The Value of Living Roofs
Green roofs are covered in living vegetation, built on top of a growing medium, as well as a waterproof layer. Living roofs are often made particularly for wildlife. They are valued for their environmental advantages, giving important ‘green space’ to urban areas, therefore benefitting wildlife, as well as providing services to people.
The layer of living material gives the roof increased insulation, allowing for building temperatures to be regulated. This means less energy is wasted, so less fossil fuel needs to be used. They also influence rainfall runoff as the living layer on the roof will intercept and absorb some of the rainfall, even helping to reduce flooding issues in some areas as the rain would not run-off impermeable concrete surfaces all at once. Vegetation composition does however influence how much rain stays in the system (Dunnett et al, 2008), with the substrate depth, size and age of the roof affecting plant diversity (Madre et al, 2014). Therefore living roofs can play a part in regulating rainfall runoff as well as temperature, as evaporation occurs from the living roof layer creating a cooling effect, helping to keep buildings cool in summer.
As well as providing benefits for humans, such as pleasing aesthetics or reduced energy bills, living roofs also provide benefits for wildlife. Studies in New York City showed that there was more bat activity over buildings that had green roofs than without (Parkins and Clark, 2015). Living roofs are becoming more common across the UK and Buglife has started a ‘Living Roofs for London’s Wildlife’ scheme, which aims to have living roofs built in London with vegetation species that will benefit insects. Therefore living roofs could provide benefits for various pollinating insects, such as the Brown-banded carder bee which is an endangered species. Studies have shown a variety of insect species in varying numbers recorded on living roofs in London as well as some scarce species (Kadas, 2006). The habitat on the rooftop can however be harsh, causing a unique environment to develop. A report by English Nature (Jones, 2002), which surveyed eight London green roofs, recorded 136 invertebrate species. Although this was classified as a comparatively poor amount, some species were recorded that were not usually in the area because of the conditions the roof top habitat was providing, such as beetles which would otherwise be found in gravel pits. Roofs can also benefit birds and can be tailored for a specific species, such as the black redstart.
If a building is large enough the expanse of living roof can be likened to a park, creating a resource reachable by birds and flying insects. However, habitat at ground level, which has not been destroyed or removed, is extremely valuable, so living roofs should not be used as compensation methods without thinking about the implications. Roofs are also ‘islands’ in amongst, in many cases, a hostile urban environment but in areas already dominated by buildings they are a valuable tool which can help increase sustainability and produce an area for wildlife. Although they are expensive they can help reduce heating and air conditioning costs for the owner of the building in the long-term as well as benefiting wildlife along the way.
Dunnett, N., Nagase, A., Booth, R. and Grime, P. (2008) ‘Influence of vegetation composition on runoff in two simulated green roof experiments’, Urban Ecosystems, 11, 385-398.
Jones, R. (2002) Tecticolous Invertebrates: A preliminary investigation of the invertebrate fauna on green roofs in urban London. London: English Nature.
Kadas, G. (2006) ‘Rare invertebrates colonizing green roofs in London’, Urban Habitats [online]. (Accessed 04/11/2015). www.urbanhabitats.org/v04n01/invertebrates_full.html
Madre, F., Vergnes, A., Machon, N. and Clergeau, P. (2014) ‘Green roofs as habitats for wild plant species in urban landscapes: First insights from a large-scale sampling’, Landscape and Urban Planning, 122, 100-107.
Parkins, K. and Clark, J. (2015) ‘Green roofs provide habitat for urban bats’, Global Ecology and Conservation, 4, 349-357.
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