In addition to the beautiful appearance, a green roof also has many other benefits:
- it retains rainwater, preventing stormwater from overloading the sewer systems
- it protects the roof structures and extends the roof’s service life
- it keeps the room warm in the winter and cool in the summer: the temperature of a low-slope green roof may be up to 40 oC lower in the summer than that of a traditional black roof
- it dampens noise
- it improves the air quality by acting as a carbon sink as the plants turn carbon dioxide into oxygen.
It is important to have the architect, structural engineer, landscape designer and waterproofing supplier to design the green roof in cooperation.
High-quality waterproofing and root barrier protection form the basis for all green roof designs. Waterproofing is mainly implemented by torch-applied bitumen membranes and planned with particular consideration to the risks caused by the roots. Installation should be left to an experienced and professional contractor. A poorly constructed green roof may lead to expensive repairs because the leak point can be very difficult to find.
Structural solutions must take into account the snow and wind loads on the roof. If there are living spaces on the roof, safety must be ensured by, for example, appropriate railing. The design must also consider maintenance safety by, for example, providing appropriate access routes on the roof.
In the case of lightweight green roofs, the lifting effect of the wind must also be considered. Though wind rarely lifts green roofs, strong winds may affect a newly installed, unrooted sedum blanket at the perimeter or corners of the roof. This can be prevented by having a 500 mm wide pebble strip on the roof edges, overlaid on top of the vegetation by approximately 250 mm.
The most suitable slope for green roofs is 1:20…1:50, providing the best conditions for plants and preventing excessive moisture and drought. Flatter roofs (1:50…1:80) may be considered with reservations and taking into account the importance of drainage, for example. Anti-slip measures must be considered on slopes steeper than 1:5, and slopes steeper than 1:3 must be designed case-specifically with special anti-slip measures. Green roofs are not recommended for slopes steeper than 1:1.
Slopes and drainage should be designed to allow for unobstructed drainage of water from the roof. The roof drains should be equipped with electric resistors and surrounded by a 500 mm wide roof pebble strip. Roof pebble is used to prevent the substrate and roots from blocking the roof drains.