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Paving over natural surfaces has a particularly negative effect on water balance. Rainwater can no longer seep away unimpededly, which means that less groundwater is formed. In addition, the risk of flooding increases, because many sewers can no longer cope with water that accumulates during heavy rainfall. This can lead to local urban flash floods (UBA, 12.02.2020). Green roofs cannot replace depaving, but they can be a major contribution to decentralized rainwater management in cities. Green roofs store water during rain events, evaporate part of the stored water and release the excess water slowly into the sewer system. This eases the pressure on the sewage system and may prevent or at least reduces the impacts floods.
In addition to water retention, green roofs offer many other advantages such as increased biodiversity, temperature reduction, evaporation, noise reduction and amongst others. For the first time in Germany, the Bundesverband GebäudeGrün e.V. (BuGG) published with the “BuGG-Marktreport GebäudeGrün 2020“, an overview of the latest figures on roof, façade, and interior greening.
A survey of the total market of annually newly greened roofs has been carried out. For this purpose, substrate manufacturers and suppliers were asked about the quantities of the following substrate types supplied in Germany: extensive substrate single-layer and multi-layer, intensive substrate single-layer and multi-layer. With the determined delivery quantities and via fixed assumptions on the installation heights of extensive and intensive green roofs in single- and multi-layer construction, the overall newly greened green roof areas can be estimated.