The main task of the drainage layer is to drain the surface water seeping through from above to the roof drains. In addition, depending on the formation and layer structure, the drainage layer can also serve as a water storage layer or to enlarge the root area. The drainage layer can consist of profiled or studded panels made of plastic or rubber, but also of bulk materials such as gravel, chippings, lava or expanded clay or special foam or textured fleece mats.
Source: bauwion
