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{{Short description|Roof covered with vegetation}}
{{Use dmy dates|date=November 2020}}
[[File:British Horse Society Head Quarters and Green Roof.jpg|thumb|Green roof at the [[British Horse Society]] headquarters]]

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#Construction waterproofing|waterproofing membrane]]. It may also include additional layers such as a [[root barrier]] and [[drainage]], and [[irrigation]] systems.<ref name="multiple">{{cite thesis |id={{ProQuest|900864997}} |last1=Rodriguez Droguett |first1=Barbara |year=2011 |title=Sustainability assessment of green infrastructure practices for stormwater management: A comparative emergy analysis }}</ref> [[Container garden]]s on roofs, where plants are maintained in pots, are not generally considered to be true green roofs, although this is debated. Rooftop [[Pond|ponds]] are another form of green roofs, which are used to treat [[greywater]].<ref>Özyavuz, Murat, B. Karakaya, and D. G. Ertin. "The Effects of Green Roofs on Urban Ecosystems." GreenAge Symposium 2015.</ref> Vegetation, soil, drainage layer, roof barrier, and irrigation system constitute the green roof.<ref>EPA (2017) Green Roofs. U.S. EPA. Available from: [https://web.archive.org/web/20040831080058/http://www.epa.gov/heatisland/strategies/greenroofs.html]</ref>

Green roofs serve several purposes for a building, such as [[Absorption of water|absorbing]] [[rain]]water, providing [[Building insulation|insulation]], creating a habitat for [[wildlife]],<ref>{{Cite web|url=http://www.greenroof.hrt.msu.edu/benefits/index.html|title=Benefits of Green Roofs|website=www.greenroof.hrt.msu.edu|access-date=1 November 2018|archive-date=4 July 2018|archive-url=https://web.archive.org/web/20180704130158/http://www.greenroof.hrt.msu.edu/benefits/index.html}}</ref> 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]].<ref>{{cite journal |last1=Vandermeulen |first1=Valerie |last2=Verspecht |first2=Ann |last3=Vermeire |first3=Bert |last4=Van Huylenbroeck |first4=Guido |last5=Gellynck |first5=Xavier |title=The use of economic valuation to create public support for green infrastructure investments in urban areas |journal=Landscape and Urban Planning |date=November 2011 |volume=103 |issue=2 |pages=198–206 |doi=10.1016/j.landurbplan.2011.07.010 |bibcode=2011LUrbP.103..198V |url=https://biblio.ugent.be/publication/1955316/file/6762950 |url-access=subscription }}</ref> Green roofs are suitable for [[Retrofitting|retrofit]] or [[redevelopment]] projects as well as new buildings and can be installed on small garages or larger industrial, commercial and municipal buildings.<ref name="multiple" /> They effectively use the natural functions of plants to filter water and treat air in urban and suburban landscapes.<ref>{{cite web|url=https://sftool.gov/explore/green-building/section/76/green-roof/system-overview#green-roof/extensive-green-roofs|title=System Overview : Planted Roof: GSA Sustainable Facilities Tool|website=sftool.gov}}</ref> There are two types of green roof: intensive roofs, which are thicker, with a minimum depth of {{convert|12.8|cm|abbr=on|frac=16}}, 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 {{convert|2|to|12.7|cm|abbr=on|frac=16}}, lighter than intensive green roofs, and require minimal maintenance.<ref>{{cite journal |last1=Volder |first1=Astrid |last2=Dvorak |first2=Bruce |title=Event size, substrate water content and vegetation affect storm water retention efficiency of an un-irrigated extensive green roof system in Central Texas |journal=Sustainable Cities and Society |date=February 2014 |volume=10 |pages=59–64 |doi=10.1016/j.scs.2013.05.005 |bibcode=2014SusCS..10...59V }}</ref>

The term ''green roof'' may also be used to indicate roofs that use some form of [[Environmental technology|green technology]], such as a [[cool roof]], a roof with [[solar thermal collector]]s or [[photovoltaic panels]]. Green roofs are also referred to as ''eco-roofs'', ''oikosteges'', ''vegetated roofs'', ''living roofs'', ''greenroofs'' and ''VCP<sub>H</sub><ref name="VCP">{{cite web |url=http://personnel.univ-reunion.fr/ajean/typosite/index.html |title=Aurélien P. JEAN |access-date=19 May 2011 |archive-url=https://web.archive.org/web/20110824075700/http://personnel.univ-reunion.fr/ajean/typosite/index.html |archive-date=24 August 2011  }}</ref> (Horizontal Vegetated Complex Partitions)''

==Environmental benefits==
=== Thermal reduction and energy conservation ===
[[File:Construction sample of a green roof system.jpg|thumb|alt=Model of the components in a green roof system|Model of layers and components used in some green roof systems]]
Green roofs improve and reduce energy consumption.<ref>Li, W. (2013). A scenario planning approach for school green roofs to achieve stormwater management benefits: A case study of Brier's Mill Run Subwatershed</ref> They can reduce [[HVAC|heating]] by adding [[mass]] and thermal resistance value, and can reduce the heat island effect by increasing [[evapotranspiration]].<ref>Santamouris, M. (2014). Cooling the cities – A review of reflective and green roof mitigation technologies to fight heat island and improve comfort in urban environments. Solar Energy, 103(Supplement C), 682–703.</ref> 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.<ref>{{cite web
  |url = http://www.news.utoronto.ca/bin6/051117-1822.asp
  |title = University of Toronto – News@UofT – Green roofs in winter: Hot design for a cold climate
  |date=17 November 2005
  |access-date =10 June 2008
|archive-url = https://web.archive.org/web/20080411230309/http://www.news.utoronto.ca/bin6/051117-1822.asp <!-- Bot retrieved archive --> |archive-date = 11 April 2008}}</ref><ref>{{Cite journal |last1=Niachou |first1=A |last2=Papakonstantinou |first2=K |last3=Santamouris |first3=M |last4=Tsangrassoulis |first4=A |last5=Mihalakakou |first5=G |date=September 2001 |title=Analysis of the green roof thermal properties and investigation of its energy performance |journal=Energy and Buildings |volume=33 |issue=7 |pages=719–729 |doi=10.1016/s0378-7788(01)00062-7 |bibcode=2001EneBu..33..719N |issn=0378-7788}}</ref> A modeling study found that adding green roofs to 50 percent of the available surfaces in downtown Toronto would cool the entire city by {{convert|0.2|to|1.4|F-change|1|order=flip}}.<ref>Reducing Urban Heat Islands: Compendium of Strategies, Green Roofs. Available from:https://www.epa.gov/heatislands</ref>

Through [[evaporative cooling]], a green roof reduces cooling loads on a building by fifty to ninety percent,<ref>{{cite web |url=http://www.roofgreening.ca/living_roofs.php |title=Nedlaw Living Roofs - Living Roofs |access-date=5 February 2010 |archive-url=https://web.archive.org/web/20100105055802/http://www.roofgreening.ca/living_roofs.php |archive-date=5 January 2010  }}</ref> especially if it is glassed-in to act as a [[terrarium]] and [[passive solar building design|passive solar]] heat reservoir.

A concentration of green roofs in an urban area can reduce the city's average temperatures during the summer, combating the [[urban heat island effect]].<ref>{{cite web|url=https://science.nasa.gov/headlines/y2000/essd16mar_1m.htm|title=Here Comes Urban Heat|archive-url=https://web.archive.org/web/20080515014040/http://science.nasa.gov/headlines/y2000/essd16mar_1m.htm|archive-date=15 May 2008|access-date=10 June 2008}}</ref> Traditional building materials soak up the sun's [[solar radiation|radiation]] and re-emit it as heat, making cities at least {{convert|4|C-change}} hotter than surrounding areas. On Chicago's City Hall, by contrast, which features a green roof, roof temperatures on a hot day are typically {{convert|1.4|–|4.4|C-change}} cooler than they are on traditionally roofed buildings nearby.<ref>{{cite web|url=http://news.nationalgeographic.com/news/2002/11/1115_021115_GreenRoofs_2.html|archive-url=https://web.archive.org/web/20051230233828/http://news.nationalgeographic.com/news/2002/11/1115_021115_GreenRoofs_2.html|archive-date=30 December 2005|title=Plant-Covered Roofs Ease Urban Heat|access-date=10 June 2008}}</ref> 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 (UK)|low impact development]].<ref>{{cite web|url=http://www.bae.ncsu.edu/stormwater/PublicationFiles/BMPs4LID.pdf|title=Urban Waterways|archive-url=https://web.archive.org/web/20060719085522/http://www.bae.ncsu.edu/stormwater/PublicationFiles/BMPs4LID.pdf|archive-date=19 July 2006|access-date=14 June 2012}}</ref> 
A 2023 meta-analysis found that green roofs reduce rooftop surface temperatures by an average of 30 °C during summer months, providing significant mitigation of urban heat island effects.<ref>Wang, L., & Zhang, Y. (2023).</ref>
A 2023 systematic review of 86 studies reported that extensive green roofs typically reduce roof surface temperatures by 15–30 °C during peak summer conditions, while also lowering indoor temperatures by 1–4 °C depending on substrate depth and regional climate.<ref name="Li2023" />
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 {{convert|7|C-change}}.<ref>{{cite web|url=http://msnbc.msn.com/id/6002705/site/newsweek/|title=Is that a Garden on Your Roof? - Enterprise The Future of Energy - MSNBC.com|archive-url=https://web.archive.org/web/20070907051136/http://www.msnbc.msn.com/id/6002705/site/newsweek/ <!-- Bot retrieved archive -->|archive-date=7 September 2007|access-date=10 June 2008}}</ref>

=== Water management ===
[[File:Green roof bike rack.jpg|thumb|A green roof being used on a bike rack to keep bikes dry.]]
Green roofs can reduce [[stormwater]] runoff<ref>{{cite web |url=http://www.roofgreening.ca/content/Improved_Final.pdf |title=Archived copy |access-date=5 February 2010 |archive-url=https://web.archive.org/web/20110706202511/http://www.roofgreening.ca/content/Improved_Final.pdf |archive-date=6 July 2011  }}</ref><ref>{{Cite journal |last1=Shafique |first1=Muhammad |last2=Kim |first2=Reeho |last3=Kyung-Ho |first3=Kwon |date=March 2018 |title=Green Roof for Stormwater Management in a Highly Urbanized Area: The Case of Seoul, Korea |journal=Sustainability |language=en |volume=10 |issue=3 |page=584 |doi=10.3390/su10030584 |doi-access=free |bibcode=2018Sust...10..584S |issn=2071-1050}}</ref> via [[water-wise gardening]] techniques. Green roofs play a significant role in retrofitting the [[Low-impact development (U.S. and Canada)|Low Impact Development]] (LID) practices in urban areas.<ref>{{cite journal |last1=Shafique |first1=Muhammad |last2=Kim |first2=Reeho |title=Retrofitting the Low Impact Development Practices into Developed Urban areas Including Barriers and Potential Solution |journal=Open Geosciences |date=20 June 2017 |volume=9 |issue=1 |page=20 |doi=10.1515/geo-2017-0020 |bibcode=2017OGeo....9...20S |doi-access=free }}</ref> 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.<ref name=GreenRoofs/> Water is stored by the roof's substrate and then taken up by the plants, from which it is returned to the atmosphere through transpiration and evaporation.

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.<ref name=GreenRoofs>{{cite report|chapter-url=https://www.epa.gov/sites/production/files/2017-05/documents/reducing_urban_heat_islands_ch_3.pdf|chapter=Green Roofs|title=Reducing Urban Heat Islands: Compendium of Strategies|url=https://www.epa.gov/heatislands/guide-reducing-heat-islands|author=U.S. Environmental Protection Agency|date=2008|access-date=9 June 2017}}</ref> Many green roofs are installed to comply with local regulations and government fees, often regarding [[stormwater]] runoff management.<ref>{{cite book|title=Green Roofs: Ecological Design and Construction|author=Earth Pledge|publisher=Schiffer Pub.|year=2005|location=Atglen, PA}}</ref> In areas with [[combined sewer|combined sewer-stormwater systems]], heavy storms can [[sanitary sewer overflow|overload]] the [[water treatment|wastewater system]] and cause it to flood, dumping raw sewage into the local waterways. 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.<ref>{{cite book|url=https://www.ars.usda.gov/page-not-found/?aspxerrorpath=/is/np/Phos&Eutro2/agphoseutro2ed.pdf|title=Agricultural Phosphorus and Eutrophication|last=Sharpley|first=A.N.|date=September 2003}}</ref>

=== Ecological benefits ===
Green roofs create natural [[habitat]] as part of an [[urban wilderness]].<ref>{{cite web |url=http://www.roofgreening.ca/content/Habitat_Final.pdf |title=Archived copy |access-date=5 February 2010 |archive-url=https://web.archive.org/web/20110706202518/http://www.roofgreening.ca/content/Habitat_Final.pdf |archive-date=6 July 2011  }}</ref> 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. A recent list of the bee species recorded from green roofs (worldwide) highlights both the diversity of species, but also the (expected) bias towards small ground-nesting species (Hofmann and Renner, 2017). Rooftop greenery complements wild areas by providing stepping stones for songbirds, migratory birds, and other wildlife facing [[habitat destruction|shortages of natural habitat]]. Bats have also been reported to be more active over green roofs due to the foraging opportunities these roofs provide.<ref>{{Cite journal |last1=Partridge |first1=Dustin R. |last2=Parkins |first2=Kaitlyn L. |last3=Elbin |first3=Susan B. |last4=Clark |first4=J. Alan |date=2020-03-03 |title=Bat Activity Correlates with Moth Abundance on an Urban Green Roof |url=https://bioone.org/journals/northeastern-naturalist/volume-27/issue-1/045.027.0107/Bat-Activity-Correlates-with-Moth-Abundance-on-an-Urban-Green/10.1656/045.027.0107.full |journal=Northeastern Naturalist |volume=27 |issue=1 |page=77 |doi=10.1656/045.027.0107 |issn=1092-6194|url-access=subscription }}</ref> Research at the [[Javits Center]] green roof in New York, NY, has shown a correlation between higher numbers of certain insects on the roof, particularly moths, with an increased amount of bat foraging activity. Research from 2023 in St. Louis, Missouri, showed that urban rooftop food gardens support diverse bee populations, enhancing urban [[pollination]] and [[biodiversity]].<ref>{{Cite journal |last1=Riehn |first1=Jordyn K. |last2=Fogel |first2=Nina S. |last3=Hathaway |first3=Jordan N. |last4=Camilo |first4=Gerardo R. |date=2023-02-03 |title=Bee diversity on urban rooftop food gardens |journal=Frontiers in Sustainable Cities |volume=5 |doi=10.3389/frsc.2023.1100470 |doi-access=free |bibcode=2023FrSC....500470R |issn=2624-9634}}</ref>

Green roofs also serve as a [[green wall]], filtering [[pollutant]]s and [[carbon dioxide]] out of the air, helping to lower rates of diseases such as [[asthma]].<ref>{{cite web |url=http://www.roofgreening.ca/content/AirQuality_Final.pdf |title=Archived copy |access-date=5 February 2010 |archive-url=https://web.archive.org/web/20110706202524/http://www.roofgreening.ca/content/AirQuality_Final.pdf |archive-date=6 July 2011  }}</ref> They can also filter pollutants and [[heavy metals]] out of rainwater.

=== Carbon sequestration ===
An additional environmental benefit of a green roof is the ability to sequester carbon. [[Carbon]] is the main component of plant matter and is naturally absorbed by plant tissue. The carbon is stored in the plant tissue and the soil substrate through plant litter and root exudates.<ref name="Rowe 2100–2110">{{cite journal |last1=Rowe |first1=D. Bradley |title=Green roofs as a means of pollution abatement |journal=Environmental Pollution |date=August 2011 |volume=159 |issue=8–9 |pages=2100–2110 |doi=10.1016/j.envpol.2010.10.029 |pmid=21074914 |bibcode=2011EPoll.159.2100R |url=https://zenodo.org/record/1027905 }}</ref> A study on green roofs in Michigan and Maryland found the above-ground biomass and below ground substrate stored on average between 168 g C m<sup>−2</sup> and 107 g C m<sup>−2</sup> . Variations occurred among the different species of plant used.  Substrate carbon content averaged 913 g C m<sup>−2</sup> and after the subtraction of the original carbon content the total sequestration was 378 g C m<sup>−2</sup>.<ref name="Getter 7564–7570">{{cite journal |last1=Getter |first1=Kristin L. |last2=Rowe |first2=D. Bradley |last3=Robertson |first3=G. Philip |last4=Cregg |first4=Bert M. |last5=Andresen |first5=Jeffrey A. |title=Carbon Sequestration Potential of Extensive Green Roofs |journal=Environmental Science & Technology |date=October 2009 |volume=43 |issue=19 |pages=7564–7570 |doi=10.1021/es901539x |pmid=19848177 |bibcode=2009EnST...43.7564G }}</ref> The sequestration can be improved by changing plant species, increasing substrate depth, substrate composition, and management practices. In a study done in Michigan above ground sequestration ranged from 64 g C m<sup>−2</sup> to 239 g C m<sup>−2</sup> for S. acre and S album.<ref name="Getter 7564–7570" /> Also, by increasing the substrate depth would allow for more area of carbon storage and diversify the types of plants with greater potential of carbon storage. The direct [[carbon sequestration]] techniques and methods can be measured and accounted for. Green roofs also indirectly reduce CO<sub>2</sub> given off by power plants through their ability to insulate buildings.<ref name="Rowe 2100–2110" /> Buildings in the US account for 38% of the total carbon dioxide emissions.<ref>{{cite web|url=http://www.usgbc.org/articles/green-building-facts|title=Green Building Facts {{!}} U.S. Green Building Council|website=www.usgbc.org|access-date=29 February 2016}}</ref> A model supported by the U.S. Department of Energy found a 2 percent reduction in electricity consumption and 9-11% reduction in natural gas when implementing green roofs. Through this, a 2023 comprehensive review highlighted that green roofs also contribute to carbon dioxide reduction through both direct sequestration and indirect mechanisms, such as decreasing building energy consumption and mitigating urban heat islands.<ref>{{Cite journal |last=Tan |first=Taotao |last2=Kong |first2=Fanhua |last3=Yin |first3=Haiwei |last4=Cook |first4=Lauren M. |last5=Middel |first5=Ariane |last6=Yang |first6=Shaoqi |date=2023 |title=Carbon dioxide reduction from green roofs: A comprehensive review of processes, factors, and quantitative methods |url=https://ideas.repec.org/a/eee/rensus/v182y2023ics1364032123002691.html |journal=Renewable and Sustainable Energy Reviews |language=en |volume=182 |issue=C}}</ref>

=== Other ===
*Help to insulate a building for sound; the soil helps to block lower frequencies and the plants block higher frequencies<ref>{{cite web|url=http://www.greenroofs.org |title=Green Roofs for Healthy Cities |website=Greenroofs.org |access-date=23 June 2017}}</ref>
*If installed correctly many living roofs can contribute to [[Leadership in Energy and Environmental Design|LEED]] points
*Increase agricultural space
*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.

==Costs and financial benefits==
[[File: Rooftop farm at the Essex (65787p).jpg|thumb|[[Roof garden]] which highlights a roof that uses [[Raised-bed gardening|garden boxes]] which can be a more economical solution for a green roof]]

A properly designed and installed extensive green-roof system can cost {{convert|108|-|248|$/m2|$/ft2|0|abbr=on}} while an intensive green roof costs {{convert|355|-|2368|$/m2|$/ft2|0|abbr=on}} However, since most of the materials used to build the green roof can be salvaged, it is estimated that the cost of replacing a green roof is generally one third of the initial installation costs.<ref>{{cite journal |last1=Sproul |first1=Julian |last2=Wan |first2=Man Pun |last3=Mandel |first3=Benjamin H. |last4=Rosenfeld |first4=Arthur H. |title=Economic comparison of white, green, and black flat roofs in the United States |journal=Energy and Buildings |date=March 2014 |volume=71 |pages=20–27 |doi=10.1016/j.enbuild.2013.11.058 |bibcode=2014EneBu..71...20S |url=https://zenodo.org/record/1258915 }}</ref>

With the initial cost of installing a green roof in mind, there are many financial benefits that accompany green roofing.
*Green roofing can extend the lifespan of a roof by over 200% by covering the waterproofing membrane with growing medium and vegetation, this shields the membrane from ultra-violet radiation and physical damage.<ref>{{cite journal |last1=Carter |first1=Timothy |last2=Keeler |first2=Andrew |title=Life-cycle cost–benefit analysis of extensive vegetated roof systems |journal=Journal of Environmental Management |date=May 2008 |volume=87 |issue=3 |pages=350–363 |doi=10.1016/j.jenvman.2007.01.024 |pmid=17368704 |bibcode=2008JEnvM..87..350C }}</ref> Further, Penn State University's Green Roof Research Center expects the lifespan of a roof to increase by as much as three times after [[greening]] the roof.<ref name="hortweb1" />
*It is estimated that the installation of a green roof could increase the [[real estate]] value of an average house by about 7%.<ref>{{cite journal |last1=Bianchini |first1=Fabricio |last2=Hewage |first2=Kasun |title=Probabilistic social cost-benefit analysis for green roofs: A lifecycle approach |journal=Building and Environment |date=December 2012 |volume=58 |pages=152–162 |doi=10.1016/j.buildenv.2012.07.005 |bibcode=2012BuEnv..58..152B }}</ref>
*Reduction in energy use is an important property of green roofing.  By improving the thermal performance of a roof, green roofing allows buildings to better retain their heat during the cooler winter months while reflecting and absorbing solar radiation during the hotter summer months, allowing buildings to remain cooler.  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.<ref>{{cite web |url=http://www.greenroofs.net/index.php?option=com_content&task=view&id=26&Itemid=40 |title=Green Roofs for Healthy Cities - About Green Roofs |access-date=10 June 2008 |archive-url=https://web.archive.org/web/20080502015516/http://www.greenroofs.net/index.php?option=com_content&task=view&id=26&Itemid=40 |archive-date=2 May 2008  }}</ref> With respect to hotter summer weather, green roofing is able to reduce the solar heating of a building by reflecting 27% of solar radiation, absorbing 60% by the vegetation through photosynthesis and evapotranspiration, and absorbing the remaining 13% into the growing medium. Such mitigation of solar radiation has been found to reduce building temperatures by up to {{convert|20|C-change}} and reduce energy needs for air-conditioning by 25% to 80%.  This reduction in energy required to cool a building in the summer is accompanied by a reduction in energy required to heat a building in the winter, thus reducing the energy requirements of the building year-round which allows the building temperature to be controlled at a lower cost.<ref name="Saadatian et al 2013"/>
*Depending on the region in which a green roof is installed, incentives may be available in the form of stormwater tax reduction, grants, or rebates.  The regions where these incentives will most likely be found are areas where failing storm water management infrastructure is in place, urban heat island effect has significantly increased the local air temperature, or areas where environmental contaminants in the storm water runoff is of great concern.<ref>{{cite journal |last1=VanWoert |first1=Nicholaus D. |last2=Rowe |first2=D. Bradley |last3=Andresen |first3=Jeffrey A. |last4=Rugh |first4=Clayton L. |last5=Fernandez |first5=R. Thomas |last6=Xiao |first6=Lan |title=Green Roof Stormwater Retention: Effects of Roof Surface, Slope, and Media Depth |journal=Journal of Environmental Quality |date=May 2005 |volume=34 |issue=3 |pages=1036–1044 |doi=10.2134/jeq2004.0364 |pmid=15888889 }}</ref> An example of such an incentive is a one-year property tax credit is available in [[New York City]], since 2009, for property owners who green at least 50% of their roof area.<ref name="EL NYC">[http://www.environmentalleader.com/2008/06/29/tax-credits-for-green-rooftops-in-nyc/ 'Tax Credits For Green Rooftops In NYC'], Environmental Leader, 29 June 2008. Retrieved 10 July 2012.</ref>

==Disadvantages==
[[File:City University of Hong Kong Hu Fa Kuang Sports Centre roof collapses site on 21st May 2016.jpg|thumb|The addition of a green roof to an existing structure led to this collapse at the [[City University of Hong Kong]].]]

The main disadvantage of green roofs is that the initial cost of installing a green roof can be double that of a normal roof.<ref>{{cite journal |last1=Getter |first1=Kristin L. |last2=Rowe |first2=D. Bradley |title=The Role of Extensive Green Roofs in Sustainable Development |journal=HortScience |date=August 2006 |volume=41 |issue=5 |pages=1276–1285 |doi=10.21273/HORTSCI.41.5.1276 |doi-access=free }}</ref> Depending on what kind of green roof it is, the maintenance costs could be higher, but some types of green roof have little or no ongoing cost. Some kinds of green roofs also place higher demands on the [[waterproofing]] system of the structure, both because water is retained on the roof and due to the possibility of roots penetrating the waterproof membrane. Another disadvantage is that the wildlife they attract may include [[Pest (organism)|pest]] insects which could easily infiltrate a residential building through open windows.

The additional mass of the soil substrate and retained water places a large strain on the structural support of a building.  This makes it unlikely for intensive green roofs to become widely implemented due to a lack of buildings that are able to support such a large amount of added weight as well as the added cost of reinforcing buildings to be able to support such weight.<ref>{{cite journal |last1=Currie |first1=Beth Anne |last2=Bass |first2=Brad |title=Estimates of air pollution mitigation with green plants and green roofs using the UFORE model |journal=Urban Ecosystems |date=December 2008 |volume=11 |issue=4 |pages=409–422 |doi=10.1007/s11252-008-0054-y |bibcode=2008UrbEc..11..409C |s2cid=22157617 }}</ref> Some types of green roofs do have more demanding structural standards especially in seismic regions of the world.  Some existing buildings cannot be retrofitted with certain kinds of green roofs because of the weight load of the substrate and vegetation exceeds permitted [[static load]]ing. The weight of a green roof caused the collapse of a large sports hall roof in Hong Kong in 2016.<ref>{{cite news|last1=Cheng|first1=Kris|last2=Cheung|first2=Karen|title=Roof collapses at City University sports centre, three injured|url=https://www.hongkongfp.com/2016/05/20/breaking-roof-collapses-at-cityu-at-least-three-injured/|work=[[Hong Kong Free Press]]|date=20 May 2016}}</ref> In the wake of the disaster, numerous other green roofs around the territory were removed.<ref>{{cite news|last1=Tsang|first1=Emily|title=Chinese University of Hong Kong to remove green roofs, Buildings Department issues new guidelines for immediate safety checks|url=https://www.scmp.com/news/hong-kong/health-environment/article/1952707/chinese-university-hong-kong-remove-green-roofs|work=South China Morning Post|date=24 May 2015}}</ref>

Green roofs require significantly more maintenance and maintenance energy compared to a standard roof. Standard maintenance includes removing debris, controlling weeds, deadheading, trimming, checking moisture levels, and fertilizing.<ref>{{cite web
| url = http://columbia-green.com/wp-content/uploads/2014/08/CGT_Maintenance_July2014.pdf
| title = Green Roof Maintenance
| website = Columbia-green.com
| access-date =23 June 2017 
}}</ref> The maintenance energy use for green roofs has many variables, including: climate, intensity of rainfall, type of building, type of vegetation, and external coatings.<ref name="Saadatian et al 2013">{{cite journal |last1=Saadatian |first1=Omidreza |last2=Sopian |first2=K. |last3=Salleh |first3=E. |last4=Lim |first4=C.H. |last5=Riffat |first5=Safa |last6=Saadatian |first6=Elham |last7=Toudeshki |first7=Arash |last8=Sulaiman |first8=M.Y. |title=A review of energy aspects of green roofs |journal=Renewable and Sustainable Energy Reviews |date=July 2013 |volume=23 |pages=155–168 |doi=10.1016/j.rser.2013.02.022 |bibcode=2013RSERv..23..155S }}</ref> The most significant effect comes from scarce rainfall which will increase the maintenance energy due to the watering required. During a 10-year roof maintenance cycle a house with a green roof requires more retrofit embodied energy than a house with a white roof. The individual components of a green roof have {{CO2}} implications during the manufacturing process that are additional implications compared to a conventional roof.<ref>{{cite journal |last1=Bozorg Chenani |first1=Sanaz |last2=Lehvävirta |first2=Susanna |last3=Häkkinen |first3=Tarja |title=Life cycle assessment of layers of green roofs |journal=Journal of Cleaner Production |date=March 2015 |volume=90 |pages=153–162 |doi=10.1016/j.jclepro.2014.11.070 |bibcode=2015JCPro..90..153B }}</ref> The embodied energy for green roof components are {{convert|23.6|kg/m2|psf|0|abbr=in}} {{CO2}} of green roof. This value is equivalent to 6448 g C m<sup>−2</sup> which is significantly greater than 378 g C m<sup>−2.</sup><ref name="Saadatian et al 2013"/> Criteria for waste management practices when green roofs reach their end-of-life remain uncodified.<ref>{{Cite journal |last1=Rizzo |first1=Gianfranco |last2=Cirrincione |first2=Laura |last3=La Gennusa |first3=Maria |last4=Peri |first4=Giorgia |last5=Scaccianoce |first5=Gianluca |date=2023-01-04 |title=Green Roofs' End of Life: A Literature Review |journal=Energies |language=en |volume=16 |issue=2 |page=596 |doi=10.3390/en16020596 |doi-access=free |issn=1996-1073|hdl=10447/586396 |hdl-access=free }}</ref>

Both sod roofs and LWA-based (Lightweight Aggregates) roofs have been found to have a negative impact on the quality of their resulting runoff.<ref>{{cite journal |last1=Teemusk |first1=Alar |last2=Mander |first2=Ülo |title=The Influence of Green Roofs on Runoff Water Quality: A Case Study from Estonia |journal=Water Resources Management |date=November 2011 |volume=25 |issue=14 |pages=3699–3713 |doi=10.1007/s11269-011-9877-z |bibcode=2011WatRM..25.3699T |s2cid=154130342 }}</ref>

==Types==
[[File:Intensive extensive green roofs.png|thumb|right|An intensive and an extensive green roof]]
[[File:Torvtak 2.png|thumb|Section of a [[Gudbrandsdal]] type [[sod roof]] with elaborate "turf log"]]
Green roofs can be categorized as intensive, semi-intensive, or extensive, depending on the depth of the planting medium and the amount of maintenance they need. Extensive green roofs traditionally support {{convert|10|-|25|psf|kg/m2|-1|order=flip|abbr=in}} of vegetation<ref>[http://www.eot.state.ma.us/smartgrowth/07toolkit/LID/regional_planning/LID/green_roofs.html] {{webarchive|url=https://web.archive.org/web/20100703122305/http://www.eot.state.ma.us/smartgrowth/07toolkit/LID/regional_planning/LID/green_roofs.html|date=3 July 2010}}</ref> while intensive roofs support {{convert|80|-|150|psf|kg/m2|-1|order=flip|abbr=in}} of vegetation.<ref>{{cite web |url=http://www.raingardennetwork.com/greenroofs.htm |title=Green Roof |publisher=Raingardennetwork.com |access-date=15 August 2012 |archive-date=14 October 2012 |archive-url=https://web.archive.org/web/20121014210301/http://www.raingardennetwork.com/greenroofs.htm }}</ref> Traditional [[roof garden]]s, which require a reasonable depth of soil to grow large plants or conventional lawns, are considered intensive because they are labour-intensive, requiring irrigation, feeding, and other maintenance.  Intensive roofs are more park-like with easy access and may include anything from kitchen herbs to shrubs and small trees.<ref name="Seattle, 2007">{{cite web
 |title       = City Green Building – Green Roofs
 |website     = Seattle Department of Planning and Development
 |date        = 3 November 2008
 |url         = http://www.seattle.gov/dpd/greenbuilding/ourprogram/resources/technicalbriefs/dpds_009485.asp#whatis
 |archive-url  = https://web.archive.org/web/20080907154958/http://seattle.gov/dpd/GreenBuilding/OurProgram/Resources/TechnicalBriefs/DPDS_009485.asp#whatis
 |archive-date = 7 September 2008
}}</ref>

Extensive green roofs, by contrast, are designed to be virtually self-sustaining and should require only a minimum of maintenance, perhaps a once-yearly weeding or an application of slow-release fertilizer to boost growth.  Extensive roofs are usually only accessed for maintenance.<ref name="Seattle, 2007" /> They can be established on a very thin layer of soil (most use specially formulated composts): even a thin layer of [[Mineral wool|rockwool]] laid directly onto a watertight roof can support a planting of ''[[Sedum]]'' species and [[moss]]es.  Some green roof designs incorporate both intensive and extensive elements. To protect the roof, a waterproofing membrane is often used, which is manufactured to remain watertight in extreme conditions including constant dampness, ponding water, high and low alkaline conditions and exposure to plant roots, fungi and bacterial organisms.<ref name="Green (Planted) Roofs">{{cite web |title=Green (Planted) roofs |publisher=The Vinyl Roofing Division of the Chemical Fabrics & Film Association |date=22 June 2012 |url=http://vinylroofs.org/resources/green-planted-roofs/index.html}}</ref>

Advances in green roof technology have led to the development of new systems that do not fit into the traditional classification of green roof types. Comprehensive green roofs bring the most advantageous qualities of extensive and intensive green roofs together. Comprehensive green roofs support plant varieties typically seen in intensive green roofs at the depth and weight of an extensive green roof system.<ref>{{cite web |title=Comprehensive Green Roofs |author=Omni Ecosystems |date=9 March 2013 |url=http://www.omni-ecosystems.com/green-roof |archive-url=https://web.archive.org/web/20131209012756/http://www.omni-ecosystems.com/green-roof/ |archive-date=9 December 2013  }}</ref>

Another important distinction is between pitched green roofs and flat green roofs.  Pitched [[sod roof]]s, 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.

==History==
[[File:Authentic Viking recreation.jpg|thumb|left|Re-creation of [[Viking]] houses in [[Newfoundland and Labrador|Newfoundland]]]]
[[File:Heidal.jpg|thumb|left|Sod roofs on 18th-century farm buildings in [[Heidal]], Norway.]]In ancient times green roofs consisted of cave-like structures or [[sod roofs]] covered with earth and plants commonly used for agriculture, dwelling, and ceremonial purposes. These early shelters provided protection from the elements, good insulation during the winter months, and a cool location in the summer. Unfortunately for modern conveniences, these were neither waterproof nor was there any system to keep out unwanted burrowing wildlife.<ref name=":1">{{cite web | url=http://www.greenrooftechnology.com/history-of-green-roofs | title=History of Green Roof Technology, Green Walls, Living Walls|website=Green Roof Technology|first= Jörg |last=Breuning}}</ref>{{disputed inline|for=trad birchbark underlayer|date=October 2018}}

[[File:MEC's green roof among others.jpg|thumb|left|On the green roof of the [[Mountain Equipment Co-op]] store in [[Toronto|Toronto, Ontario]], Canada.]]
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.  However, green roofs or sod roofs in northern [[Scandinavia]] have been around for centuries.  The modern trend started when green roofs were developed in Germany in the 1960s, and has since spread to many countries.  Today, it is estimated that about 10% of all German roofs have been "greened".<ref name="hortweb1">{{cite web
 |url         = http://hortweb.cas.psu.edu/research/greenroofcenter/history.html
 |title       = Penn State Green Roof Research: About Green Roofs
 |website     = Hortweb.cas.psu.edu
 |access-date  = 10 June 2008
 |archive-url  = https://archive.today/20020824142025/http://hortweb.cas.psu.edu/research/greenroofcenter/history.html
 |archive-date = 24 August 2002
 }}</ref>

A number of European Countries have very active associations promoting green roofs, including Germany, Switzerland, the Netherlands, Norway, Italy, Austria, Hungary, Sweden, the UK, and Greece.<ref>{{cite web|url=http://www.efb-greenroof.eu |title=European Federation of Green Roof Associations – EFB |publisher=Efb-greenroof.eu |access-date=25 April 2012}}</ref> Germany was the first country to start developing green roof systems and market them on a large scale.<ref name=":1" /> The City of Linz in Austria has been paying developers to install green roofs since 1983, and in Switzerland, it{{Clarify|date=June 2024}} has been a federal law since the late 1990s.{{Citation needed|date=June 2024}}  In the UK, their uptake has been slow, but a number of cities have developed policies to encourage their use, notably London and Sheffield.

Green roofs are also becoming increasingly popular in North America, although they are not as common as in some parts of Europe. Numerous North American cities offer tax incentives to developers who integrate green roofs in their buildings. Toronto and San Francisco legally mandate new buildings to include green roofs.<ref>{{cite web |url=https://www1.toronto.ca/wps/portal/contentonly?vgnextoid=83520621f3161410VgnVCM10000071d60f89RCRD&vgnextchannel=3a7a036318061410VgnVCM10000071d60f89RCRD |title=City of Toronto Green Roof Bylaw |publisher=City of Toronto |access-date=17 December 2017 |archive-date=26 January 2018 |archive-url=https://web.archive.org/web/20180126040826/https://www1.toronto.ca/wps/portal/contentonly?vgnextoid=83520621f3161410VgnVCM10000071d60f89RCRD&vgnextchannel=3a7a036318061410VgnVCM10000071d60f89RCRD }}</ref><ref>{{cite web|url=http://sf-planning.org/san-francisco-better-roofs |title=San Francisco Better Roofs |publisher=City of San Francisco Planning Department |access-date=17 December 2017}}</ref>

Rooftop [[greywater treatment|water purification]] is also being implemented in green roofs.  These forms of green roofs are actually [[Waste stabilization pond|treatment ponds]] built into the rooftops.  They are built either from a simple substrate (as being done in [[Dongtan, Shanghai|Dongtan]]<ref>{{cite web |url=http://www.eukn.org/eukn/themes/Urban_Policy/Urban_environment/Environmental_sustainability/dongtan-eco-city_1348.html |title=EUKN |access-date=14 March 2008 |archive-url=https://web.archive.org/web/20071016104747/http://www.eukn.org/eukn/themes/Urban_Policy/Urban_environment/Environmental_sustainability/dongtan-eco-city_1348.html |archive-date=16 October 2007  }}</ref>) or with plant-based ponds. Plants used include [[calamus (palm)|calamus]], ''[[Menyanthes trifoliata]]'', ''[[Mentha aquatica]]'', etc.<ref>{{cite web|url=http://www.toontoelen.be/index.php?option=com_content&task=view&id=684&Itemid=58 |title=Dakvijvers |website=Toontoelen.be |access-date=23 June 2017}}</ref>)

Several studies have been carried out in Germany since the 1970s.{{Clarify|date=January 2025}} Berlin is one of the most important centers of green roof research in Germany. Particularly in the last 10 years, much more research has begun. About ten green roof research centers exist in the US and activities exist in about 40 countries. In a recent study on the impacts of [[green infrastructure]], in particular green roofs in the Greater Manchester area, researchers found that adding green roofs can help keep temperatures down, particularly in urban areas: "adding green roofs to all buildings can have a dramatic effect on maximum surface temperatures, keeping temperatures below the 1961–1990 current form case for all time periods and emissions scenarios. Roof greening makes the biggest difference…where the building proportion is high and the evaporative fraction is low.  Thus, the largest difference was made in the town centers".<ref>{{cite journal |last1=Gill |first1=S.E |last2=Handley |first2=J.F |last3=Ennos |first3=A.R |last4=Pauleit |first4=S |title=Adapting Cities for Climate Change: The Role of the Green Infrastructure |journal=Built Environment |date=13 March 2007 |volume=33 |issue=1 |pages=115–133 |doi=10.2148/benv.33.1.115 }}</ref>

==Brown roofs==
[[File:ESF-Gateway-Green-Roof-2014.jpg|thumb|upright|Roof planted with [[sand dune ecology|dune plants]] from the shores of Lake Ontario, [[State University of New York College of Environmental Science and Forestry|SUNY-ESF]], Syracuse, NY]]
Industrial [[brownfield]] 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", also known as "biodiverse roofs",<ref>{{cite web |url=http://www.brownroofs.co.uk/brown-roof-biodiversity.php |title=Brown Roofs and Biodiversity (Biodiverse Green Roofs) |access-date=10 September 2009 |archive-url=https://web.archive.org/web/20111017120946/http://www.brownroofs.co.uk/brown-roof-biodiversity.php |archive-date=17 October 2011  }}</ref> can partly mitigate this loss of habitat by covering the flat roofs of new developments with a layer of locally sourced material.  Construction techniques for brown roofs are typically similar to those used to create flat green roofs, the main difference being the choice of growing medium (usually locally sourced rubble, gravel, soil, etc...) to meet a specific biodiversity objective.<ref>{{cite web |url=http://greenroofs.org/grtok/materials_browse.php?id=59&what=view |title=Green Roofs Tree of Knowledge &#124; Browse Materials and Plants Research |access-date=25 May 2012 |archive-url=https://web.archive.org/web/20120319200626/http://www.greenroofs.org/grtok/materials_browse.php?id=59&what=view |archive-date=19 March 2012  }}</ref> In Switzerland, it is common to use alluvial gravels from the foundations; in London, a mix of brick rubble and some concrete has been used.

The original idea was to allow the roofs to self-colonise with plants, but they are sometimes seeded to increase their biodiversity potential in the short term. Such practices are derided by purists.<ref>{{cite web |url=http://www.brownroofs.co.uk/brown-roof-habitats.php |title=Creating Brown Roof Habitats |access-date=13 January 2012 |archive-url=https://web.archive.org/web/20120102070717/http://www.brownroofs.co.uk/brown-roof-habitats.php |archive-date=2 January 2012  }}</ref> The roofs are colonised by spiders and insects (many of which are becoming extremely rare in the UK as such sites are developed) and provide a feeding site for insectivorous birds.  [[Laban Dance Centre|Laban]], a centre for contemporary dance in London, has a brown roof specifically designed to encourage the nationally rare [[black redstart]].<ref>{{cite web |url=http://www.livingroofs.org/livingpages/caselaban.html |title=Frontpage |access-date=17 July 2008 |archive-url=https://web.archive.org/web/20080705085128/http://www.livingroofs.org/livingpages/caselaban.html |archive-date=5 July 2008  }}</ref> A green roof, {{cvt|160|m|ft}} above ground level, and claimed to be the highest in the UK and Europe "and probably in the world" to act as nature reserve, is on the [[One Churchill Place|Barclays Bank HQ]] in [[Canary Wharf]].<ref>{{cite news | url = https://www.theguardian.com/environment/2005/aug/12/conservationandendangeredspecies.uknews | title = Wildlife flourishes 32 floors above the Thames | newspaper = The Guardian}}</ref> Designed combining the principles of green and brown roofs, it is already home to a range of rare invertebrates.

== ASLA Award Green Roof Projects ==
[[File: CaliforniaAcademyofSciences.jpg|thumb|upright=1.25|The new [[California Academy of Sciences]] building in San Francisco's [[Golden Gate Park]] has a green roof that provides {{convert|2.5|acre|m2}} of native vegetation designed as a habitat for indigenous species, including the threatened [[Bay checkerspot butterfly]]. According to the Academy's fact sheet on the building, the building consumes 30–35% less energy than required by code.<ref>{{cite web|url= http://www.calacademy.org/geninfo/newsroom/releases/2005/Green_building_facts.html|title= California Academy of Sciences – Newsroom|access-date=10 June 2008|archive-url= https://web.archive.org/web/20080403122805/http://www.calacademy.org/geninfo/newsroom/releases/2005/Green_building_facts.html|archive-date=3 April 2008}}</ref>]]
* 2017 Award: Seeding Green Roofs for Greater Biodiversity and Lower Costs, Lincoln, NE, USA. ''Richard Sutton''
* 2013 Award: [[Green Roof Innovation Testing Laboratory]], Toronto, Ontario, Canada. ''John H. Daniels'', Brooklyn Botanic Garden Visitors Center, Brooklyn. ''HMWhite'', and NYC Parks Green Roof: A Living Laboratory for Innovative Green Roof Design, New York, NY. ''NYC Parks''
* 2012 Award: Lafayette Greens: Urban Agriculture, Urban Fabric, Urban Sustainability, Detroit. ''Kenneth Weikal Landscape Architecture'' 200 Fifth Avenue, NYC. ''Landworks Studio, Inc.''
* 2011 Award: Manassas Park Elementary School Landscape, Manassas Park, VA. Siteworks]
* 2009 Award: [[California Academy of Sciences]], San Francisco, CA. ''SWA Group'', Changi Airport Terminal 3 Interior Landscape, Singapore. ''Tierra Design (S) Pte Ltd'', Corporate Headquarters, San Francisco, CA. ''OLIN'', Macallen Building, South Boston, MA. ''Landworks Studio, Inc.'', and Museo del Acero Horno3, Monterrey, Mexico. ''Surfacedesign Inc.+ Harari arquitectos''
* 2008 Award: Gannett/USA Today Headquarters, McLean, Virginia. Michael Vergason Landscape Architects, Ltd.
* 2007 Award: Washington Mutual Center Roof Garden, Seattle, Washington. Phillips Farevaag Smallenberg
* 2002 Award: [[Chicago City Hall]] Green Roof, Chicago, Illinois. David Yocca

==Examples by country==
===Australia===
Green roofs have been increasing in popularity in Australia over the past 10 years.  Some of the early examples include the Freshwater Place residential tower in Melbourne (2002) with its Level 10 rooftop Half Acre Garden, CH2 building housing the Melbourne City Council (2006) – Australia's first 6-star Green Star Design commercial office building as certified by the [[Green Building Council of Australia]], and Condor Tower (2005) with a {{convert|75|m2|sqft|adj=on|abbr=off}} lawn on the 4th floor.

Since 2008, city councils and influential business groups in Australia have become active promoting the benefits of green roofs. "The Blueprint to Green Roof Melbourne" is one program being run{{when|date=January 2024}} by the [[Committee for Melbourne]].<ref>{{cite web|url=http://www.growingup.org.au/|title=Best Remodeling Ideas To Increase Your Home's Value -|website=Best Remodeling Ideas To Increase Your Home's Value|access-date=2 November 2010|archive-date=14 November 2010|archive-url=https://web.archive.org/web/20101114082219/http://www.growingup.org.au/}}</ref> In 2010, the largest Australian green roof project was announced.  The Victorian Desalination Project<ref>{{cite web|url=http://www.aquasure.com.au|title=Home|website=www.aquasure.com.au}}</ref> will have a "living tapestry" of 98,000 Australian indigenous plants over a roof area spanning more than {{convert|26000|m2|sqft|abbr=in}}. The roof will form part of the desalination plant's sophisticated roof system, designed to blend the building into the landscape, and provide acoustic protection, corrosion resistance, thermal control, and reduced maintenance.

[[File:Tillandsia Plant screen.jpg|thumb|Movable Tillandsia plant screen]]
In June 2014 ecological artist [[Lloyd Godman]], with structural engineer Stuart Jones and environmental scientist Grant Harris collaborated to install an experiment using [[Tillandsia]] plants in extreme outdoor conditions at levels 92, 91, 65 and 56 on [[Eureka Tower]] in Melbourne, Australia. The selected air plants are extremely light, and are able to grow with no soil or watering system, and the plants have been checked at regular intervals since their installation and are still growing and flowering. One species; [[Tillandsia bergeri]], has grown from a single shoot to several thriving colonies.

The project is now titled Tillandsia SWARM and has been expanded to include many other buildings across Australia, including Federation Square, National Gallery of Victoria and Essendon Airport.<ref>{{cite news|url=http://www.theage.com.au/victoria/extreme-gardening-on-the-92nd-floor-of-the-eureka-tower-20150323-1m45sm.html|title=Extreme gardening on the 92nd floor of the Eureka Tower|first=Aisha|last=Dow|date=23 March 2015|newspaper=The Age}}</ref> Godman has also experimented with Tillandsia plant screens that can be moved across skylights to create shade in summer and to allow in sun during winter. Temperature readings taken on a 40&nbsp;°C day in summer revealed that the surface temperature on the roof had reached 84&nbsp;°C, while the shadows cast by the plants had reduced the surface temperature on the roof to 51&nbsp;°C.

===Canada===
[[File:Wheatfield in Ottawa.jpg|right|thumb|The green roof on top of the [[Canadian War Museum]] in [[Ottawa]] looks like a wheatfield, with the towers of [[Parliament Hill|Canada's Parliament]] visible in the distance]]
The city of [[Toronto]] approved a by-law in May 2009<ref>{{Cite web|url=https://www.treehugger.com/corporate-responsibility/toronto-makes-green-roofs-the-law-approves-controversial-bike-lanes.html|title=Toronto Makes Green Roofs the Law, Approves Controversial Bike Lanes|website=TreeHugger}}</ref> mandating green roofs on residential and industrial buildings.  There is criticism from [[Steven W. Peck|Green Roofs for Healthy Cities]] that the new laws are not stringent enough, since they will only apply to residential building that are a minimum of six stories high. By 31 January 2011, industrial buildings were required to render 10% or {{cvt|2000|m2|sqft|abbr=in}} of their roofs green.<ref>{{cite news
  |url=https://www.theglobeandmail.com/news/national/council-approves-stringent-green-roof-rules/article1154619/
  |title=Council approves stringent green-roof rules
  |work=Globe and Mail |location=Toronto
  |date=23 August 2012
}}</ref> [[Toronto City Hall]]'s Podium roof was renovated to include a {{convert|32000|sqft|m2|abbr=in|order=flip}} rooftop garden, the largest publicly accessible roof in the city.  The green roof was opened to the public in June 2010.<ref>{{cite web
|url=http://www.toronto.ca/nps/revitalization/greenpodiumroof/
|title=Toronto City Hall's Podium Green Roof
|location=Toronto, Ontario, Canada
|work=City of Toronto
|date=27 June 2013
}}</ref> Many green roofs in Canada also use sustainable [[Rainwater harvesting in Canada|rainwater harvesting]] practices.

In 2008, the [[Vancouver Convention Centre]] installed a {{convert|6|acre|ha|adj=on|abbr=off|order=flip}} living roof of indigenous plants and grasses on its West building, making it the largest green roof in Canada.<ref>{{cite web|url=http://www.greenroofs.com/projects/pview.php?id=545 |title=Projects – Vancouver Convention Centre Expansion Project |website=Greenroofs.com |access-date=23 June 2017}}</ref>
The new [[Canadian War Museum]] in [[Ottawa]], opened in 2005, also features a grass-covered roof.

During the renovation of the [[Hamilton City Hall]] in [[Hamilton, Ontario]] that spanned from 2007 to 2010, many efforts were taken to enhance the environmentally friendly nature of the structure, which included the addition of a grass-covered roof.<ref>{{cite web|author=Ryan McGreal |url=http://raisethehammer.org/article/1092/city_hall_reno_photo_tour:_part_2 |title=City Hall Reno Photo Tour: Part 2 |publisher=Raise the Hammer |access-date=23 June 2017}}</ref>

[[Simon Fraser University]]'s [[Burnaby]] campus contains a substantial number of green roofs.<ref>{{cite web | url=https://www.burnaby.ca/City-Services/Planning/Environmental-Planning/Green-Development.html?PageMode=Print | title=Green Development | access-date=7 August 2017 | archive-date=7 August 2017 | archive-url=https://web.archive.org/web/20170807194606/https://www.burnaby.ca/City-Services/Planning/Environmental-Planning/Green-Development.html?PageMode=Print }}</ref>

Canada's first LEED Platinum V4 Home in Wakefield QC, EcoHome's Edelweiss House,<ref>{{Cite web|url=https://www.ecohome.net/guides/1204/canadas-first-leed-v4-platinum-house/ |title=Canada's first LEED V4 Platinum house|website=www.ecohome.net}}</ref> has a living Green Roof which is sloped at 12 degrees.

===Costa Rica===
Living green roofs have been built and grown at Saint Michael's Sustainable Community since 2012. Native plants, mostly flowers chosen for the environment, maximum shade and mass provide a colorful and functional living roof. The community has the largest number of green roofs in the country.

===Egypt===
In [[Egypt]], soil-less agriculture is used to grow plants on the roofs of buildings.  No soil is placed directly on the roof itself, thus eliminating the need for an insulating layer; instead, plants are grown on wooden tables.  Vegetables and fruit are the most popular candidates, providing a fresh, healthy source of food that is free from pesticides.<ref>{{cite web |url=http://weekly.ahram.org.eg/2005/745/en2.htm |title=Al-Ahram Weekly &#124; Environment &#124; May your roof be green |publisher=Weekly.ahram.org.eg |date=8 June 2005 |access-date=25 April 2012 |archive-url=https://web.archive.org/web/20120703190639/http://weekly.ahram.org.eg/2005/745/en2.htm |archive-date=3 July 2012  }}</ref>

A more advanced method, ([[aquaponics]]), being used experimentally in Egypt, is farming fish next to plants in a closed cycle.  This allows the plants to benefit from the ammonia excreted by the fish, helping the plants to grow better and at the same time eliminating the need for changing the water for the fish, because the plants help to keep it clean by absorbing the ammonia.  The fish also get some nutrients from the roots of the plants.

===Finland===
In Finland, green roofs are still scarce. Some experimental green roofs have been built in big cities. However, the capital city of Helsinki has published guidelines for enhancing the building of green roofs in the city. There is on-going research on the topic as the conditions in the southern Europe are very different from those in the north and knowledge acquired there can't be directly applied to colder climates. The fifth dimension – [https://www.researchgate.net/project/Fifth-Dimension-Green-Roofs-and-Walls-in-Urban-Areas-research-program Green roofs and walls in urban areas -research program] aims to produce high-level scientific and broadly applicable knowledge on optimal green roof and -wall solutions in Finland.

===France===
[[File:Green Roof at Vendée Historial, les Lucs.jpg|thumb|Green roof planted with native species at L'Historial de la Vendée, a new museum in western France]]
In France, an {{convert|8000|m2|sqft|abbr=in}} extensive, cable-supported green roof has been created on the International School in Lyon.<ref>{{cite web |url=http://www.greenroofs.com/chic_sustainability.htm |title=Chic Sustainability |publisher=Greenroofs.com |date=14 March 2006 |access-date=25 April 2012 |archive-url=https://web.archive.org/web/20120503071548/http://www.greenroofs.com/chic_sustainability.htm |archive-date=3 May 2012  }}</ref> Another huge green roof of roughly {{convert|8000|m2|sqft|abbr=in}} has been incorporated into the new museum [[L'Historial de la Vendée]] which opened in June 2006 at [[Les Lucs-sur-Boulogne]].

===Germany===
Long-held green roof traditions started in the early industrialization period more than 100 years ago exist in Germany.  In the 1970s, green roof technology was elevated to the next level. Serious storm-water issues made cities think about innovative solutions, preferably with living plants. Modern green roof technology with high performance, lightweight materials were used to grow hardy vegetation even on roofs that can hardly support any additional load. In the 1980s modern green roof technology was common knowledge in Germany while it was practically unknown in any other country in the world. In Stuttgart, with one of the most innovative Department of Parks and Recreation and with the world's oldest horticultural Universities, modern green roof technology was perfected and implemented on a large scale. By the early 2000s, Germany had laws mandating that many metropolitan areas have green roofs.<ref>{{Cite journal |last1=Oberndorfer |first1=Erica |last2=Lundholm |first2=Jeremy |last3=Bass |first3=Brad |last4=Coffman |first4=Reid R. |last5=Doshi |first5=Hitesh |last6=Dunnett |first6=Nigel |last7=Gaffin |first7=Stuart |last8=Köhler |first8=Manfred |last9=Liu |first9=Karen K. Y. |last10=Rowe |first10=Bradley |date=2007-11-01 |title=Green Roofs as Urban Ecosystems: Ecological Structures, Functions, and Services |journal=BioScience |volume=57 |issue=10 |pages=823–833 |doi=10.1641/b571005 |issn=1525-3244}}</ref>

With the first green roof industry boom in Germany there were quality issues recorded. The FLL formed a committee that is focused on modern green roof technology. FLL stands for Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V. (German Landscape Research, Development and Construction Society). The FLL is an independent non-profit organization. It was founded in 1975 by eight professional organizations for "the improvement of environmental conditions through the advancement and dissemination of plant research and its planned applications". The FLL green roof working group is only one of 40 committees which have published a long list of guidelines and labor instructions. Some of these guidelines also available in English including the German FLL-Guideline for the Planning, Execution and Upkeep of Green-Roof Sites. The results of the research and synthesis done by FLL members are constantly updated and promulgated utilizing the same principles which govern the compilation of DIN standards and are published as either guiding principles or labor instructions.

The current Green Roof Guideline was published in 2011.<ref>{{cite web |url=http://www.greenrooftechnology.com/_literature_98993/Introduction_to_the_German_FLL_-_Guideline_for_Green_Roofs_2011 |title=Archived copy |access-date=1 March 2015 |archive-url=https://web.archive.org/web/20160304041742/http://www.greenrooftechnology.com/_literature_98993/Introduction_to_the_German_FLL_-_Guideline_for_Green_Roofs_2011 |archive-date=4 March 2016  }}</ref>
Today most elements of the German FLL are part of standards and guidelines around the world (FM Global, ASTM, NRCA, SPRI etc.).

Fachvereinigung Bauwerksbegrünung (FBB) was founded in 1990 as the second green roof association after DDV (Deutscher Dachgaertner Verband) in 1985. FBB was founded as an open forum for manufacturers and planners, merchants and operators in 1990. The organization was born from the then-visionary idea of understanding the relationship between nature and constructions not as oppositional, but as an opportunity. Both the green roofing and conventional roofing industries are equally represented.
The FBB has developed to become an innovative lobbying group with a strong market presence, internationally known through its cooperation with other European associations. Today, approximately 100 member companies use the multifaceted services offered by FBB, which offers a greater degree of market expertise and competitiveness. "Kompetenz im Markt".

Today, about {{convert|10000000|m2|sqft|abbr=in}} of new green roofs are being constructed each year. According latest studies about {{frac|3|4}} of these are extensive; the last {{frac|1|4}} are roof gardens. The cities with the most green roofs in Germany are Berlin and [[Stuttgart]].  Surveys about the status of regulation are done by the FBB.  Nearly one third of all German cities have regulations to support green-roof and rain-water technology.  Green-roof research institutions are located in several cities as including [[Hannover]], Berlin, [[Geisenheim]] and [[Neubrandenburg]].

Germany is the country with the most green roofs in the world as well as the country with the most advanced knowledge in modern green roof technology.<ref>{{Cite journal|date=2014-06-01|title=A comprehensive study of green roof performance from environmental perspective|journal=International Journal of Sustainable Built Environment|language=en|volume=3|issue=1|pages=127–134|doi=10.1016/j.ijsbe.2014.05.001|issn=2212-6090|last1=Li|first1=W.C.|last2=Yeung|first2=K.K.A.|doi-access=free}}</ref> Green roofs in Germany are part of the 2 –3 years apprentice educations system of landscaping professionals.

===Greece===
[[File:The Treasury - Syntagma.jpg|thumb|The ''oikostegi'', a green roof on the Treasury building in Athens]]
The Greek Ministry of Finance has now installed a green roof on the Treasury in Constitution Square in Athens.<ref>{{cite web |url=http://www.mnec.gr/el/press_office/DeltiaTypou/articles/article0933.html |title=Διαδικτυακή Πύλη Υπουργείου Οικονομικών – Κεντρική Σελίδα |publisher=Mnec.gr |date=20 April 2012 |access-date=25 April 2012 |archive-url=https://web.archive.org/web/20090418212542/http://www.mnec.gr/el/press_office/DeltiaTypou/articles/article0933.html |archive-date=18 April 2009  }}</ref> The so-called "oikostegi" (Greek – ''oiko'', {{IPA|el|ˈiko|pron}}, meaning building-ecological, and ''stegi'', pronounced ''staygee'', meaning roof-abode-shelter) was inaugurated in September 2008.  Studies of the thermodynamics of the roof in September 2008 concluded that the thermal performance of the building was significantly affected by the installation.<ref>{{cite web |url=http://www.mech.ntua.gr/gr/staff/DEP/rogdakis_gr |title=Σχολή Μηχανολόγων Μηχανικών Ε.Μ.Π. – Μέλος ΔΕΠ |publisher=Mech.ntua.gr |access-date=25 April 2012 |archive-url=https://web.archive.org/web/20120502231758/http://www.mech.ntua.gr/gr/staff/DEP/rogdakis_gr |archive-date=2 May 2012  }}</ref> In further studies, in August 2009, energy savings of 50% were observed for air conditioning in the floor directly below the installation.  The ten-floor building has a total floor space of {{convert|1.4|ha|acre|abbr=off}}.  The oikostegi covers {{convert|650|sqft|abbr=in}}, equalling 52% of the roof space and 8% of the total floor space.  Despite this, energy savings totalling €5,630 per annum were recorded, which translates to a 9% saving in air conditioning and a 4% saving in heating bills for the whole building.<ref>{{cite web|url=http://oikosteges.gr/index.php/greenroofs/research |title=Μελέτες |publisher=Oikosteges.gr |date=24 September 2009 |access-date=25 April 2012}}</ref> An additional observation and conclusion of the study was that the thermodynamic performance of the oikostegi had improved as biomass was added over the 12 months between the first and second study.  This suggests that further improvements will be observed as the biomass increases still further.  The study also stated that while measurements were being made by thermal cameras, a plethora of beneficial insects were observed on the roof, such as butterflies, honey bees and ladybirds. Obviously this was not the case before installation.  Finally, the study suggested that both the micro-climate and biodiversity of Constitution Square, in Athens, Greece had been improved by the oikostegi.

===Iceland===
[[File:Church at Hof.jpg|right|thumb|Sod roof Church at Hof, Iceland]]
[[Sod roof]]s are frequently found on traditional farmhouses and farm buildings in [[Iceland]].<ref>{{cite web |url=http://www.greenroofs.com/Greenroofs101/history.htm |title=Greenroofs101: History |publisher=Greenroofs.com |access-date=15 August 2012 |archive-url=https://web.archive.org/web/20120710073115/http://www.greenroofs.com/Greenroofs101/history.htm |archive-date=10 July 2012 }}</ref>

===India===
Green roofs called Burze Pash were traditionally used in [[Kashmir]]i houses to provide insulation during winters. The rooftops were made from locally sourced [[birch wood]], and covered with a fertile layer of soil, on which different flowers and even crops would be grown. The variety of flowers and crops frequently varied by region, creating diversity.<ref>{{cite news |last= |first= |date=17 August 2018|title=Burza Pash: The rooftops that exploded with colours|url=https://www.greaterkashmir.com/opinion/burza-pash-the-rooftops-that-exploded-with-colours/|newspaper=Greater Kashmir|access-date= 7 March 2025}}</ref>

=== Malaysia ===
Bus stops in [[Kuala Lumpur]] were fitted with green roofs in 2019.<ref name=":3">{{Cite web |last=Bailey |first=Stephanie |date=2019-06-03 |title=Green roofs are sprouting up on buses |url=https://www.cnn.com/2019/06/03/health/green-roofs-singapore-buses-intl/index.html |access-date=2023-04-24 |website=CNN |language=en}}</ref>

=== Poland ===
Several cities in Poland have implemented policies and incentives to encourage the installation of green roofs, including Warsaw, Krakow, and Wroclaw. These policies have helped to increase the adoption of green roofs in the country, particularly in urban areas, where they are seen as an important tool for mitigating the environmental impacts of urbanization and improving the quality of life for city residents. The [[University of Warsaw]] green roof is one of the most impressive and well-known examples of green roofs in Poland. It covers an area of approximately 10,000 square meters and includes over 30,000 plants from more than 70 different species.<ref>{{Cite web |title=Is the World's Greatest Green Roof in Warsaw, Poland? {{!}} Smart Cities Dive |url=https://www.smartcitiesdive.com/ex/sustainablecitiescollective/world-s-greatest-green-roof-warsaw-poland/24098/ |access-date=2023-03-30 |website=www.smartcitiesdive.com |language=en-US}}</ref>

=== Singapore ===
[[File:GreenRoof-SingaporeBotanicGardens.jpg|thumb|Green roof at [[Singapore Botanic Gardens]]]]
[[Singapore]] installed a green roof on a bus in 2019 as part of an experiment led by researchers at the [[National University of Singapore]].<ref name=":3" /> Green roofs on bus stops in Singapore were found to reduce ambient temperatures by up to 2C.<ref>{{Cite web |title=Grass roofs on 30 bus stops in S'pore, can lower ambient temperatures by around 2°C |url=https://mothership.sg/2022/09/grass-green-roof-bus-stops/ |access-date=2023-04-24 |website=mothership.sg |language=en}}</ref>

===Switzerland===
Switzerland has one of Europe's oldest green roofs, created in 1914 at the Moos lake water-treatment plant, [[Wollishofen]], [[Zürich]].  Its filter tanks have {{convert|30000|m2|sqft|abbr=in}} of flat concrete roofs.  To keep the interior cool and prevent bacterial growth in the filtration beds, a drainage layer of gravel and a {{convert|15|cm|in|adj=on|abbr=off}} layer of soil was spread over the roofs, which had been waterproofed with [[Bitumen|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]]).  More recent Swiss examples can be found at Klinikum 1 and Klinikum 2, the [[Cantons of Switzerland|Cantonal]] Hospitals of [[Basel]], and the [[Sihlpost]] platform at Zürich's main railway station.

===Sweden===
What is claimed<ref>{{cite web|url=http://www.greenroof.se/?pid=38&sub=20 |title=Green Roof – Augustenborg's Botanical Roof Garden – History |publisher=Greenroof.se |access-date=25 April 2012}}</ref> to be the world's first green roof [[botanical garden]] was set up in [[Augustenborg, Malmö|Augustenborg]], [[Malmö]] 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 SGRI botanical garden incorporates green roofs and extensive landscaping of streams, ponds, and soak-ways between the buildings to deal with storm water run-off. The Augustenborg's Botanical Roof Garden is no longer open to visitors and the Scandinavian green roof institute is since mid 2025 no longer operational. Some of the work for promoting green roofs in Sweden is now carried on by the Scandinavian green infrastructure association, a NGO linked to the former institute. 

The new [[Bo01]] urban residential development (in the [[Västra Hamnen]] (Western Harbour) close to the foot of the [[Turning Torso]] office and apartment block, designed by [[Santiago Calatrava]]) is built on the site of old shipyards and industrial areas, and incorporates many green roofs.

In 2012, the shopping mall [[Emporia (shopping mall)|Emporia]] with its {{convert|27000|m2|sqft|adj=on|abbr=off}} roof garden, was opened. The size of the roof garden is approximately equivalent to 4 soccer fields, which makes it one of the biggest green roof parks in Europe that is accessible to the public.

===United Kingdom===
[[File:Sky Garden Kanes Foods Green Roof.JPG|thumb|The Sky Garden Wildflower Roof topping the Kanes Salad Factory, Evesham]]
In 2003 English Nature concluded that 'in the UK policy makers have largely ignored green roofs'.<ref>Grant, G., Engleback, L., and Nicholson, B., ''Green Roofs: their existing status and potential for conserving biodiversity in urban areas [Report No. 498]'', Publisher: English Nature Reports (2003)</ref> However, British examples can be found with increasing frequency. The [[Kensington Roof Gardens]] are a notable early roof garden which was built above the former [[Derry & Toms]] department store in [[Kensington]], London in 1938.<ref>{{cite web |url=http://www.londongardensonline.org.uk/gardens-online-record.asp?ID=KAC055 |title=London Gardens Online |publisher=London Gardens Online |access-date=25 April 2012 |archive-date=18 March 2012 |archive-url=https://web.archive.org/web/20120318010119/http://www.londongardensonline.org.uk/gardens-online-record.asp?ID=KAC055 }}</ref> More recent examples can be found at the [[University of Nottingham]] [[Jubilee Campus]], and in London at [[Sainsbury's Millennium Store]] in Greenwich, the [[Horniman Museum]] and at [[Canary Wharf]].  The Ethelred Estate, close to the River [[Thames]] in central London, is the British capital's largest roof-greening project to date.  [[Toxteth]] in Liverpool is also a candidate for a major roof-greening project.

In the United Kingdom, intensive green roofs are sometimes used in built-up city areas where residents and workers often do not have access to gardens or local parks.  Extensive green roofs are sometimes used to blend buildings into rural surroundings, for example by [[Rolls-Royce Motor Cars]], who has one of the biggest green roofs in Europe (covering more than {{convert|32000|m2|sqft|abbr=in}} on their factory at Goodwood, West Sussex.<ref>[http://www.rolls-roycemotorcars.com/the-company/environmental/#LivingRoof] {{webarchive|url=https://web.archive.org/web/20140103075110/http://www.rolls-roycemotorcars.com/the-company/environmental/|date=3 January 2014}}</ref>

The University of Sheffield has created a Green Roof Centre of Excellence and conducted research, particularly in a UK context, into green roofs.<ref>{{cite web|title=Green Roof Research|url=https://sites.google.com/a/sheffield.ac.uk/grr/|access-date=12 April 2021|publisher=The Green Roof Centre}}</ref> [[Nigel Dunnett]] of Sheffield University published a UK-centric book about green roofing in 2004 (updated 2008).<ref>Dunnett, N., Kingsbury, N., ''Planting Green Roofs and Living Walls'', Publisher: Timber Press (2004)</ref>

[[Fort Dunlop]] has the largest green roof in the UK since its redevelopment between 2004 and 2006.

The UK also has one of the most innovative food preparation facilities in Europe, the Kanes salad factory in [[Evesham]].<ref>{{cite web|url=http://www.fstoppress.com/articles/wild-flower-roof/|title=F Stop Press – Specialists in News and PR in the Midlands|website=www.fstoppress.com|access-date=23 June 2017|archive-url=https://web.archive.org/web/20160304082902/http://www.fstoppress.com/articles/wild-flower-roof/|archive-date=4 March 2016}}</ref> It is topped with a wildflower roof featuring nearly 90 species of wildflower and natural grasses. The seed mix was prepared in consultation with leading ecologists to try to minimise the impact on the local environment.<ref>{{cite web|url=http://kanesfoods.co.uk/sustainability-home/eco-factory/|title=Eco Factory « Kanes Foods|website=kanesfoods.co.uk}}</ref> The pre-grown wildflower blanket sits on top of a standing seam roof and is combined with solar panels to create an eco-friendly finish to the entire factory.<ref>{{Cite news|url=https://www.bbc.co.uk/news/uk-england-hereford-worcester-18724335|title=Worcestershire garden roof salad factory opens|date=5 July 2012|publisher=Bbc.co.uk|newspaper=BBC News}}</ref> The development also won the 2013 National Federation of Roofing Contractors Sustainable Roof Award for Green Roofing.<ref>{{cite web|url=http://www.sky-garden.co.uk/gallery/kanes.php|title=Kanes Foods Wildflower Blanket Green Roof – Gallery – Sky Garden|website=www.sky-garden.co.uk}}</ref><ref>{{cite web|url=http://www.nfrc.co.uk/roofing-awards-2013|title=The National Federation of Roofing Contractors|website=The National Federation of Roofing Contractors}}</ref>

===United States===
[[File:Green City.jpg|thumb|An intensive roof garden in [[New York City]]]]
[[File:Roof garden 3 (4694438648).jpg|thumb|alt=Roof garden in New York|Roof garden in New York]]
[[File:20080708 Chicago City Hall Green Roof.JPG|thumb|Green roof of [[Chicago City Hall]]]]
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[[File:CalifAcadSciRoof 0820.JPG|thumb|upright|A modern green roof at [[California Academy of Sciences]]<ref>''California'' (magazine of the University of California Alumni Association), Sept/Oct 2008, cover and pp. 52–53</ref>]]
One of the largest expanses of extensive green roof is to be found in the US, at [[Ford Motor Company]]'s [[River Rouge Plant]], [[Dearborn, Michigan|Dearborn]], Michigan, where {{convert|42000|m2|sqft|order=flip}} of assembly plant roofs are covered with [[sedum]] and other plants, designed by [[William McDonough]]; the $18 million assembly avoids the need of what otherwise would be $50 million worth of mechanical treatment facilities on site. Built over Millennium Park Garage, Chicago's {{convert|24.5|acre|ha|adj=on}} [[Millennium Park]] is considered one of the largest intensive green roofs.<ref>{{cite web|last=Nelson |first=Bryn |url=http://www.nbcnews.com/id/24056306 |archive-url=https://web.archive.org/web/20131225060228/http://www.nbcnews.com/id/24056306/ |archive-date=25 December 2013 |title=Green roofs popping up in big cities – Business – Going Green |publisher=NBC News |date=15 April 2008 |access-date=25 April 2012}}</ref> Other well-known American examples include Chicago's City Hall and the former Gap headquarters, now the headquarters of YouTube, in San Bruno, CA. The U.S. military has two major green roofs in the [[Washington metropolitan area|Washington, D.C. area]]: the [[United States Coast Guard|U.S. Coast Guard]] headquarters ({{convert|550000|sqft|m2|disp=or}}) and [[the Pentagon]] ({{convert|180000|sqft|m2|disp=or}}).{{citationneeded|date=December 2024}}<!--Recently, the [[American Society of Landscape Architects]] retrofitted their existing headquarters building in Washington, D.C. with a green roof designed by landscape architect [[Michael Van Valkenburgh]].<ref>{{cite web|url=http://www.asla.org/greenroof|title=ASLA Green Roof Demonstration Project}}</ref>

Another example of a green roof in the United States is the Ballard Library in Seattle.  This green roof has over 18,000 plants to help with insulation and reduce runoff.  The plants used on the roof include ''[[Achillea tomentosa]]'' (woolly yarrow), ''[[Armeria maritima]]'' (sea pink, sea thrift), ''[[Carex inops]] pensylvanica'' (long-stoloned sedge), ''[[Eriophyllum lanatum]]'' (Oregon sunshine), ''[[Festuca rubra]]'' (red creeping fescue), ''[[Festuca idahoensis]]'' (Idaho fescue), ''[[Phlox subulata]]'' (creeping phlox), ''[[Saxifraga caespitosa]]'' (tufted saxifrage), ''[[Sedum oreganum]]'' (Oregon stonecrop), ''[[Sedum album]]'' (white stonecrop), ''[[Sedum spurium]]'' (two-row stonecrop), ''[[Sisyrinchium idahoense]]'' (blue-eyed grass), ''[[Thymus serpyllum]]'' (wild thyme), ''[[Triteleia hyacinthina]]'' (fool's onion).
-->

An early green-roofed building (completed in 1971) is the {{convert|358000|sqft|m2|adj=on}} Weyerhaeuser Corporate Headquarters building in Federal Way, Washington.  Its 5-story office roof system comprises a series of stepped terraces covered in greenery.  From the air, the building blends into the landscape.

The largest green roof in New York City was installed in midtown [[Manhattan]] atop the [[United States Postal Service]]'s Morgan Processing and Distribution Center.  Construction on the {{convert|109000|sqft|m2|adj=on}} project began in September 2008, and was finished and dedicated in July 2009.  Covered in native vegetation and having an expected lifetime of fifty years, this green roof will not only save the USPS approximately $30,000 a year in heating and cooling costs, but will also significantly reduce the amount of storm water contaminants entering the municipal water system.<ref>{{cite web |title = USPS News Release: U.S. Postal Service Opens First Green Roof |date = 22 July 2009 |url = http://www.usps.com/communications/newsroom/2009/pr09_063.htm |access-date = 11 February 2011 |archive-url = https://web.archive.org/web/20101231222639/http://www.usps.com/communications/newsroom/2009/pr09_063.htm |archive-date = 31 December 2010 }}</ref><ref>{{cite web | url = http://www.usps.com/communications/newsroom/greennews/pdf/greenkit_5.pdf | title=Green Roof: Morgan Processing and Distribution Center (P&DC) |access-date=3 March 2014 |archive-url= https://web.archive.org/web/20140801200244/http://www.capitolroofinginc.com/wp-content/uploads/2014/03/greenkit-5.pdf |archive-date= 1 August 2014}}</ref>
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Atop the [[Museum of Modern Art]] is a modern sculptural garden spanning over {{convert|16,750|sqft|m2}}. This rooftop is physically inaccessible to the public but has some of the most visible rooftop space in New York. [[Ken Smith (architect)|Ken Smith]] designed MoMA rooftop as a Landscape Architect by using 185 plastic rocks, 560 artificial boxwoods, {{convert|300|lb|kg}} of clear crushed glass, {{cvt|4|ST|t}} of recycled rubber mulch. His design was awarded the [[American Society of Landscape Architecture]] for design in 2009.
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In 2001, atop [[Chicago City Hall]], the {{convert|38800|sqft|adj=on}} roof gardens were completed, serving as a pilot project to assess the impact green roofs would have on the [[heat island]] effect in urban areas, rainwater runoff, and the effectiveness of differing types of green roofs and plant species for Chicago's climate. Although the rooftop is not normally accessible to the public, it is visually accessible from 33 taller buildings in the area. The garden consists of 20,000 plants of more than 150 species, including shrubs, vines and two trees. The green roof design team was headed by the Chicago area firm Conservation Design Forum in conjunction with noted "green" architect [[William McDonough]]. With an abundance of flowering plants on the rooftop, beekeepers harvest approximately {{convert|200|lb|kg|-1}} of honey each year from hives installed on the rooftop. Tours of the green roof are by special arrangement only. Chicago City Hall Green Roof won merit design award of the [[American Society of Landscape Architecture]] (ASLA) competition in 2002.

The {{convert|14000|sqft|m2}} of outdoor space on the seventh floor of [[Zeckendorf Towers]], formerly an undistinguished rooftop filled with potted plants, make up the largest residential green roof in New York.<ref name="zeckendorftowers" /><ref>[http://www.dnainfo.com/20101116/murray-hill-gramercy/union-squares-zeckendorf-towers-unveil-citys-largest-green-roof Zeckendorf Towers Unveils City's Largest Green Roof] {{webarchive|url=https://web.archive.org/web/20110120014828/http://www.dnainfo.com/20101116/murray-hill-gramercy/union-squares-zeckendorf-towers-unveil-citys-largest-green-roof |date=20 January 2011 }}, DNAinfo, 16 November 2010.</ref><ref>[https://www.nytimes.com/2010/12/26/realestate/26posting.html A New Roof That Works for a Living], ''[[The New York Times]]'', 23 December 2010.</ref> The roof was transformed in 2010 as part of Mayor [[Michael Bloomberg]]'s NYC Green Infrastructure campaign, and supposedly serves to capture some of the rain that falls on it rather than letting it run off and contribute to flooding in the adjacent [[14th Street – Union Square (New York City Subway)|Union Square subway station]].<ref name="zeckendorftowers">[http://zeckendorftowers.com/wp-content/uploads/2011/08/ZT-Rooftop.pdf One Union Square East Opens City's Largest Residential Green Roof], Zeckendorf Towers press release of 15 November 2010.</ref>

Some cost can also be attributed to maintenance.  Extensive green roofs have low maintenance requirements but they are generally not maintenance free.  German research has quantified the need to remove unwanted seedlings to approximately 6 seconds/m<sup>2</sup>/year.<ref>{{cite magazine|magazine=Deutscher Gartenbau|author=Kolb, W.|author2=Schwarz, T.|year=2002|title=Gepflegtes grün auf dem dach|language=de|issue=7|pages=32–34}}</ref> Maintenance of green roofs often includes fertilization to increase flowering and succulent plant cover.  If aesthetics are not an issue, fertilization and maintenance are generally not needed.  Extensive green roofs should only be fertilized with controlled-release fertilizers in order to avoid pollution of the storm water.  Conventional fertilizers should never be used on extensive vegetated roofs.<ref>{{cite journal |last1=Emilsson |first1=Tobias |last2=Czemiel Berndtsson |first2=Justyna |last3=Mattsson |first3=Jan Erik |last4=Rolf |first4=Kaj |title=Effect of using conventional and controlled release fertiliser on nutrient runoff from various vegetated roof systems |journal=Ecological Engineering |date=March 2007 |volume=29 |issue=3 |pages=260–271 |doi=10.1016/j.ecoleng.2006.01.001 |bibcode=2007EcEng..29..260E }}</ref><ref>{{cite journal |last1=Berndtsson |first1=J |last2=Emilsson |first2=T |last3=Bengtsson |first3=L |title=The influence of extensive vegetated roofs on runoff water quality |journal=Science of the Total Environment |date=15 February 2006 |volume=355 |issue=1–3 |pages=48–63 |doi=10.1016/j.scitotenv.2005.02.035 |pmid=16442432 |bibcode=2006ScTEn.355...48B }}</ref> German studies have approximated the nutrient requirement of vegetated roofs to 5&nbsp;gN/m<sup>2</sup>.  It is also important to use a substrate that does not contain too many available nutrients.  The FLL guidelines specify maximum-allowable nutrient content of substrates.<ref>{{cite web|url=http://www.fll.de |title=FLL: Startseite |website=Fll.de |access-date=23 June 2017}}</ref>

One of the oldest American green roofs in existence is atop the Rockefeller Center in Manhattan, built in 1936. This roof was primarily an aesthetic undertaking for the enjoyment of the center's workers, and remains to this day, having been refurbished in 1986.<ref>{{cite web|url=http://www.greenroofs.com/projects/pview.php?id=666 |title=Projects – Rockefeller Center Roof Gardens |website=Greenroofs.com |access-date=23 June 2017}}</ref>

With the passage of Denver's Green Roof Initiative<ref>{{cite web|title=Denver's Green Roof Initiative|url=https://www.denvergov.org/content/denvergov/en/denver-development-services/commercial-projects/green-roof-initiative.html|website=DenverGov}}</ref> in the November 2017 elections, effective January 2018, new buildings or existing buildings meeting the initiative's thresholds are required to have rooftop gardens, optionally combined with solar photovoltaic panels.<ref>{{cite web|last1=Murray|first1=Jon|title=Initiated Ordinance 300: Denver Green Roof Initiative|url=http://www.denverpost.com/2017/10/06/initiated-ordinance-300-denver/|website=The Denver Post|date=6 October 2017}}</ref><ref>{{cite web|last1=Chow|first1=Lorraine|title=Denver Becomes Latest City to Require Green Roofs|url=https://www.ecowatch.com/denver-green-roofs-2508372741.html|website=EcoWatch|access-date=17 November 2017|language=en|date=10 November 2017}}</ref>

[[Seattle]] is another city in which green roofs have been used on an increasing basis. This phenomenon is in large part due to efforts on behalf of the city to encourage green roofs through new and improved [[building code]]s. In 2006, the Seattle Green Factor program was approved.<ref name="stiffler">{{cite news |last1=Stiffler |first1=Lisa |title=City of Seattle wants more eco-friendly 'green roofs' |url=https://www.seattlepi.com/local/article/City-of-Seattle-wants-more-eco-friendly-green-900124.php |newspaper=Seattle Post-Intelligencer |date=23 September 2010 |access-date=16 November 2019}}</ref> The program rewards the incorporation of landscaping in new building developments in an attempt to reduce [[stormwater]] runoff and associated pollution, stabilize temperatures, and create habitats for birds and insects.<ref>{{cite web |title=Seattle Green Factor |url=http://www.seattle.gov/sdci/codes/codes-we-enforce-%28a-z%29/seattle-green-factor |website=Seattle.gov |access-date=17 November 2019}}</ref> These changes were expanded in 2009 to recognize the specific stormwater benefits of green roofs, and to reward developers who used them accordingly.<ref name="stiffler" /><ref name="ASLA">{{cite web |work=Analysis and Planning: ASLA 2010 Professional Awards | title=Seattle Green Factor |url=https://www.asla.org/2010awards/519.html |publisher=American Society of Landscape Architects |access-date=17 November 2019}}</ref>

By 2010, Seattle was home to approximately {{convert|8.25|acre|ha|abbr=off}} of green roofs.<ref>{{cite web|title=Green Roof Database and Evaluation|url=http://greenfutures.washington.edu/index.php/projects/detail/green-roof-evaluation-and-database|website=Green Futures Research + Design Lab|publisher=University of Washington|access-date=17 November 2019}}</ref> Despite initial hiccups in the city stemming from weeds, lack of irrigation during dry summer months, and a need for continuous replanting, the project has continued to succeed as understanding around the best soils and plants and the need for monitoring and upkeep has increased.<ref name="stiffler" /> A 2010 survey of the green roofs in Seattle acknowledged that while the initial costs of implementing a green roof may deter businesses or homeowners, it is likely that green roofs actually preserve the roofing material and cut costs in the long run.<ref>{{cite web |last1=McIntosh |first1=Annika |title=Green Roofs in Seattle: A Survey of Vegetated Roofs and Rooftop Gardens |url=http://www.seattle.gov/Documents/Departments/OSE/Green-Roofs-In-Seattle.pdf |website=Seattle.gov |publisher=City of Seattle |access-date=17 November 2019}}</ref> In light of the success in Seattle, other cities such as Portland, Chicago, and Washington, D.C. have all made efforts to develop their own Green Factor programs.<ref name="ASLA" />

The Seattle City Hall has led the way by implementing a green roof project that has involved the planting of more than 22,000 pots of sedum, fescue, and grass.<ref name="cityhall">{{cite web |title=Seattle City Hall |url=https://www.greenroofs.com/projects/seattle-city-hall/ |website=Greenroofs.com |access-date=20 November 2019}}</ref> The City hopes that the project can reduce the annual stormwater [[Urban runoff|runoff]] for the building by 50 to 75 percent, which will in turn reduce damage to local watershed areas that provide habitats for native species such as salmon.<ref name="cityhall" /> The historic Union Stables building has used green roofs alongside other [[Efficient energy use|efficiency]] based changes to reduce stormwater runoff and decrease the building's energy use by 70 percent.<ref name="sbm">{{cite web |title=Green Roofs + Seattle's Downtown: A Perfect Match |url=https://www.seattlebusinessmag.com/green/green-roofs-seattle%E2%80%99s-downtown-perfect-match |website=Seattle Business Magazine |access-date=20 November 2019}}</ref> The Park Place building in Seattle's downtown provides a leading example of the use of landscaping to [[Rainwater harvesting|recapture rain water]] with the hopes of cutting back spending on utilities.<ref name="sbm"/>

====Washington, D.C.====

Washington, D.C., started implementing incentives for green roofs within their city at the beginning of the 21st century. In 2003, the Chesapeake Bay Foundation introduced a "green roof demonstration project" in combination with the D.C. Water and Sewer Authority.<ref name=":0">{{Cite web|title=Washington D.C. Green Roof Program {{!}} Adaptation Clearinghouse|url=https://www.adaptationclearinghouse.org/resources/washington-d-c-green-roof-program.html|access-date=2020-12-04|website=www.adaptationclearinghouse.org}}</ref> This program issued grants to several pilot green roofs, which would assist with the cost of construction for the building owner. From this project the city began to understand how beneficial these roofs could be and more programs were implemented over the years. In 2007, the Riversmart Rewards Program introduced a RiverSmart Rooftops Green Roof Rebate Program that would lend a $3 per square foot subsidy to potential green roof projects within the District. This culminated to assist 12 projects that year.<ref name=":0" /> A year later, the subsidy was raised to $5, incentivizing even more developers to use this program within their design. There is also possibility through the RiverSmart Rewards program for "residents and property owners to receive a significant discount on their water utility fees" if they install approved stormwater management features.<ref>{{Cite news|last=Charron|first=David|title=How green roofs can save you lots of green|language=en-US|newspaper=Washington Post|url=https://www.washingtonpost.com/news/where-we-live/wp/2016/03/22/how-green-roofs-can-save-you-lots-of-green/|access-date=2020-12-04|issn=0190-8286}}</ref> In 2016, a rebate of $10-$15 per square feet was introduced, "promoting the voluntary installation of green roofs for the purpose of reducing stormwater runoff and pollutants".<ref name=":2">{{Cite web|title=Green Roofs in the District of Columbia {{!}} ddoe|url=https://doee.dc.gov/greenroofs|access-date=2020-12-04|website=doee.dc.gov}}</ref> $10 per square foot rebates were set for installation within a combined sewer system. $15 per square foot rebates were set for installation within a municipal storm sewer system. The greatest aspect of this incentivized project is the lack of restriction of building type that qualifies. There is no size cap on properties that qualify whether it's residential, commercial or institutional.<ref name=":2" /> In 2016 there was a total of 2.3 million square feet of green roofing within the district. As of 2020, there is 5.1 million square feet of green roofing.<ref>{{Cite web|title=Inventory of Green Roofs {{!}} ddoe|url=https://doee.dc.gov/publication/inventory-green-roofs|access-date=2020-12-04|website=doee.dc.gov}}</ref>

==See also==
{{Portal|Architecture|Environment|Gardening|Water}}
*[[Arcology]]
*[[Blue roof]]
* [[Covering (construction)]]
*[[Ecovillage]]
*[[Energy-efficient landscaping]]
*[[Hanging Gardens of Babylon]]
*[[Low-impact development (U.S. and Canada)|Low-impact development]]
*[[Rainwater harvesting]]
*[[Ralph Hancock (landscape gardener)|Ralph Hancock]], designer, The Rockefeller Center Roof Gardens
*[[Roof garden]]
*[[Sod roof]], traditional roof in Scandinavia
*[[Sustainable city]]
*[[Subtropical climate vegetated roof]]

<ref name="Li2023">{{cite journal
 |last1=Li
 |first1=Y.
 |title=Thermal performance of extensive green roofs: A systematic review and meta-analysis
 |journal=Energy and Buildings
 |date=September 2023
 |volume=296
 |article-number=112642
 |doi=10.1016/j.enbuild.2023.112642
 |url=https://www.sciencedirect.com/science/article/pii/S0378778823005294
|access-date=2 November 2025

}}</ref>

==References==
{{Reflist|30em}}

==Further reading==
*{{cite journal |last1=Hofmann |first1=Michaela M. |last2=Renner |first2=Susanne S. |title=Bee species recorded between 1992 and 2017 from green roofs in Asia, Europe, and North America, with key characteristics and open research questions |journal=Apidologie |date=June 2018 |volume=49 |issue=3 |pages=307–313 |doi=10.1007/s13592-017-0555-x |s2cid=6215743 |doi-access=free |url=https://hal.archives-ouvertes.fr/hal-02973379/file/springer.pdf }}
*Snodgrass, E. and McIntyre, L., ''The Green Roof Manual: A Professional Guide to Design, Installation, and Maintenance'' Publisher: Timber Press (2010).
*Dunnett, N. and Kingsbury, N., ''Planting Green Roofs and Living Walls'' Publisher: Timber Press (updated 2008).
*Miller-Klein, Jan. ''Gardening for Butterflies, Bees and other beneficial insects'' {{ISBN|978-0-9555288-0-4}} has large section on green and brown roofs and brownfields, including how to make your own, with contributions from several UK practitioners.
*{{cite journal | last1 = Scholz-Barth | first1 = Katrin | year = 2005 | title = Harvesting $ from Green Roofs: Green Roofs Present a Unique Business Opportunity with Tangible Benefits for Developers | journal = Urban Land | volume = 64 | issue = 6| pages = 83–87 |url=http://www.roofmeadow.com/wp-content/uploads/Harvesting__From_GR.pdf }}
*Hilary, David. ''Creating My Green Roof: A guide to planning, installing, and maintaining a beautiful, energy-saving green roof.'' {{ISBN|978-1-4783-6807-6}} (2015).
*Roland Appl, Reimer Meier, Wolfgang Ansel: ''Green Roofs – Bringing Nature Back to Town''. (Proceedings) Publisher: International Green Roof Association IGRA, {{ISBN|978-3-9812978-1-2}} (2009)
*Diversity of Fauna on Green Roofs  [https://web.archive.org/web/20120319200626/http://www.greenroofs.org/grtok/materials_browse.php?id=59&what=view Diversity of fauna]

==External links==
* {{Commons category-inline|Green roofs (sustainability)}}
* [http://asla.org/2009awards/050.html  ASLA Design Award 2009: CALIFORNIA ACADEMY OF SCIENCE]

{{Roofs}}
{{Stormwater structures}}
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[[Category:Roof gardens]]
[[Category:Roofs]]
[[Category:Sustainable architecture]]
[[Category:Sustainable gardening]]
[[Category:Sustainable building]]
[[Category:Garden features]]
[[Category:Types of garden]]
[[Category:Landscape architecture]]
[[Category:Urban agriculture]]
[[Category:Hydrology and urban planning]]
[[Category:Environmental engineering]]
[[Category:Roofing materials]]
[[Category:Climate change adaptation]]

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