Does an impermeable sub-base need to be laid to a fall?

An impermeable sub-base that is regularly exposed to water requires a minimum fall of 1.5% towards drainage. This applies in external areas such as terraces, balconies and paths, as well as in internal areas including garages and swimming pools.

In this context, waterproof and impermeable mean the same; the technical term for this layer is an impermeable sub-base. The fall allows water to drain continuously to adequately sized drainage outlets or into an infiltration area.

Where standing water or puddling occurs repeatedly, the fall should be checked and corrected where necessary. Standing water can lead to building damage.