drainage for green roofs

Green Roof Drainage

Learn how to correctly drain a green roof

drainage on a green roof on a new house extension

New Builds

A step by step guide to creating a SAFE and LEAK FREE green roof on a new small scale construction project. Learn from the vastly experienced authors how to accomplish it yourself or provide guidance to your contractors

draining a retrofit green roof


Even the smallest of roof spaces can provide a small haven of beauty and a wildlife oasis. The retrofitting section advice can be used on garden sheds, cycle & bin shelters, the fundamentals remain the same!

edge drainage details on a DIY green roof


From suggested screw sizes through edge details to drainage suggestions, John & Dusty take you through the process using text, photos, illustrations and videos

Green Roof Drainage – Allowing Rainfall To Escape

A lack of water is one of the biggest stresses for a green roof of any size, anywhere. However, too much water retained on a roof can cause a number of serious issues that need to be avoided or mitigated:

  • Potentially overloading from the increased weight of water,
  • Vegetation that does not like anaerobic conditions can be killed off by excess water.

How to best drain a small green roof?

One of the main concerns that small scale builders have outlined to us is how to integrate green roof drainage to adequately to cope with rainfall of all quantities. In the guide we give rational and simple advice and instructions on the whys and hows of building in appropriate drainage systems.

In the era before commercial drainage layer materials were developed, it was common practice on green roofs to use a thin layer of gravel to act as a drainage layer. The issue with gravel however, is that it is relatively heavy. Thus, in the guide we explore alternative, innovative and creative ways of dealing with drainage for green roofs while also adding to the visual landscape design and increasing the biodiversity potential of the roof.

Utilising a Gabion Roof Edge to help with green roof drainage.

Making a gabion edge to help with rainwater drainage on a small green roof

While you’re on the subject, please also check out our article Vertical Drainage on a Green Roof which looks at some of the novel and interesting ways of dealing with the ‘down’ after the ‘off’.