In times past, spreads of bountiful grass and plants on the roof of buildings were considered to be flights of fancy of avant-garde architects. However, due to a multitude of environmental, social and economic benefits, green roofs are now moving into the mainstream in the UK and worldwide.
Green roofs are defined as any roof structure topped with a layer of soil and plants. The definition is broad – green roofs can stand for anything from a thin layer of turf to lovingly sculpted landscapes such as the one atop the Steinhaus Rogner Bad Blumau in Austria1. Green roofs used to be widespread before the industrial revolution; however they only came back into fashion after the Second World War. Germany proved to be the pioneers of this technology – in the 70s local councils started to incorporate green roof construction requirements into research and policy and by the early 2000s, 43% of German cities provided incentives for the construction of green roofs. Now, in Munich all flat roof spaces of over 100 square metres are obliged to have a green roof.
Now interest in these innovations has spread around the world2. In Copenhagen all roofs with a slope of less than 30° are required to install green roofs. The Singapore Government provides technical assistance and grants to developers in order to meet an ambitious target to create 50 hectares of ‘Skyrise Greenery Areas’ by 2030. The UK has been behind the curve in terms of green roof policy, but recently there have been signs that this is changing. Sheffield city council now expects large developments to include green roofs within new planning applications and they are now strongly encouraged in London, with a target of 5% green cover for the city by 20303,4.
So why has there been such a resurgence of interest in green roofs in recent times? Only recently, researchers and planners have realised the environmental, social and even economic benefits of green roofs, which we explain one by one below5,6.
1. Increasing air quality
Plants can reduce the amount of polluting air particles, such as heavy metals and volatile organic compounds from the city’s atmosphere, resulting in fresher, cleaner air. Plants also take up the greenhouse gas carbon dioxide from the atmosphere, reducing the impacts of climate change.
2. Increasing biodiversity of wildlife
If carefully designed with a thick (> 80 mm) soil depth and using species of plants or grass suitable to the local area, green roofs can maintain and increase biodiversity of plants and insects in habitat-deprived city centres.
3. Reducing the heat island effect
Roofs and roads are dark and so absorb more heat from the sun than green areas. This leads to an increased temperature of several degrees C within cities compared to the surrounding countryside, known as the ‘heat island’ effect. Green roofs can counter this effect by reflecting more of the sun’s rays (due to their lighter green colouring) and by shading and insulating the underlying roof structure. Additionally, evaporation of water from the soil and plants can cool the roof further. Overall, green roofs can lead to a fresher, cooler city.
4. Increasing energy conservation
Green roofs can lower your energy bills by increasing the roof insulation of the buildings they are placed upon. This can reduce the overheating of under-roof spaces of buildings in summer (meaning that less air conditioning needed) and the heat lost through roofs in winter (leading to a lower heating requirement). Find out about other ways to insulate your home.
5. Increasing green space and roof accessibility
In many city centres, the accessibility of green spaces is severely limited. If opened to the public, green roofs can provide a way for people to have increased access to green spaces and wildlife. And who doesn’t like a garden with a view?!
6. Reducing flooding
Conventional roofs are designed to allow rainwater to flow immediately into the drainage system. In severe storms, the sudden rush of water to the drainage systems across a city can lead to overflowing pipes and flooding. The soil and plants on green roofs can hold onto water for a longer amount of time, releasing it slowly into drainage systems over several hours and so reducing the risk of flooding.
7. Increasing the value of buildings and reducing the cost of energy
Green roofs could even save you money7. By reducing air conditioning costs in summer and heating costs in winter (as mentioned in number 4, above), it’s been estimated that green roofs can substantially reduce energy costs over the whole year7. Secondly, by adding ‘green credentials’ to their project, some landlords have found that business tenants are more likely to ask to move in and the value of the property may be increased.
Despite all the benefits, green roofs do come with some downsides. They have to be designed carefully to maximise potential benefits; for example by using thick soils (> 80 mm) and native plants. Also, there are costs associated with the installation and maintenance of such technologies. However, despite the downsides, advocates and a growing number of local authorities across the UK, Europe and the world believe that the benefits of green roofs are worth the asking price. So next time you’re thinking of a unique way to brighten up your rafters, or if you’re redeveloping a building and need a fresh idea, why not give green roofs a try? For more information on their history, design and construction take a look at the references below.
References:
1. Green Business Watch. Amazing green roof images. 2013. Available at: http://greenbusinesswatch.org/blog/green-roof-images. Accessed April 23, 2013.
2. International Green Roof Association. 2013. Available at: http://www.igra-world.com/.
3. Greater London Authority. Greening roofs and walls. 2013. Available at: http://www.london.gov.uk/priorities/environment/greening-london/urban-greening/greening-roofs-and-walls.
4. Sheffield City Council. 4 Guideline DES1: Green Roofs.; 2013. Available at: http://sheffield-consult.limehouse.co.uk/portal/spd/designing_for_environmental_sustainability?pointId=d3671818e159.
5. Livingroofs.org. 2013. Available at: www.livingroofs.org.
6. Groundwork Sheffield. The Green Roof Guide. 2011. Available at: www.greenroofguide.co.uk.
7. Groundwork Sheffield. Green Roof Developer’s Guide.; 2011. Available at: http://www.greenroofguide.co.uk/downloads/dev_guide_v3.pdf.
