Construction: Build Up
A green roof consists of 3-4 thin layers of materials that work together to protect the waterproofing against root damage, ensure good drainage and provide the plants with the growing media and the small amount of moisture they need to thrive.
The build-up described in this section is suitable for use on a domestic roof smaller than 50 square metres eg a garage or an extension. This is also the build-up to use on sheds, summerhouses, log cabins or garden rooms - provided that the building is strong enough (see structural requirements: loading).
For commercial roofing or for domestic roofs over 50 square metres, a slightly different build-up may be appropriate. Please contact us.
Provided that the roof meets all structural and design requirements, build-up is as follows:
- Roof deck
- Waterproofing
- Root barrier
- Drainage mat - for slopes between 1 and 3 degrees
- Water retention matting
- Sedum matting
- Wind uplift protection
- Detailing
For pictures and diagrams of green roof build-up please click here.
Roof Deck
Must meet structural requirements, be free of debris, and have a relatively smooth surface - there must be no air pockets beneath the green roof build-up.
Waterproofing
Must be in good condition - it's very difficult to make repairs once the green roof build up is in place.
Root barrier
Use buyl pond liner or similar to ensure that sedum roots cannot damage the integrity of the waterproofing… on a simple green roof, eg a wooden garden building, the butyl layer can be used as both waterproofing and root barrier.
Drainage mat
Essential on roofs where the slope is less than 3 degrees. Sedum plants will not survive in poorly drained conditions; Drainage mat ensures that excess water can safely run off the roof.
Water retention matting
Use on all roofs, it's an inexpensive way of collecting and storing rainwater for the sedum plants to use during drought conditions… sedums are drought tolerant plants, but they're not drought proof. If your roof slope is greater than 10 degrees, you may need to install an irrigation system too.
Water retention matting is also very useful in the greenhouse - stand pots on a layer of water retention matting to help cut down on watering.
Sedum matting
The all important vegetative layer. For more about Enviromat sedum matting, click here.
Wind uplift protection
Each piece of sedum matting has a flap of "spare" backing fabric tucked underneath it. When installing your Enviromat, unfold the flap and lay the next Enviromat slab on top of it to help protect against wind uplift. Edges should be secured using either paving slabs or 300mm of 20-30mm pebbles. Click here for more information about preventing wind uplift.
Detailing
For diagrams showing detailing around drainage outlets and for abutments, please click here.