What is a green roof?

The term includes a wide range of solutions, 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

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.

Urban runoff

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.

Temperature

A green roof reflects more sun rays than roofs with dark waterproofing and evaporation from green roofs also contributes to lower surface temperatures. It can in some cases have a positive impact on the need for air conditioning inside the building and the city's climate. A common roof sealing layer is often vulnerable to UV light and rapid temperature changes. A green roof protects the sealing layer and extends its life considerably.

Health and well-being

Several studies show that we humans feel better when we have a lot of greenery around us. Green roofs are a way to increase the vegetation on surfaces that are otherwise usually hard and gray. Being able to look out on a green roof or using roofs for parks and gardens has a calming and health-promoting effect. The green roof's plant bed and vegetation also reduce the noise level, which also contributes to increased well-being. The noise-canceling effect increases the deeper the plant bed is.

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.

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