Green Roofs in Copenhagen - Vand i Byer

The drainage performance of green roofs can be summarised as follows.1. A green roof will typically intercept the first 5mm and more of rainfall (i.e. provide interception storage).2. The amount of storm water stored and evaporated is primarily dependent upon the depth of the growingmedium and type of planting. In the summer a green roof can typically retain between 70-80 per cent of therunoff. [Ref: 3.18]3. In Germany it has been demonstrated that between 40-100 per cent of rainfall can be retained – dependentupon the season. [Ref: 3.20]4. Seventy-five per cent of rain falling on extensive green roofs can be retained in the short term and up to 20 percent can be retained for up to two months. [Ref: 3.21]5.As the rainfall events become longer or more intense, the positive effect of a green roof remains, as there isstill a significant reduction in peak runoff rates. This increase in the ‘time of concentration’ means that a greenroof will be beneficial throughout a wide range of rainfall conditions. [Ref: 3.22]6. The 1 above Green benefits Roofs collectively in Copenhagen mean that, by incorporating a green roof into new development, there will be areduction 2 in Dorthe amount Rømø and cost of the overall drainage infrastructure required to serve that development.London Technical Report