Does a waterproof sub-base (load-bearing layer) need to be installed with a slope?

A waterproof sub-base (technically: a waterproof load-bearing layer) must be installed with a minimum slope of 1.5% towards drainage if the area is regularly exposed to water, for example from rainfall. This applies to outdoor spaces such as terraces, balconies, and walkways, as well as indoor areas like garages or swimming pools. The slope ensures that the water continuously drains to adequately sized outlets or an infiltration area. If water continues to accumulate or puddles form, the slope should be checked and adjusted, as standing water can lead to structural damage.