Green roofs are a term commonly used to describe roofs covered with vegetation.
The term includes a wide range of solution, from a thin layer of sedum plants to parks on roofs with bushes and trees. Using plants on ceilings can be traced far back in human history. The most well-known example is the “Babylon’s Hanging Gardens”, one of the seven wonders of ancient times. In the north, green roofs have a long tradition on many Scandinavian buildings but disappeared from the towns during the 19th century. It was not until the end of the 20th century that green roofs became popular. Now they are widely used as a method for a sustainable and more climate adapted urban development.
Green roof benefits
There are many benefits from green roofs, especially in an dense urban setting.
The ecological benefits of green roofs are that they create conditions for a richer flora and fauna in the city and thus have a positive impact on biodiversity. It is possible to replicate natural habitats on the roof with plant communities that have not previously existed in the city. Common animals on green roofs are various invertebrates and important bees, such as bumble bees, bees, spiders, butterflies, beetles and hoverflies, as well as some birds.
Another important benefit of green roofs is how it reduces urban runoff. By planting vegetation on the roof, a significant amount of water will be absorbed by the vegetation and substrate. The total reduction is between 40 – 90 % depending on the substrate depth, the slope and size of the roof and what season it is. In addition, the water runoff from the roof is always a bit delayed which reduces the pressure on the urban drainage systems.
Green Roofs helps to reduce Urban Heat Islands which occur because dense cities with a lot of concrete and asphalt absorbs a lot of the heat from the sun. Green roofs have better albedo than black or grey roofs and furthermore the evapotranspiration from the plant bed and vegetation keeps the roof cooler. Green Roofs also expand the life expectancy of the water proofing membrane that is located under the green roof system. This is due to less fluctuations in temperature, decreased surface temperature and UV radiation. The life expectancy is difficult to calculate in an exact figure but can be estimated to between 25 – 50 % depending on water proofing membrane solution and green roof solution.
Read about more benefits
Read more about green roofs in this manual on green roofs that shows the whole process - from vegetation to waterproofing and everything in between. Read online or download the manual. We at the Green Institute were one of the project partners who participated in the development of the handbook.
The Scandinavian Green Infrastructure Association (SGIA) is a non-profit organisation with members from academia, municipal departments, green roof entrepreneurs, architects, developers and other organisations with an interest in green roofs and urban green infrastructure.
Interested in what’s happening with green roof and green infrastructure development? The SGR Institute newsletter is sent in English 2 times a year, where we keep you updated on the development in Scandinavia. You’re welcome to sign up to our mailing list!
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