Living roofs play an important role in helping to achieve London’s target to increase green cover in central London by 5% by 2030. They can improve the city’s resilience to the impacts of climate change by reducing the amount and speed of storm water run-off and helping to keep buildings, and the surrounding areas, cooler during increasingly frequent hot spells. They also provide much needed outdoor living space, improving life for both residents and adding to the beauty of the local neighbourhood.
The illustrated publication, City of London green roof case studies provided to the City of London Corporation includes a number of green roof applications in The City describing their context, format, drivers, barriers, benefits and notes on biodiversity.
It is estimate that there are around 700 green roofs in central London alone, shown on the map below. New green roofs need to be built to meet the greening targets, installed through both new development proposals and through the retrofit of existing buildings, to deliver as many of the following objectives as possible:
- Reduction of Urban Heat Island – Research in Tyndale Centre for climate change suggests we need a 10% increase in green space in our cities to combat climate change. This is particularly relevant to the reduction in the Urban Heat Island [UHIE]. Green roofs are recognized to have a positive effect on reducing the UHIE
- Biodiversity – Green roofs can provide important refuges for wildlife in urban areas. Research in Switzerland and the UK has demonstrated that green roofs can provide important refuges for rare invertebrate populations.
- Water – Green roofs can significantly reduce the surface run off volumes and rates of rainfall leaving roofs. As a source control mechanism in the Sustainable Urban Drainage System green roofs can help reduce flash floods as a consequence of intense rainfall events. This will become increasingly important as a consequence of climate change. Green roofs also improve the quality of water and although the amount of water is reduced it is possible to rainfall harvest from roofs that have been greened.
- Thermal Performance – Green roofs cannot be given a U-value at present. However they have been shown to significantly reduce the need for air conditioning in summer and can provide a degree of insulation in winter.
- Sound Insulation – The combination of soil, plants and trapped layers of air within green roof systems can act as a sound insulation barrier. Sound waves are absorbed, reflected or deflected. The growing medium tends to block lower sound frequencies whilst the plants block higher frequencies.
- Protection of Waterproofing – The original green roofs in Germany stem from covering wet bitumen with 6cm of sand, which became vegetated. This covering was to protect the wet bitumen from fire. Green roofs have now been shown to double if not triple the life of waterproofing membranes beneath the green roof.
- Air Quality – airborne particles and pollutants are filtered from the atmosphere by the substrates and vegetation on a green roof.
- Amenity Space – in dense urban environments there is often a lack of green space for residents. Roof Gardens and roof top parks provide important green spaces to improve the quality of life for urban residents.
- Urban Agriculture – in the form of Urban Rooftop Food Growing – roofs, where strong enough provide a space for urban food growing. Although many large flat roofs may not have the loading capabilities to hold food growing some roofs will and the many balconies in are urban areas are ideal.
Transport for London have installed green roofs at St James’s tube station and West Ham bus garage and a green wall at Edgware Road tube station.
This green roof map of London below shows there are around 700 green roofs in central London alone, covering an area of over 175,000m2. That’s 17.5 hectares or around 25 football pitches. The green roof map was produced by the GLA and the Green Roof Consultancy by studying aerial images of London taken in 2013 (by The Geoinformation Group).
The map currently contains 678 known green roofs, but there are many which are missing, including those that have been installed since the summer of 2013. If you would like us to add a green roof to the map please email, GIMap@london.gov.uk. Or, if you would like to add more information about a green roof currently on the map – such as a photo, or links to a website with further details of the roof – then please click on the green roof on the map and the ‘email us’ link, which will open a new email window
Image sources: City of London Corporation