Water Runoff
Green roofs can form part of an effective sustainable drainage (SUDS) solution by reducing the amounts of storm water run-off and attenuating peak flow rates. Consequently, this proven source control technique reduces the downstream need for expensive underground drainage infrastructure and also cuts the risk of localised flooding events. In the summer a green roof can typically retain between 70-80 per cent of rainfall run-off.
Research from around the world indicates that green roofs reduce annual run-off from roofs by at least 50%, and more usually by 60-70% - contributing to urban drainage and flood alleviation schemes. Moreover, the rate of release following heavy rainfall is slowed, reducing the problems associated with storm surges.
With an increasing need for developments to have limited water run off, the Environment Agency now highlight the use of green roofing in their May 2003 publication "Sustainable Drainage Systems (SUDS) - an introduction" and the Agency have been supportive of supplementary planning documents which refer to green roofs – such as the Leeds Biodiversity and Waterfront Development SPD (2005).
