Specifier Review
Green roofs store rainwater in the plants and growing medium.

Can Green Roofs Reduce Storm Water Run-off?

As part of a sustainable drainage system strategy, it is essential that we find and implement alternative solutions to preventing localised flooding. In built up areas 95% of the ground surface is sealed. Though we’ve all seen examples of front gardens being concreted over for parking purposes, it is worth noting that roofs represent nearly half of impermeable surfaces in urban areas. This means any excessive amount of rainwater has nowhere to go to apart from our inadequate drainage systems or to the poor souls further down along the watercourse.

Green roofs are good at retaining rainwater

How Can Green Roofs Help?

Compared to a conventional roof, an established green roof can reduce total rainwater run off by a significant volume. It is estimated that green roofs will retain up to 80% of rainfall during the summer months and up to 35% during the winter months. The drop off is partially due to less plant growth during the colder months and the fact that there is generally a higher amount of rainfall during the winter months. This of course will vary depending on regional weather patterns, type of vegetation and the particular type of green roofing system.

Summary of green roof benefits

  • Green roofs store rainwater in the plants and growing medium.
  • They steadily evaporate water back into the atmosphere
  • Green roofs are good at retaining water
  • They reduce and delay run off during times of prolonged heavy rainfall
  • They help to reduce the burden on our drainage systems
  • They help to reduce sewage discharge into our water systems
  • As the plants grow, the green roof system will hold more water
  • The stored water is released slowly back into the environment

There are many other benefits of installing green roofs, but just this small list would suggest they have a significant role to play in UK flood management.

If you are considering a green roofing project of any size, then please contact Riefa Green Roof on 0844 057 0359 to discuss your living roof project. We’re happy to give advice and can supply everything you’ll need for your green roof, including a root resistant membrane, your sedum and importantly your lightweight,  organic green roof growing medium (IGV GmbH approved and accredited)



Green Roof