A green roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage and irrigation systems.
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.
There are two types of green roofs: intensive roofs, which are thicker and can support a wider variety of plants but are heavier and require more maintenance,and extensive roofs, which are covered in a light layer of vegetation and are lighter than an intensive green roof.
Another important distinction is between pitched green roofs and flat green roofs. Pitched sod roofs, a traditional feature of many Scandinavian buildings,tend to be of a simpler design than flat green roofs. This is because the pitch of the roof reduces the risk of water penetrating through the roof structure, allowing the use of fewer waterproofing and drainage layers.
The term green roof may also be used to indicate roofs that use some form of "green" technology, such as a roof with solar thermal collectors or photovoltaic cells.
Container gardens on roofs, where plants are maintained in pots, are not generally considered to be true green roofs. Rooftop ponds are another form of green roofs which are used to treat greywater.
There are many potential benefits associated with green roofs. These include:
• Controlling storm water runoff
• Improving water quality
• Mitigating urban heat-island effects
• Prolonging the service life of roofing materials
• Conserving energy
• Reducing sound reflection and transmission
• Creating wildlife habitat, and
• Improving the aesthetic environment in both work and home settings.
