Growing a Green Roof
[ The University of Melbourne Voice Vol. 3, No. 6
11 August - 8 September 2008 ] By Nerissa Hannink
Research into the suitability of Australian native plants for ‘green roofs’ is under way at the University of Melbourne’s Burnley campus.
Green roofs – shallow rooftop gardens – are becoming increasingly popular internationally for their environmental and energy saving benefits.
“Green roofs have amazing potential but have not yet been evaluated under Australian climatic conditions,” says project leader and Burnley campus lecturer Dr Nick Williams.
“We are examining the suitability of selected native plants for green roofs by measuring their survival, growth rate and response to drought stress.”
Dr Williams says green roofs (defined as roofs which support planted vegetation) have demonstrated benefits. They can reduce run-off of roof water, offer aesthetically pleasing cityscapes, lengthen roof life, significantly reduce building energy use and reduce the urban heat island effect.
“A Canadian study found that a green roof reduced daily energy use during summer by 75-90 per cent compared with a control roof,’ he says.
“The installation of green roofs could therefore form an important adaptive response to climate change by directly and indirectly reducing the energy demands of urban buildings.”
Green roofs are established by installing a waterproof membrane, followed by a root barrier, a cellular plastic drainage layer and a specifically designed lightweight growing media.
Co-researcher and Burnley lecturer John Rayners, says the project will establish an experimental green roof and monitor its effect on roof temperatures and the building energy budget by comparing it with an otherwise identical control roof.
“Green roof plants used overseas are typically from arid, mountainous or coastal environments. Plants need to be robust and low in height so that they don’t get blown off the roof, and need to have good drought tolerance, like exposure to full sun and be easily maintained.
“We have selected a range of Australian and exotic species to trial that meet these criteria including herbs and grasses that grow in the native grasslands west of Melbourne and succulents from arid inland regions,” he says.
The research will be used to provide information to architects, landscape designers and public policy-makers who wish to install green roofs suitable for Australian conditions and objectively evaluate the environmental benefits.
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