Green Roof Benefits
Reduction of Urban Heat Island – Research for climate change suggests we need a 10% increase in green space in our cities to combat climate change. This is particularly relevant to the reduction in the Urban Heat Island [UHIE]. Green roofs are recognized to have a positive effect on reducing the UHIE
Biodiversity - Green roofs can provide important refuges for wildlife in urban areas. Research in Switzerland and the UK has demonstrated that green roofs can provide important refuges for rare invertebrate populations.
Water - Green roofs can significantly reduce the surface run off volumes and rates of rainfall leaving roofs. As a source control mechanism in the Sustainable Urban Drainage System green roofs can help reduce flash floods as a consequence of intense rainfall events. This will become increasingly important as a consequence of climate change.
Green roofs also improve the quality of water and although the amount of water is reduced it is possible to rainfall harvest from roofs that have been greened.
Thermal Performance - Green roofs cannot be given a U-value at present. However they have been shown to significantly reduce the need for air conditioning in summer and can provide a degree of insulation in winter.
Sound Insulation - The combination of soil, plants and trapped layers of air within green roof systems can act as a sound insulation barrier. Sound waves are absorbed, reflected or deflected. The growing medium tends to block lower sound frequencies whilst the plants block higher frequencies.
Protection of Waterproofing - The original green roofs in Germany stem from covering wet bitumen with 6cm of sand, which became vegetated. This covering was to protect the wet bitumen from fire. Green roofs have now been shown to double if not triple the life of waterproofing membranes beneath the green roof.
Air Quality – airborne particles and pollutants are filtered from the atmosphere by the substrates and vegetation on a green roof.
Amenity Space – in dense urban environments there is often a lack of green space for residents. Roof Gardens and roof top parks provide important green spaces to improve the quality of life for urban residents.
Urban Agriculture - Urban Rooftop Food Growing – roofs, where strong enough provide a space for urban food growing. Although many large flat roofs may not have the loading capabilities to hold food growing some roofs will and the many balconies in are urban areas are ideal.
Intensive Green Roofs
Intensive Green Roofs Intensive green roofs have a deep growing medium, which allows the use of trees and shrubs. Some city parks are in fact intensive green roofs, such as the parks within the Canary Wharf Estate, Canada Square and West Ferry Circus and the roof of Cannon Street Station in London.
intensive green roofs require extra loading requirements The depth of the growing medium requires extra loading requirements within the holding structure and requires a complex irrigation system for maintenance. They are generally quite costly and require extra structural design to the building
Extensive Green Roofs
Extensive green roofs have a thin growing medium and require minimal maintenance, and in general due not require irrigation [some require irrigation initially]. They are generally less costly to install than intensive green roofs.
There are 3 types currently used in the UK:
1. Sedum mats
Sedum Mats - a sedum mat is a base layer of Polyester, Hessian, or porous polythene depending on the supplier, on which is laid the 2cm growing medium, on to which is sprinkled sedum cuttings. These grow into the substrate to maturity. When harvested the Sedum blanket is rolled up from the carrier upwards and delivered to site. When installed the Sedum blanket (including the 2cm of growing medium) is rolled out onto either 5 - 7cm of growing medium (standard method) or direct onto a moisture retention blanket (ultra light weight method).
Sedums are used because they are wind, frost and drought resistant not because they absorb water. Its ability to absorb water makes it drought resistant.
2. Substrate based roof
7cm of crushed recycled brick is placed on the green roof system and plug planted with sedums or with sedum mats applied. There is a misconception that green roofs are made of turf. Although some green roofs are made of turf this is not generally the case.
3. Brown roofs for biodiversity
See our page (Brown Roofs)