page_title: Green roof
section_title: History
hierarchical_section_title: Green roof / History
caption_attribution_description: Authentic Viking recreation, Newfoundland, CanadaJuly 17 - 30, 2003
context_page_description: A green roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage and irrigation systems. Container gardens on roofs, where plants are maintained in pots, are not generally considered to be true green roofs, although this is debated. Rooftop ponds are another form of green roofs which are used to treat greywater. Vegetation, soil, drainage layer, roof barrier and irrigation system constitute green roof.
  Green roofs serve several purposes for a building, such as absorbing rainwater, providing insulation, creating a habitat for wildlife, increasing benevolence and decreasing stress of the people around the roof by providing a more aesthetically pleasing landscape, and helping to lower urban air temperatures and mitigate the heat island effect. Green roofs are suitable for retrofit or redevelopment projects as well as new buildings and can be installed on small garages or larger industrial, commercial and municipal buildings.
context_section_description: 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.
  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".
  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. Germany was the first country to start developing green roof systems and market them on a large scale. The City of Linz in Austria has been paying developers to install green roofs since 1983, and in Switzerland it has been a federal law since the late 1990s.  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
  Rooftop water purification is also being implemented in green roofs.  These forms of green roofs are actually treatment ponds built into the rooftops.  They are built either from a simple substrate (as being done in Dongtan) or with plant-based ponds (as being done by WaterWorks UK Grow System and Waterzuiveren.be Plants used include calamus, Menyanthes trifoliata, Mentha aquatica, etc.)
  Several studies have been carried out in Germany since the 1970s. 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".
caption: Re-creation of Viking houses in Newfoundland
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