The Roof Must Not Leak

Although this is obvious a few people who bought the First Edition thought they cut corners in this area and had leakage within a very short time.

Don’t scrimp on the waterproofing layer and it is very difficult to not use a petrolbased product. If we could we would recommend one but to date we have no knowledge of one that is available. In waterproofing terms EDPM’s are generally considered the most environmentally friendly.

Our experience over the years is that a lightweight pondliner is sufficient for a small scale green roof. The Walter Segal method of waterproofing for self-build uses a pond-liner material. This is the method John used on his first green roof on his own house.

Jon Broome, who has built a number of houses using this method, including on his own house Shaw’s Cottage, where our good friend and colleague Gary Grant designed the roof.

The advantages of a pond liner for small scale builds are:

  • The pipe sleeve [outlet sleeve] for internal drainage can be supplied pre welded to your liner in the position you specify, saving work and detailing for the  builder.
  • Another advantage is also that the complete liner can be fabricated off site and delivered in one piece. This means no specialist onsite work. The waterproofing is simple rolled out and ready to go.
  • A good pond liner has a very long life even when exposed to UV, meaning it will last even longer beneath a green roof.
  • It is light and flexible.

The disadvantage is:

  • Pondliner is not as puncture resistant as other membranes therefore CARE is needed.

You can always go for a superior waterproofing layer and get this in stalled by an approved contractor. EDPM, single ply and

In this case you might want to use an approved contractor. However you might have to argue that the only element you want to purchase from the approved contractor supplier is the geotextile protection layer. Be careful suppliers can try to insist that you buy drainage layers and substrates to maintain their guarantee. Stand your ground.