Ponding does not affect the performance or life expectancy of single ply membrane waterproofing. Nor does it typically affect the guarantee offered by the waterproofing manufacturer. However, all efforts should be made to avoid ponding.
When flat roof drainage falls are not properly designed or constructed, the roof becomes less effective at shedding rainwater. Any areas of the roof that do not drain correctly lead to pools of standing water – which is known as ponding.
Why should ponding be avoided on a single ply flat roof?
The roof structure is designed with certain structural loads in mind. Since a flat roof is expected to drain freely, the weight of pools of rainwater are not among the loads accounted for. Extra stress is therefore placed on the roof structure.
Ponding water is also visually unappealing, and leads to a build-up of silt and algae which is dangerous to anybody accessing the roof for maintenance. It presents a further health and safety risk in winter, when it can freeze.