Green roofs are environmentally friendly and are designed to help keep homes cool in the summer

On the hotter days of the year, most Sydney rooftops will reach 50 degrees and above, says Dr. Peter Irga, Atmospheric Scientist at the Faculty of Engineering, University of Technology Sydney.


A green roof about four to six inches deep with soil, plants and a growth mat can lower surface temperatures by up to 20 degrees, a study by Irga and colleagues Fraser Torpy and Robert Fleck found.

They compared two rooftops in Sydney’s Barangaroo over a year. One had solar panels and was also planted with 15 different native species that bloomed at different times of the year. The other only had solar panels.

Irga says that a green roof cools the roof temperature and nearby ambient temperature, reducing a building’s energy needs. In cold weather, the minimum daily temperatures on the green roof were higher than on the conventional roof.

The 15 native plants on the roof attracted birds and insects, including Australian stingless bees, spotted pigeons and evidence of a peregrine falcon.

Irga also spotted an Australian blue band bee, a solitary and beautiful bee that is rarely seen. “It blew everyone away,” he said.

The City of Sydney aims to increase green cover to 40 per cent by 2050, including 27 per cent canopy cover. There are 155,000 square feet of green roofs and walls like the Surry Hills Library.

Many countries have introduced incentives or laws to encourage green roofs and walls to offset the effects of climate change, reduce heat islands from hard surfaces, and make city life happier and quieter.

Toronto was the first city in North America to pass a green roof law. It required new buildings or additions larger than 1950 square feet to cover between 20 and 60 percent of their buildings with vegetation, she reported The New York Times.

As of 2011, there were 250 green roofs in Toronto, Irga said. More than 1000 were built or were under consideration.

The award-winning Bunkeren house near Newcastle has a cascading green roof. Architect James Stockwell describes it as landscape rather than terrace.

The award-winning Bunkeren house near Newcastle has a cascading green roof. Architect James Stockwell describes it as landscape rather than terrace.Credit: Tony Marshall

In Portland, Oregon, for example, zoning changes that required eco-roofs on every large building in the city’s commercial parks worked wonders.

This year’s NSW architecture shortlist also includes the new wing of the Art Gallery of NSW by Japanese architects SANAA with local Studio Architectus. It was nominated for the public architecture award.

John Jeffrey, senior associate at Architectus, said the green roof over habitable spaces contributed to a 35 percent improvement in the building’s insulation, reduced the load on the air conditioning system and contributed to the building’s six-star design rating.

It mitigates the heat island effect, absorbs rainwater and increases biodiversity by attracting pollinators. Rainwater is collected on site and used to water the plants, Jeffrey said more than 3740m2 of green roof – more than a full-size rugby pitch – has been planted with Australian wildflowers, including 3500 native yams.

Sydney's Modern Art Gallery.

Sydney’s Modern Art Gallery.Credit: Walter Peeters

Professor Sebastian Pfautsch, a specialist in urban heat at Western Sydney University, wonders why all new government buildings like the Art Gallery don’t have green roofs, which is mandatory in some parts of the world.

“It’s such a positive thing,” he said. “And where are the incentive programs to jump-start homeowners and businesses?” He said the changes in Portland have worked wonders, making green roofs more affordable. “An entire industry had taken root and it just became normal and cheaper to have green roofs installed.”

In Clareville, Martin worked with landscape architects Sprout Studio and gardeners Reflective Gardens to design the gardens, flower boxes and green roof.

The approx. 25 cm deep roof with earth and geotextile plastics for irrigation served many purposes. “They’re beautiful, they provide good thermal insulation and with the boxy style of modernist architecture, it’s a good opportunity to do more with a roof. They also bring a sense of calm and a slight purity to the air,” he said.

The author is a lay judge for the New Homes category in this year’s NSW chapter of the Australian Institute of Architects Awards. Winners will be announced in June.

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Jaclyn Diaz

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