How do you remove moss from a steel roof?—Chris Gunther, via email
Wait, moss grows on steel? Yes. Because moss grows wherever it damn well wants. All it needs is moisture and a little food. “Even though there’s no nutrition in steel, there is in the debris that falls on it,” says Gregg McBurnie, a former trained roofer and the owner of ROTban Ultra Cleaning in Coquitlam, B.C. Combine that with rain and shade, and moss can make a home for itself.
This is usually a cosmetic issue; moss isn’t likely to cause damage to a metal roof, says McBurnie. Still, you probably don’t want the stuff to sprout out of control. “Moss can grow in places where it then affects how rainwater drains off the roof,” he says. Ultimately, you could end up with a leak.
In no universe are we going to recommend that you get on your roof to tackle this problem. But if the moss is accessible—while carefully standing on a ladder, say—Philippe Laplante of Ideal Roofing in Ottawa suggests that you first try a garden hose with a sprayer.
“If a hose alone isn’t enough, try soap. Mix a quarter cup of soap per one gallon of water,” he says. Choose a biodegradable product if you want to be kind to the environment (which you do). “Apply the solution using a washcloth, a sponge, or a soft-bristled brush. The goal is to use the lightest touch that will do the job.” Let the solution sit for at least five minutes before rinsing it off.
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Will a light touch be enough to clean the roof to your satisfaction? That probably depends on how much moss you have and how much it bothers you.
You do have other options. You could hire a professional roof cleaner, or buy a commercial product and, for example, apply it with a backpack sprayer. But these options are likely going to be more expensive and less eco-friendly.
Plus, you could put your roof at risk. When it comes to metal panel maintenance, you’re always best to follow directions from the manufacturer, says Troy Ferreira, the technical director for the Canadian Roofing Contractors Association. “They may require specific cleaning methods, ones that won’t affect the metal or void any warranties.”
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Regardless of what you do to get the roof clean, to keep future moss at bay, “the biggest simple thing that you can do is give the roof good access to sunlight,” says McBurnie. You can’t stop the rain, but you can at least trim back branches that are shading the roof.
Got a question for Cottage Q&A? Send it to answers@cottagelife.com.
This article was originally published in the March/April 2025 issue of Cottage Life.
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