Background

Green roofs are roofs that have been especially fitted or designed to support a shallow-growing vegetation such as sedem or meadow grass on the roof's surface. Green roofs emulate a natural environment on the roof's surface, attenuating and retaining rainfall. This categorizes them as a Sustainable Urban Drainage System, effectively reducing the impermeable area of a catchment.

As population density increases, and urban impermeable cover increases, sewer designs of the last 50 and 100 years are becoming inadequate for normal flows. Climate change compounds this problem, resulting in increased flood volumes and frequencies. With the average lifetime of a given section of sewer in the UK being 1,000 years, any effort to alleviate load on the network should be investigated.

Green roofs will decrease the amount of water that needs to be treated at the sewerage treatment works, as well as potentially improving the run-off quality. This will reduce load on the entire system and result in lower costs and cleaner water spilling into rivers when the network does overflow. In networks where stormwater does not flow into the sewer, local flooding will be reduced.

The data presented on this website in the format of graphs help to illustrate the time delay and retention or the difference between rainfall and run-off, caused by the roof. This is influenced by a variety of factors such as humidity, temperature, the last time it rained, as well as roof configuration.

More information is available at The Green Roof Centre.