Replace Parliament's lawn with flowers, expert recommends
Going native ... how Parliament House might look covered in native flowers. Illustration: Marco Mana
Parliament House in Canberra could slash its carbon footprint by replacing its "water and energy intensive" turf roof with native succulents such as pigface, flax lilies and alpine wildflowers from the Snowy Mountains, according to a green roofs expert.
New research has shown a living green roof using a mix of Australian plants can cut a building's summer heat gain by up to 24 degrees, reducing air conditioning use and greenhouse emissions, according to new research.
The University of Queensland study found a green roof using drought-tolerant native plants can also cut stormwater runoff by up to 60 per cent, improve air quality, reduce noise pollution and provide food and shelter for native birds and insects.
South Australian architect Graeme Hopkins - one of Australia's top experts on green roofs and walls - said the iconic roof of parliament sould be a swathe of bright yellow billy buttons, livening up the vista, as well as providing urban wildlife habitat.
"People will often point to Parliament House as an example of a green roof, but it's not," Mr Hopkins says.
"It's an out-dated symbol of our love affair with the English lawn, and the social status it once conveyed. We'd do better to rip it out and put in a native grassland. You could have a wonderful mix of colours."
The research, funded and published by the federal government's Rural Industries Research and Development Corporation, tested a variety of native plants that could be used to green-up the roofs and walls of commercial buildings. Most green roofs in Europe and North American make extensive use of sedums - a hardy succulent - but they are not suited to Australia's humid sub-tropics or Canberra's semi-arid climate.
"Sedums will work in Sydney or Brisbane, but not in hot dry conditions. They tend to collapse under heat," Mr Hopkins says.
He points out there's also often confusion between roof gardens and green roof. A rooftop garden is usually designed " more with aesthetics and recreation in mind," but a green roof is structure designed to deliver maximum environmental benefits. Green roofs and walls are also designed to use a lighter planting medium than soil.
"The basic difference is a green roof covers the entire roof area, whereas a rooftop garden has garden beds on parts of the roof. If you tried cover an entire roof surface with a normal garden bed, it would would be far too heavy - the roof would collapse under the weight."
Green roofs have taken off in the United States - Chicago has more than 500 - but uptake in Australia has been hampered by the search for suitable native species. And there's also the added issue of potential fire risk - or fire management. Mr Hopkins says one option for Parliament House could be a native grassland featuring a mix of kangaroo and wallaby grasses.
"But those grasses need fire to regenerate. A control burn on the roof of Parliament House might not be such a good idea."