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Sweltering through the summer? Researchers say reflective paint on roofs cools homes

It’s winter there now, but summers in Brisbane, Australia, are warm, with the hottest months in December through February. The country only recently came out of a decade-long drought, so it makes sense why researchers there are focused on way to reduce energy costs. One team of researchers is working on a material that keeps roofs cooler, while another has just completed a study that found a special coating helps reduce inside temperatures without air conditioning.

Related: Australian researchers’ polymer material keeps roofs cooler

Queensland University of Technology professor John Bell and senior research fellow Dr. Wendy Miller conducted a two-year study of homes, schools, offices, and other buildings in Brisbane and Townsville, Australia with roofs painted with the reflective coating. The paint job helped reduce rooms’ temperatures by 2 degrees Celsius.

Professor John Bell and Dr Wendy Miller

Professor John Bell and Dr Wendy Miller

The white paint keeps the roof cooler by reflecting 88 percent of the sun’s energy, compared to the 65 percent from a nonreflective, light-colored roof, and 25 percent of a dark-colored roof. A cooler roof means cooler classrooms, which makes students more comfortable and electricity bills lower. “We saw average energy savings of between 5 and 30 percent across the range of buildings, with most buildings showing savings above 15 percent,” Professor Bell said.

The researchers looked at 16 buildings in 10 locations, measuring temperatures before and after they applied the reflective paint. In one building, the temperature seldom crept above about 81 degrees Fahrenheit (27 degrees Celsius), which Bell says is cool enough that ceiling fans could replace air conditioners. “Twenty years ago it was cheaper and easier to put in an air conditioner than to paint your roof, but not anymore,” he says. The coating is a passive solution that takes less maintenance than central air, according to Bell.

Related: Cool it now: How to make your own DIY air conditioner

If you travel to the Cyclades islands, you’ll find most of the buildings are already painted white, because it reflects the sun best. The reflective paint likely wouldn’t have as dramatic of an effect there as it would on buildings with dark roofs. “The trials indicate the economic benefits of cool roof coatings would be greatest for single storey buildings; buildings with aged, dark-, or medium-colored roofs; buildings with no or low levels of roof insulation; and buildings with high air conditioning use,” Dr. Miller says.