Are cool roofs the future for Australian cities?

Are cool roofs the future for Australian cities?

Source: | 15 June 2022

A UNSW Sydney research team’s technological and cost-benefit analyses of adopting cool roof technology across major Australian cities has found that city-wide implementation of cool roofs would reduce energy bills, lower indoor temperatures, decrease urban heating and improve the health of vulnerable populations.

Cool roofs reflect more solar radiation than they absorb and, as a result, they stay cool in sunlight.

These cost-benefit analyses of cool roof implementation come a month after the new NSW Planning Minister, Anthony Roberts, scrapped a previous policy commitment to phase out dark roofs – a policy which would have reduced urban heating and energy costs for new homes.

The analyses undertaken by the High Performance Architecture team at the School of Built Environment at UNSW Arts, Design & Architecture was part of a project funded by the federal Department of Industry, Science, Energy and Resources (DISER) aimed at understanding the applicability and cost-benefit of using cool roof technology on buildings in Australia and any barriers to adoption.

“The study investigated the climatic, social, economic and environmental impacts of implementing cool roofs around Australia,” says Scientia Professor Mattheos (Mat) Santamouris, Anita Lawrence Chair in High Performance Architecture at UNSW School of Built Environment.

“We used simulated climatic modelling to understand conditions with and without cool roofs. The results showed urban areas, including Western Sydney, Perth, Melbourne, Adelaide, Darwin and Brisbane, had the most to gain from cool roofs.

“The need for cool roofs and other heat mitigation technologies should really be a priority,” says Professor Santamouris. “If not, the cost of climatic change in the next 10 to 15 years will be tremendous.”

Cool roofs reflect more solar radiation than they absorb, keeping surface temperatures lower as a result. Image: UNSW.

Cool roof technology provides savings on energy costs

The analyses looked at 17 types of buildings, ranging from low to high rise, commercial to residential and stand-alone to apartment blocks. Existing buildings with low insulation levels have the most to gain in energy savings by implementing cool roofs. Meanwhile, newer buildings with higher levels of insulation have relatively less scope for energy savings compared to less insulated buildings – but there are savings nonetheless.

The research found that cool roof technology will significantly reduce cooling energy consumption. Indoor temperatures in residential houses would be reduced by up to 4 degrees Celsius with a cool roof, with the number of hours exceeding 26 degrees Celsius reduced by 100 hours per summer compared to conventional roofs, which absorb sunlight rather than reflect it.

If the whole of Sydney implemented cool roofs, energy consumption for cooling residential and commercial buildings would decrease by up to 40 per cent in total.

“During summer, a building in Western Sydney will require double the energy to cool down compared to the same building in eastern Sydney,” says Professor Santamouris.

“Western Sydney is especially at risk of urban overheating, meaning the low-income households are more likely to either spend more on cooling or are forced to endure heat-related stress indoors. It’s a very serious problem.”

Temperature comparison between a dark regular roof and a white cool roof. Photos and data taken in Campbeltown area (NSW) in February 2018 in the late afternoon. Image: Supplied.

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