Green Roofs Turn Cities Upside Down: As Urban Density Increases, Green Roof and Wall Technology Is Evolving Fast. It Provides a Way to Replace Vegetation Lost on the Ground as Well as a Host of Energy, Water Management and Aesthetic Benefits

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Imagine flying into an Australian city where instead of the traditional sprawl of rooftops, buildings are covered by a blanket of green. Such a scenario may be some way off but green roofs are appearing on commercial and residential buildings as people start recognising their potential to moderate the effects of global warming.

Green roofs range from those that have a simple covering of grass--such as Australia's parliament house--to the 'bushtop' systems being developed in Adelaide which include biodiversity as well as significant insulation and stormwater management benefits.

Sidonie Carpenter, President of Green Roofs Australia and owner of the Brisbane-based green roof and green wall consultancy Green Canopy, has recently returned from the first meeting of the World Green Roof Infrastructure Network (WGRIN) (1) in the United States.

She says that while green roof technologies have developed in other parts of the world over the last 30 years, Australia is rapidly catching up.

'It is exciting to see green roofs being embraced as a way of dealing with climate change, but daunting because we don't have a deep sense of the specific skills required,' she says.

Germany is viewed as the world leader in green roof technology, with some 60 years' experience in design and construction and whole suburban developments covered by green roofs. Other European countries, such as Iceland, Norway and France, also have very strong green roof industries.

In North America, green roofs have been on the scene for the last 10 to 15 years. Toronto has more than 100 green roofs and an incentive scheme to encourage their construction. Chicago, with more than 300 green roofs, also has a policy to encourage their inclusion in new developments.

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In Asia, Japan is the leader in green roof technology with some innovative examples, such as the Roppongi Hills building in Tokyo where a rice paddy on the sixth floor, planted by local school children, produces 60 kilograms of rice per year. It also has an organic vegetable plot, a breeding colony of frogs in the water feature and a barbecue area for corporate functions.

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In Australia, as more architects, urban planners and developers and their clients start demanding buildings that are more energy efficient, the idea of incorporating rooftop gardens and greenery on walls is becoming more common.

Benefits of green roofs include thermal insulation, which reduces energy use in heating and cooling. For a multi-storey building, this energy saving is about 10 per cent and for a single storey building it is 20 per cent, says Adelaide architect, landscape architect and 'bushtop' pioneer, Graeme Hopkins.

Stormwater management is a major driver for green roofs in North America and Europe and something which is becoming increasingly important in Australian cities.

Research is being carried out by Monash University and Melbourne Water on the benefits of green roofs for stormwater management.

Green roofs also reduce the 'heat island' effect in cities by lowering the temperature of the building surface and thus the ambient temperature. The City of Toronto estimates that eight per cent of green-roofed buildings will reduce the temperature by about 2[degrees]C.

Another benefit is cleaner air from plants trapping harmful particulates and dust. Also, solar panels have been found to work more efficiently on green roofs than on a normal roof surface because of the lower surface temperature.

Benefits can be extended from the rooftop to the sides of the building by green or living walls, where plants are grown onto a vertical system, based on principles of hydroponics for moisture and nutrients.

Graeme Hopkins is trialling the suitability of various native plants, such as grasses, sedges and saltbush, in living walls at his Adelaide Hills home and office. …