A roofing answer to climate change

Last month in the Sydney Morning Herald, controversial property tycoon Harry Triguboff challenged Australian cities to have more buildings and fewer trees.

As any urban planner knows, parks and greenery in cities and towns are vital “lungs” for air purification. They are all restful to the burdened soul.

But if he’s serious, rather than despising Harry's penthouse-and-pavement sentiments, we should suggest that Harry has his cake and eats it too.

Green roof technology has been around for years. However, most Australian property developers (including Harry), architects, planners, horticulturalists and building owners are yet to capitalise on significant profit prospects posed by the aesthetic, environmental and fiscal benefits of putting gardens on our roofs.

Already, Europe has developed green roof technology to a high level of cost-efficiency and positive environmental impact, while North American municipal governments, especially in Toronto, Chicago and New York, are also discovering financial and environmental benefits from well-engineered rooftop gardens (New York's Rockefeller Centre is a landmark example).

With the threat of global warming, green roofs provide reduction of ambient temperatures in cities, caused by the “heat island effect” of buildings and roads. A study released early this year in Toronto showed that green roof technology can reap huge cost savings for building owners and the community.

A key finding was that an 8 per cent cover of green roofs over the city would reduce the city’s heat island effect by up to 2C.

Rapid urbanisation around the world has meant that heat island effects of cities are becoming significant contributors to global warming. Compared with nearby rural areas, a city’s ambient temperature can be from 6 to 10C warmer because of heat absorbed and then released from roadways and buildings.

Cr Joe Pantalone, Deputy Mayor of the City of Toronto, said the study of the benefits of green roofs to Toronto also included direct energy savings of C$12 million a year in buildings from reduced cooling demand in summer.

Would a saving of this magnitude attract developers like Harry Trugiboff?

Cr Pantalone said savings also included indirect city-savings at peak load demand of C$80 million a year. Plus it meant reduced levels of carbon dioxide, nitrous oxide, ozone and PM10 particulates and sulphur dioxide from reduction of heat island effects and the trapping of gases and particulates by plants grown on green roofs.

Importantly for Australia, it meant reduction of stormwater flows by 12 million cubic metres a year, so that existing drainage infrastructure can cope, and sewage overflow events were less frequent. This also makes good economic sense: Cr Pantalone said Toronto’s savings were C$79 million a year from reduced capital costs for storm-water management, erosion control and sewer overflows.