Green roof, an increasingly popular feature in sustainable buildings, is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. Green roof helps absorb rainwater and insulate the building. There could be several benefits of having green roof such as absorbing rainwater, providing insulation, lowering urban air temperatures and mitigate the heat island effect. Green roofs come in many different forms and types, usually a distinction is made between extensive, intensive and bio-diverse or wildlife roofs.
Intensive green roofs are generally heavy and require specific support from the building. Therefore intensive green roofs support a wide range of plant types: trees and shrubs as well as perennials, grasses and annuals. They are composed of relatively deep substrates (20cm+).
Recently, the extensive green roofs have received the greatest interest because they are composed of lightweight layers of free-draining material that support low-growing, hardy, drought-tolerant vegetation. The depth of growing medium for extensive green roofs is from a few centimetres up to a maximum of around 10-15cm. Further more , extensive green roofs require little in the way of maintenance and resource inputs. Also, they can be designed into new buildings, or ‘retro-fitted’ onto existing buildings.
Environmental Benefits of Green Roofs
Green roof reduces heating because of mass and thermal resistance value it adds to the roof of the building. According to a study, green roofs can also reduce heat loss and energy consumption in winter conditions. Green roofs not only retain rainwater, but also moderate the temperature of the water and act as natural filters for any of the water that happens to run off.
A concentration of green roofs in an urban area can even reduce the city's average temperatures during the summer! If installed correctly, the green roofs can contribute to LEED points. The water is stored by the substrate of green roof and then taken up by the plants from where it is returned back to the atmosphere through transpiration and evaporation.
Other Benefits of Green Roofs
Apart from environmental benefits, green roofs also have many social and economic benefits:
- Reducing storm-water runoff as part of a sustainable drainage systems (SuDS) strategy
- Increases roof lifespan
- Lowers energy use
- Climate change mitigation and adaptation
- Lessening the Urban Heat Island Effect (UHIE)
- Reduced sound transfer
- Improving air and water quality
- Increasing biodiversity and wildlife
