|Saint Mary's University research green roof|
There are two types of green roofs - intensive and extensive. Intensive green roofs have deep soils which can support a wide variety of plant species, including larger shrubs and trees. They are used for both aesthetic and functional purposes. Intensive roofs require maintenance and care, much like a typical home garden. Extensive green roofs use less soil (layer can range between 2 - 20cm) which makes them much lighter, but also limits the variety of plants that can be grown in such shallow conditions. Grasses, mosses and sedum species are commonly used. Extensive green roofs require little to no maintenance. Some roofs may need irrigation for the first year while the plants are establishing, but they can then be left entirely on their own.
Green roofs can be installed in three ways. Soil can be brought to the roof top and placed on top of the required waterproofing, filtering and insulation layers then planted with selected vegetation. More typically, green roofs are installed as small modules or vegetation trays that contain soil, plants and a shallow gravel layer to ensure the contents are secure on windy rooftop conditions. A third option, known as pre-cultivated vegetation blankets, are composed of soil and vegetation mats that can simply be rolled out onto the rooftop.
|Green roof modules|
|Green roof layers including pre-cultivated vegetation blanket (www.xeroflor.ca)|
The city of Toronto has introduced a Green Roof Bylaw that requires the construction of green roofs on all new buildings of a certain size. You can read more about Toronto's bylaw here.