A Green roof also known as eco-roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. EPDM Rubber is widely used as the waterproof membrane for green roof construction because of its waterproofing properties and resilience. Green roofs serve several purposes for a building, such as absorbing rainwater, providing insulation, creating a habitat for wildlife, and helping to lower urban air temperatures and combat the heat island effect.
It is important to ensure before starting any green roof or roof garden project that the structure of the roof is sufficient to take the extra weight. The structural calculations need to account for the soil and also retained water that will be present in the soil. The roof should ideally have a fall towards any gutters of 1:50 or 20mm fall in every metre. A slight incline can be added to any flat roofs by installing wedged fillets to the existing joists and re-boarding.
The roof will require up-stands around the perimeter to contain the drainage, geotextile, soil and plants. This should be constructed from tanalised timber to prevent rot. A smaller up-stand will also be required at the drip edge or gutter edge of approximately 10-20mm to allow drainage.
Green Roof Installation
After ensuring that the roof structure is sound and structurally strong enough:
- Fit the frame used to retain the green roof components
- Install the EPDM roof membrane as described in our training section
- Lay a sheet of geotextile fleece over the EPDM to protect the membrane and retain moisture
- Install a drainage layer using either rounded washed pebbles (Not Pea Gravel) or profiled troughs to help drainage and retain sufficient moisture
- Fit another geotextile membrane or similar rot resistant hi tensile membrane to retain soil and to avoid drainage layer silting up
- Add the soil layer. Depth is dependant on choice of plants and root depth requirements
- Plant up the area with your choice of species. It is important to consider the plants growth rate, need for maintenance, water requirements and position of the roof in relation to the sun