
Terms that come up alongside this one
- Ponding / Flood Test
Plugging the outlets, flooding a completed waterproofed area and holding the water — typically 48 to 72 hours — while the space below is observed for any sign of ingress..
- IPS (Indian Patent Stone)
A cement-concrete topping laid and floated to a hard monolithic surface, typically 25 to 50 mm thick, used as a screed or wearing course..
- Drip Mould
A groove or projecting profile on the underside of a projection that forces water to drip clear rather than run back along the soffit to the wall..
Fall (Slope) — questions we get asked
What does fall (slope) mean in waterproofing?
The deliberate gradient built into a horizontal surface so water runs to the outlets, usually around 1:100 to 1:120 on a terrace.
Why does fall (slope) matter on a real project?
No waterproofing system is designed for permanent immersion, which is exactly what a flat roof subjects it to. Correcting the fall before laying a barrier is the difference between a system that lasts and one that fails at the low point.
What do people commonly get wrong about fall (slope)?
That waterproofing removes the need for a fall. Ponding will defeat any barrier eventually.
Have a building showing this?
If a term on this page describes something you are looking at, a site inspection will tell you how far it has gone and what it needs. It costs nothing.
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