Dimensioning: Average buffer height of 60 mm (taking the slope level of the roof into account)
Application: Flat roofs
Advantage: Can be placed on almost any flat roof
Disadvantage: Waterproofing requires additional attention
Flat roofs can be designed to buffer a degree of precipitation by situating the drain at a slightly higher level. This needs to be taken into account in the roof’s construction (greater load). This type of water roof is called a water roof for rainwater retention. The water only remains on the roof for a short period of time after rainfall. The rainwater is drained off at a delayed pace using a narrower lower situated opening. The water needs to be drained off to create sufficient storage capacity in time for the next rainfall.
Contrary to what some people assume, the cooling effect of the water on the underlying rooms is only temporary and does not always occur at the preferred moments. Water roofs for cooling purposes are not the same as water roofs for rainwater retention. Whereas water roofs for rainwater retention are designed to be emptied in time to buffer water during the next rainfall, cooling water roofs in fact retain the water and allow it to evaporate slowly.
The optimum situation would be for the water management of these roofs to have an electronic interface with the weather forecast and discharge the water before the next rainfall, as this would allow both functions to be combined. Such electronic control systems are already used for green roofs.
A water roof for cooling purposes keeps the building below cooler, and the evaporation means that the immediate surroundings are also cooler. One drawback is that it is impossible to guarantee that sufficient rainwater is available at all times, however; once the rainwater has evaporated, drinking water or sufficiently high- quality surface water will have to be pumped onto the roof.