Green Roof

A green roof is a roof (http://en.wikipedia.org/wiki/Roof) of a building (http://en.wikipedia.org/wiki/Building) that is partially or completely covered with vegetation and soil, or a growing medium, planted over a waterproofing membrane. This does not refer to roofs which are merely colored green, as with green shingles. 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 an area of debate. The term "green roof" may also be used to indicate roofs that utilize some form of "green" technology, such as solar panels (http://en.wikipedia.org/wiki/Solar_panels) or a photovoltaic module (http://en.wikipedia.org/wiki/Photovoltaic_module). Green roofs are also referred to as eco-roofs, vegetated roofs, living roofs, and greenroofs.

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Benefits of green roofs

Green roofs are used to:

• Provide amenity space for building users — in effect replacing a yard (http://en.wikipedia.org/wiki/Yard_%28land%29) or patio (http://en.wikipedia.org/wiki/Patio)
• Grow fruits, vegetables, and flowers
• Reduce heating (http://en.wikipedia.org/wiki/HVAC) (by adding mass (http://en.wikipedia.org/wiki/Mass) and thermal resistance value) and cooling (by evaporative cooling (http://en.wikipedia.org/wiki/Evaporative_cooling)) loads on a building — especially if it is glassed in so as to act as a terrarium (http://en.wikipedia.org/wiki/Terrarium) and passive solar heat reservoir
• Reduce the urban heat island effect (http://en.wikipedia.org/wiki/Urban_heat_island_effect)
• Increase roof life span
• Reduce stormwater (http://en.wikipedia.org/wiki/Stormwater) run off — see water-wise gardening (http://en.wikipedia.org/wiki/Water-wise_gardening)
• Filter pollutants (http://en.wikipedia.org/wiki/Pollutant) and CO2 (http://en.wikipedia.org/wiki/CO2) out of the air — see living wall (http://en.wikipedia.org/wiki/Living_wall)
• Filter pollutants and heavy metals out of rainwater
• Increase wildlife habitat in built-up areas — see urban wilderness (http://en.wikipedia.org/wiki/Urban_wilderness)

A green roof is often a key component of an autonomous building (http://en.wikipedia.org/wiki/Autonomous_building).

According to Green Roofs for Healthy Cities (a network of public and private interests founded by Steven W. Peck (http://en.wikipedia.org/w/index.php?title=Steven_W._Peck&action=edit) based in Toronto (http://en.wikipedia.org/wiki/Toronto%2C_Canada)):

"In North America, the benefits of green roof technologies are poorly understood and the market remains immature, despite the efforts of several industry leaders. In Europe however, these technologies have become very well established."

A 2005 study by Brad Bass of the University of Toronto (http://en.wikipedia.org/wiki/University_of_Toronto) showed that green roofs can also reduce heat loss and energy consumption in winter conditions.[1 (http://www.news.utoronto.ca/bin6/051117-1822.asp)]

History and uses of green roofs

Modern green roofs, which are made of a system of manufactured layers deliberately placed over roofs to support growing medium and vegetation, are a relatively new phenomenon. They were developed in Germany in the 1960s, and have since spread to many countries. Today, it is estimated that about 10% of all German roofs have been “greened.” [2 (http://hortweb.cas.psu.edu/research/greenroofcenter/history.html)] Green roofs are also becoming increasingly popular in the United States, although they are not as common as in Europe.

Many green roofs are installed to comply with local regulations and government fees, often regarding stormwater runoff management.^{[1 (http://en.wikipedia.org/wiki/Green_roof#_note-0)]} 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. [3 (http://www.epa.gov/heatisland/strategies/greenroofs.html)] Elevation 314, a new development in Washington D.C., uses green roofs to filter and store some of its stormwater on site, avoiding the need for expensive underground sand filters to meet D.C. Department of Health stormwater regulations.

Combating the urban heat island effect [4 (http://science.nasa.gov/headlines/y2000/essd16mar_1m.htm)] is another reason for creating a green roof. Traditional building materials soak up the sun's radiation and reflect it back as heat, making cities at least 7 degrees hotter than surrounding areas. [5 (http://www.charityguide.org/volunteer/fewhours/green-roof.htm)] On Chicago's City Hall, by contrast, which features a green roof, temperatures on a hot day are typically 25–80 degrees Fahrenheit (14–44 degrees Celsius) cooler than they are on traditionally roofed buildings nearby. [6 (http://news.nationalgeographic.com/news/2002/11/1115_021115_GreenRoofs_2.html)]

Green roofs are becoming common in Chicago, as well as Atlanta, Portland, and other cities, where their use is encouraged by regulations to combat the urban heat island effect. 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 12 degrees Fahrenheit. [7 (http://msnbc.msn.com/id/6002705/site/newsweek/)]

Green roofs have also been found to dramatically improve a roof’s insulation value. A study conducted by Environment Canada found a 26% reduction in summer cooling needs and a 26% reduction in winter heat losses when a green roof is used. [8 (http://www.greenroofs.net/index.php?option=com_content&task=view&id=26&Itemid=40)] In addition, greening a roof is expected to lengthen a roof’s lifespan by two or three times, according to Penn State University’s Green Roof Research Center. [9 (http://hortweb.cas.psu.edu/research/greenroofcenter/history.html)]

Finally, green roofs provide habitat 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. [10 (http://www.charityguide.org/volunteer/fewhours/green-roof.htm)]

Types of green roof

Green roofs can be categorised as "intensive", "semi-intensive" or "extensive", depending on the depth of planting medium and the amount of maintenance they need. Traditional roof gardens (http://en.wikipedia.org/wiki/Roof_garden), which require a reasonable depth of soil to grow large plants or conventional lawns, are labour-intensive, requiring irrigation, feeding and other maintenance. "Extensive" green roofs, by contrast, are designed to be virtually self-sustaining and should only require a minimum of maintenance, perhaps a once-yearly weeding or an application of slow-release fertiliser to boost growth. They can be established on a very thin layer of "soil" (most use specially formulated composts): even a thin layer of rockwool (http://en.wikipedia.org/wiki/Rockwool) laid directly onto a watertight roof can support a planting of Sedum species and mosses.

Another important distinction is between pitched green roofs and flat green roofs. Pitched green 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.

(http://en.wikipedia.org/wiki/Image:Green_City.jpg)

Brown roofs

sites can be valuable ecosystems, supporting rare species of plants, animals and invertebrates. Increasingly in demand for redevelopment, these habitats are under threat. "Brown roofs" can partly mitigate this loss of habitat by covering the flat roofs of new developments with a thin layer of crushed rubble and gravel, ideally obtained at minimal cost from the redevelopment site itself. They are intended to be gradually colonised by spiders and insects and provide a feeding site for insectivorous birds. Laban (http://en.wikipedia.org/wiki/Laban_Dance_Centre), a centre for contemporary dance in London (http://en.wikipedia.org/wiki/London), has a brown roof specifically designed to encourage the locally rare Black Redstart (http://en.wikipedia.org/wiki/Black_Redstart). (In 2003 Laban won the coveted RIBA (http://en.wikipedia.org/wiki/RIBA) Stirling Prize (http://en.wikipedia.org/wiki/Stirling_Prize).) There are similar brown roofs on several nearby buildings in Deptford (http://en.wikipedia.org/wiki/Deptford), including the Creekside Education Centre.

Examples of green roofs

(http://en.wikipedia.org/wiki/Image:Green_Roof_at_Vend%C3%A9e_Historial%2C_les_Lucs.jpg)

(http://en.wikipedia.org/wiki/Image:Green_Roof_at_Vend%C3%A9e_Historial%2C_les_Lucs.jpg)

Green roof planted with native species at L'Historial de la Vendée, a new museum in western France (http://en.wikipedia.org/wiki/France)

One of the largest expanses of extensive green roof is to be found in the USA (http://en.wikipedia.org/wiki/USA), at Ford Motor Company (http://en.wikipedia.org/wiki/Ford_Motor_Company)'s River Rouge Plant (http://en.wikipedia.org/wiki/River_Rouge_Plant), Dearborn (http://en.wikipedia.org/wiki/Dearborn), Michigan (http://en.wikipedia.org/wiki/Michigan), where 42,000 square metres (454,000 ft²) of assembly plant roofs are covered with sedum (http://en.wikipedia.org/wiki/Sedum) and other plants. Other well-known American examples include Chicago’s City Hall and the Gap headquarters in San Bruno, Calif. The cities of Chicago, Atlanta and Portland, Ore., also boast numerous green roofs.[11 (http://www.charityguide.org/volunteer/fewhours/green-roof.htm)]

Switzerland has one of Europe's oldest green roofs, created in 1914 at the Moos lake water-treatment plant, Wallishofen (http://en.wikipedia.org/w/index.php?title=Wallishofen&action=edit), Zürich (http://en.wikipedia.org/wiki/Z%C3%BCrich). Its filter-tanks have 30,000 square metres (320,000 ft²) of flat concrete roofs. To keep the interior cool and prevent bacterial growth in the filtration beds, a drainage layer of gravel and a 15 cm (6 in) layer of soil was spread over the roofs, which had been waterproofed with asphalt (http://en.wikipedia.org/wiki/Asphalt). A meadow developed from seeds already present in the soil; it is now a haven for many plant species, some of which are now otherwise extinct in the district, most notably 6,000 Orchis morio (green-winged orchid (http://en.wikipedia.org/wiki/Green-winged_Orchid)). More recent Swiss examples can be found at Klinikum 1 and Klinikum 2, the Cantonal (http://en.wikipedia.org/wiki/Cantons_of_Switzerland) Hospitals of Basel (http://en.wikipedia.org/wiki/Basel), and the Sihlpost (http://en.wikipedia.org/w/index.php?title=Sihlpost&action=edit) platform at Zürich's main railway station.

What is believed to be the world's first green roof botanic garden (http://en.wikipedia.org/wiki/Botanic_garden) was set up in Augustenborg (http://en.wikipedia.org/wiki/Augustenborg), a suburb of Malmö (http://en.wikipedia.org/wiki/Malm%C3%B6), in May 1999. The International Green Roof Institute (IGRI) opened to the public in April 2001 as a research station and educational facility. (It has since been renamed the Scandinavian Green Roof Institute (SGRI), in view of the increasing number of similar organisations around the world.) Green roofs are well-established in Malmö: the Augustenborg housing development near the IGRI botanic garden incorporates green roofs and extensive imaginative landscaping of streams, ponds and soakaways between the buildings to deal with storm water run-off. The new Bo01 (http://en.wikipedia.org/w/index.php?title=Bo01&action=edit) urban residential development (in the Västra Hamnen (http://en.wikipedia.org/w/index.php?title=V%C3%A4stra_Hamnen&action=edit) (Western Harbour) close to the foot of the iconic Turning Torso (http://en.wikipedia.org/wiki/Turning_Torso) office and apartment block, designed by Santiago Calatrava (http://en.wikipedia.org/wiki/Santiago_Calatrava)) is built on the site of old shipyards and industrial areas, and incorporates many green roofs.

British examples can be found at the University of Nottingham (http://en.wikipedia.org/wiki/University_of_Nottingham) Library, and in London at the Horniman Museum (http://en.wikipedia.org/wiki/Horniman_Museum) and Canary Wharf (http://en.wikipedia.org/wiki/Canary_Wharf). The Ethelred Estate, close to the River Thames (http://en.wikipedia.org/wiki/Thames) in central London, is the British capital's largest roof-greening project to date. Toxteth (http://en.wikipedia.org/wiki/Toxteth) in Liverpool (http://en.wikipedia.org/wiki/Liverpool) is also a candidate for a major roof-greening project.

In France, a huge green roof of roughly 8,000 m² (70,000 ft²) has been incorporated into the new museum L'Historial de la Vendée (http://en.wikipedia.org/w/index.php?title=L%27Historial_de_la_Vend%C3%A9e&action=edit) which opened in June 2006 at Les Lucs-sur-Boulogne (http://en.wikipedia.org/w/index.php?title=Les_Lucs-sur-Boulogne&action=edit).