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A green roof or living 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. Container gardens on roofs, where plants are maintained in pots, are not generally considered to be true green roofs, although this is debated. Rooftop ponds are another form of green roofs which are used to treat greywater. Green roofs serve several purposes for a building, such as absorbing rainwater, providing insulation, creating a habitat for wildlife, increasing benevolence and decreasing stress of the people around the roof by providing a more aesthetically pleasing landscape, and helping to lower urban air temperatures and mitigate the heat island effect. They effectively utilize the natural functions of plants to filter water and treat air in urban and suburban landscapes.〔https://sftool.gov/explore/green-building/section/76/green-roof/system-overview#green-roof/extensive-green-roofs〕 There are two types of green roof: intensive roofs, which are thicker, with a minimum depth of , and can support a wider variety of plants but are heavier and require more maintenance, and extensive roofs, which are shallow, ranging in depth from to , lighter than intensive green roofs, and require minimal maintenance. The term ''green roof'' may also be used to indicate roofs that use some form of green technology, such as a cool roof, a roof with solar thermal collectors or photovoltaic panels. Green roofs are also referred to as ''eco-roofs'', ''oikosteges'', ''vegetated roofs'', ''living roofs'', ''greenroofs'' and ''VCPH〔Vegetated Complex Partition research presentation on (Aurélien P. JEAN ) research website〕 (Horizontal Vegetated Complex Partitions). ==Environmental benefits== Green roofs are used to: *Reduce heating (by adding mass and thermal resistance value) A 2005 study by Brad Bass of the University of Toronto showed that green roofs can also reduce heat loss and energy consumption in winter conditions. *Reduce cooling (by evaporative cooling) loads on a building by fifty to ninety percent,〔Living Roofs designer http://www.roofgreening.ca/living_roofs.php〕 especially if it is glassed in so as to act as a terrarium and passive solar heat reservoir – a concentration of green roofs in an urban area can even reduce the city's average temperatures during the summer *Reduce stormwater run off〔http://www.roofgreening.ca/content/Improved_Final.pdf〕 — see water-wise gardening —A study presented at the Green Roofs for Healthy Cities Conference in June 2004, cited by the EPA, found water runoff was reduced by over 75% during rainstorms. See the PDF at 〔http://www.epa.gov/heatisland/resources/pdf/GreenRoofsCompendium.pdf〕 for more information. *Natural Habitat Creation〔http://www.roofgreening.ca/content/Habitat_Final.pdf〕 — see urban wilderness *Filter pollutants and carbon dioxide out of the air which helps lower disease rates such as asthma〔http://www.roofgreening.ca/content/AirQuality_Final.pdf〕— see green wall *Filter pollutants and heavy metals out of rainwater *Help to insulate a building for sound; the soil helps to block lower frequencies and the plants block higher frequencies〔Green Roofs for Healthy Cities: About Green Roofs. www.greenroofs.org〕 *If installed correctly many living roofs can contribute to LEED points *Increase agricultural space *With green roofs, water is stored by the substrate and then taken up by the plants from where it is returned to the atmosphere through transpiration and evaporation. *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. Many green roofs are installed to comply with local regulations and government fees, often regarding stormwater runoff management. In areas with combined sewer-stormwater systems, heavy storms can overload the wastewater system and cause it to flood, dumping raw sewage into the local waterways. Green roofs decrease the total amount of runoff and slow the rate of runoff from the roof. It has been found that they can retain up to 75% of rainwater, gradually releasing it back into the atmosphere via condensation and transpiration, while retaining pollutants in their soil.〔(【引用サイトリンク】Green Roofs – Heat Island Effect )〕 Often, phosphorus and nitrogen are in this category of environmentally harmful substances even though they are stimulating to the growth of plant life and agriculture. When these substances are added to a system, it can create mass biological activity since they are considered limiting factors of plant growth and by adding more of them to a system, it allows for more plant growth.(Elevation 314 ), a new development in Washington, D.C. uses green roofs to filter and store some of its storm water on site, avoiding the need for expensive underground sand filters to meet D.C. Department of Health storm-water regulations. Combating the urban heat island effect〔(【引用サイトリンク】Here Comes Urban Heat )〕 is another reason for creating a green roof. Traditional building materials soak up the sun's radiation and re-emit it as heat, making cities at least hotter than surrounding areas. On Chicago's City Hall, by contrast, which features a green roof, roof temperatures on a hot day are typically cooler than they are on traditionally roofed buildings nearby.〔(【引用サイトリンク】Plant-Covered Roofs Ease Urban Heat )〕 Green roofs are becoming common in Chicago, as well as in Atlanta, Portland, and other United States cities, where their use is encouraged by regulations to combat the urban heat-island effect. Green roofs are a type of low impact development.〔(【引用サイトリンク】Urban Waterways )〕 In the case of Chicago, the city has passed codes offering incentives to builders who put green roofs on their buildings. The Chicago City Hall green roof is one of the earliest and most well-known examples of green roofs in the United States; it was planted as an experiment to determine the effects a green roof would have on the microclimate of the roof. Following this and other studies, it has now been estimated that if all the roofs in a major city were greened, urban temperatures could be reduced by as much as 7 degrees Celsius. Green roofs also provide habitats for plants, insects, and animals that otherwise have limited natural space in cities. Even in high-rise urban settings as tall as 19 stories, it has been found that green roofs can attract beneficial insects, birds, bees and butterflies. Rooftop greenery complements wild areas by providing stepping stones for songbirds, migratory birds and other wildlife facing shortages of natural habitat. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「green roof」の詳細全文を読む スポンサード リンク
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