No space for green in cities
Most cities in the world share one common problem: a lack of green spaces. Some do better in terms of parks and trees than others, but mostly cities consist of concrete plastered over enormous amounts of area. Globally, around 580,000 km² fall under the category of being such a concrete-plastered area. As established by the National Oceanic and Atmospheric Administration (NOAA), this is the amount of total impervious surface area in the world, which includes features created by man such as roads, buildings, parking spaces, pedestrian paths, driveways and similar structures. [1]
Living roofs or green roofs
While many of these structures and their appeal can be considered a matter of taste, roofs of buildings in particular are often space that goes unused. Apart from the obvious function of providing shelter, they often fulfill no other function where they could have so many. One of them is made use of by establishing living roofs, also called green roofs.
In short, green roofs are roofs that have been planted with grass, trees, vegetable gardens or any other kind of vegetation. As an increasing amount of surface area is sealed by human infrastructure, ecosystems are negatively affected, habitat is lost for both flora and fauna species, and natural balances are destroyed. When roofs are vegetated, some of these negative effects can be alleviated. [2]
Living roof structure
Living roofs can be an extension of existing roofs, or included in newly built structures. They usually consist of a structural support system, a layer that controls vapourisation, possibly insulation, a waterproof layer on top of this, plus a layer for drainage, and, of course, one layer of soil or similar growing material to sustain the plants. This system allows for growth of lawn, trees, vegetables or really any other plants. It is possible to create an urban green landscape on top of virtually any building. Important for this are good water proofing and a lightweight medium for plants to grow in. [3]
Function and effects of living roofs
Living roofs can function as natural insulation and thus contribute to a reduction in costs for heating and cooling of buildings. They also support cooling through natural evaporation and transpiration processes of plants and soil. Living roofs can, moreover protect roofs from weather damage, extending their life span by two to three times. [4]
In environmental terms, planted roofs can be helpful to enhance biodiversity and provide additional habitats which are rare in urban environments. They absorb and deflect sound and thereby contribute to a reduction in noise, which can be particularly beneficial in noisy areas such as the surrounds of airports or motorways. Furthermore these living roofs help with a moderation in air temperature, which can have a positive effect in cities where for example sealed surfaces lead to an increased temperature on hot days. Lastly, green roofs also work to improve air and water quality, and can even be used - in form of a wetland system for example - to filter water to be used in the building. [4]
Environmental, social and economic benefits
These and many more functions of living roofs lead to the fact that they provide a city and its people with environmental, social and economic benefits. The roofs break up urban areas just like parks and lakes do, providing spaces of recreation that can be used for leisure activities as much as to grow vegetables of flowers. They can improve both working and living environments and contribute to the overall health of urban ecosystems as much as human health.
Sources
[1] Elvidge et al. (2007), Global Distribution and Density of Constructed Impervious Surfaces, NOAA Full Research Paper, http://www.ngdc.noaa.gov/dmsp/pubs/ISAglobal_20070921-1.pdf
[2] International Green Roof Association IGRA, www.igra-world.com
[3] Green Roofs for Healthy Cities, Green Roof Infrastructure Industry Association, www.greenroofs.org
[4] Living Roofs New Zealand, www.livingroofs.org.nz
Hannah Mueller - Strive to expand your knowledge every day. Hannah is a young environmental professional based in New Zealand.
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