How a “cool roof” could save you money

In classic Westerns, the good guy stays cool beneath his white Stetson. The black-brimmed villain twitches and sweats. Why so different? Light colours reflect solar radiation.

The science holds not only in Shane, but with hard hats, cars, and roofs, where the surface of a reflective “cool roof” is up to 33°C cooler than conventional asphalt roofing. Cool roofs “conduct less heat into the building,” says Hashem Akbari, a Concordia University professor of building, civil, and environmental engineering. “If your building is air conditioned, the load on the AC will be lower.”

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This makes white roll-on treatments and membranes, light-coloured metal, or reflective asphalt shingles an obvious choice in places where you’d run a wagon train. Farther north, cool roofs do marginally increase winter heating costs, but Akbari says this so-called “winter heating penalty” is typically outweighed by summer energy savings. “My general rule of thumb is a cool roof, on net, will save you money in any building where you need air conditioning in the summer and heating in the winter.”

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So why aren’t cottages, bunkies, and boathouses—especially seasonal ones with full sun exposure—sporting white lids? Fashion is a factor. Canadian roofs are usually black, grey, and brown, but that could change. Some companies sell dark-looking shingles with a coating that reflects 30 per cent of the heat absorbed by traditional shingles. And researchers are developing “dynamic cool roofs” that reflect solar heat in the summer and suck it up in the winter.

So next time you re-roof, consider whether your cottage might look ruggedly handsome beneath the structural counterpart of a white, pale grey, or tan Stetson. One thing is likely, says Akbari: compared to adding AC, choosing a reflective, cooling colour on the roof won’t cost a fistful of dollars.

This article was originally published in the June/July 2023 issue of Cottage Life.