Green roofs can:
- Help maintain pre-development or greenfield run-off volumes and rates from development sites.
- Improve biodiversity on all new development sites.
- Help ensure that developments are designed to adapt to climate change.
- Help improve the quality of water/run-off.
There are also benefits for the developer and their team:
- Civil and Mechanical Engineers will be able to use the green roof in run-off calculations and reduce the need for air conditioning.
- Landscape and Ecology Consultants can mitigate impacts and improve the development for ecology.
- The cost of the green roof can be balanced with savings in other areas, such as ground-level storm water solutions and energy demand.
A green roof
Environmental benefits
Adapting to climate change
‘Summers by 2050 will be 1.5–3.5oc hotter. In central London the urban heat island currently adds 5-6oc to summer night-time temperatures and will intensify in the future.’ From London’s Warming: The Impacts of Climate Change
- In the UK, the Tyndall Centre for Climate Change has found that an urban area will need to increase the amount of vegetation by 10 per cent to combat climate change. In the majority of our cities there is limited space at ground level for vegetation and soil, so green roofs are an ideal solution.
- It is expected that rainfall patterns will change, leading to more short intensive rainfall events, especially in summer. This will lead to an increase in local flash flooding – green roofs can help reduce this.
Balancing energy and CO2
Green roofs have a substantial thermal mass and so can provide moderate insulation - this means that air conditioning costs can be significantly reduced. Modelling of buildings in Toronto by Environment Canada suggest that 4.15kW/hrs/m2/yr can be saved in reduced air conditioning costs, thus reducing CO2 emissions.
- In London a good example of energy saving is Paradise Park in the London Borough of Islington. Due to the thermal mass of the green roof, no air conditioning has been installed. This has led to a reduction in 3,800kW/hrs and a saving of 1.6 CO2 tonnes.
- Evidence from Germany suggests that green roofs can reduce winter fuel consumption by between 6 –kWh/m2/yr. This depends on how wet the roofs are as this reduces their insulation value.
- Green roofs work well with solar panels, as they increase the efficiency of solar panels by regulating temperature.
For more information, visit LivingRoofs.org's pages on energy conservation and urban heat islands.
Water
- Green roofs reduce the peak flow and the total volume discharged from a roof (they can intercept at least 5mm of rainfall).
- Green roofs can improve the water quality of the run-off. Research in a number of countries has shown that both nitrogen and phosphorus in run-off can be reduced.
For more information, visit LivingRoofs.org's pages on storm water.
Biodiversity
Green roofs provide a habitat for wildlife, especially if you include nest boxes, logs and water features, and plant native species. - Research in London and Basel has shown that well-designed extensive green roofs can provide an important refuge for rare invertebrates associated with brownfield sites and other dry, well-drained, low-nutrient habitats.
- They are an important habitat for rare bird species, especially the Black Redstart in the London area.
For more information, visit LivingRoofs.org's pages on biodiversity.
Other benefits
- Noise entering the building can be reduced by up to 18 decibels. Reflective noise can be reduced by three decibels or more. For more information, visit LivingRoofs.org's pages on noise and sound insulation.
- Green roofs can filter dust and other air pollutants. For more information, visit LivingRoofs.org's pages on air quality.
- They can increase amenity space. For more information, visit LivingRoofs.org's pages on green space and health.
- They improve the property’s value.
- They increase the life of waterproofing by acting as a protective layer against frost, ultra-violet light and other climatic stresses. For more information, visit LivingRoofs.org's pages on extended roof life.
