Part two of our journey of building green roofing will be concerned with drainage layers.
In part one of building green roofing, we talked about the roofing structure and the waterproof membrane. I have taken for granted the fact that you have already achieved planning permission before you began building your green roofing.
A few posts ago, we talked about regulations. Some local councils do not recognise green roofing as calculable for the rating of your property afterwards. Some may insist upon an insulation layer. It is not needed as a part of your green roof per se, but advice should be sought before you go any further, if you haven’t already. It will probably be the case that you can install internal insulation if this is deemed necessary.
Building green roofing is not difficult, but it is complex, involving many layers, (albeit thin ones) – today we will discuss the next few layers, concerning drainage and root management.
On top of the EPDM membrane you should put down a layer of fine gravel. Small stones or pebbles will work best, in a thin, even layer across the roof. Leave approximately 10-12 inches clear around the edges.
Next you will need a rooting membrane. This layer is to prevent roots or mud reaching the lower drainage layer and clogging it up. You can buy this at garden centres or builders merchants and is the material that stops weeds coming through in the garden.
Roll this out over the layer of gravel. Moss can also be used, but this may be an expensive option.
Next you will need to install another fine layer of gravel, which can be raked over to form an even layer across the roof.
Where you left a space around the edges, you will later place larger stones to ensure that the plants do not encroach into gutters or indeed under the membrane and into the property. The other layers that we need to place can go down first, then the finale will be the larger stones, which will also hold everything down and tidy up the edges.
Next time, we will be looking at the moisture layers – essential in building green roofing to stop your plants drying out, however unlikely that may seem in the UK!
Take a look at the other articles in this series…
Part One – Structure & Membrane
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