BANNER: Building Greener - A project managed by CIRIA
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The implementation of green roofs, green walls and complementary features can make a significant contribution to meeting the challenge of sustainable development by:

Wider environmental and social benefits also result from the implementation of green roofs, green walls and complementary features, including potential improvements in amenity and health (psychological and physiological).

Biodiversity in urban areas

Urban areas are important for wildlife. Gardens, parks and other urban green spaces often have high biodiversity value and brownfield sites can play host to rare plants and invertebrates. However, modern building techniques, with their tendency towards clean architectural lines and the use of hard wearing and impermeable materials, have inevitably limited the opportunities for wildlife to colonise the built environment. At the same time, the regeneration of urban areas has seen the redevelopment of much brownfield land.

In order to conserve and enhance biodiversity it is important that a variety and matrix of habitats are provided. There is enormous potential for green roofs, green walls and complementary features to provide new nesting and foraging habitat for a wide variety of species, and to connect existing urban green spaces.

Stormwater management in urban areas

When a site is developed, impermeable surfaces and artificial piped-drainage systems are introduced. As a result, natural drainage patterns are disrupted and surface water run-off increases, with a resulting increase in downstream flood risk. Green roofs can help prevent this happening, when introduced as a source control technique within a well designed sustainable drainage system (SUDS).

The SUDS philosophy is to replicate the natural drainage patterns as closely as possible. Green roofs have the potential to store rainwater in their substrate and, to a lesser extent, in and on the plants that grow on them, before it is evaporated or transpired back into the atmosphere. The contribution that green roofs can make to stormwater management has been a major driver for their use both in the UK and overseas.

Climate change mitigation and adaptation

Buildings being constructed today will have to accommodate possible climate change impacts over their lifetimes. Likewise, existing buildings will need to be adapted to allow for forecast climate change. The use of green roofs and green walls could potentially play an important role in mitigating the effects of buildings on the climate, and also helping to adapt buildings to changes in climate. Green roofs and walls can contribute in the following ways:

Green roofs and energy transfer – the insulating effect of a green roof can help to reduce the transfer of heat between the external and internal environment or vice versa. This can reduce internal heating and cooling costs.

Green walls and surface temperature – during the summer green walls can reduce the surface temperature of the wall through evapotranspiration and shading. In the winter green walls can reduce the cooling effects of wind, rain and snow on the surface temperature of the wall.

The urban heat island effect – the reduction in roof and wall surface temperatures can help to reduce the impacts of the urban heat island effect, which is likely to be increasingly significant in a warming climate.