Roofs that reflect the sun's radiation to prevent heat gain provide net energy and monetary savings even in colder climates, a new study published by researchers from Concordia University asserts.

“Using a cool roof on a commercial building in cold climates is typically not suggested based on the presumption that the heating penalties may be higher than the cooling savings,” says Hashem Akbari, professor in the Department of Building, Civil and Environmental Engineering and the study’s senior author. “Our research shows that any improvement to a roof that limits the summertime solar heat gain actually results in energy-cost savings for the building owner, as well as a reduction in the building's overall environmental impact.”

Cool roofs for commercial buildings can save energy in any climate that uses air conditioning in the summer. Image credit: Pixabay. For the study, Akbari and his co-author, PhD candidate Mirata Hosseini, used modeling software to simulate energy consumption for several prototype office and retail buildings in four cold-climate cities in North America: Anchorage, Milwaukee, Montreal and Toronto. They found that cool roofs for the simulated buildings resulted in annual energy expenditure savings in all municipalities.

A cool roof on a new medium-sized office building would save $4 per 100 square meters in Montreal, $10 per 100 square meters in Toronto and $14 per 100 square meters in Milwaukee and Anchorage. The research also showed that cool roofs can reduce the peak electric demand of the retail buildings by up to five watts per square meter.

“Our study proves that cool roofs for commercial buildings are a net saver of energy in all climates that use air conditioning during the summer,” says Akbari.

In cooler climates, installing cool roofs may even make buying an air conditioner unnecessary, the researchers report. "Even in non-air-conditioned buildings, cool roofs improve comfort during hot summer days," Akbari adds.

Many municipalities already prescribe cool roofs in the construction of new buildings and for re-roofing existing buildings. This study suggests that those rules should also apply in colder climates.

“On a large scale, cool roofs can moderate the air temperature surrounding a building, decrease greenhouse gas emissions and mitigate the urban heat island effect,” Akbari says.