We’ve talked before about our old friend Gloeocapsa magma—the black mold-like streaks and stains that can appear on roofs. In actuality, it’s a blue-green alga that is particularly attracted to light-colored asphalt shingles. This alga thrives in places that have warm, humid summers, so don’t be surprised if you find it on your roof.
It’s important to note that this alga doesn’t harm your roof at all. It’s more an aesthetic nuisance than anything else. That said, if you decide not to address it at all, it can prematurely age your roof. No damage done, but you still might need to replace it sooner than you would otherwise. Of course, if your roof is receiving regular maintenance, you already have someone keeping an eye on its overall health, so you could be fine just leaving it as-is.
Let’s assume you’ve noticed that you do, indeed, have black streaks on your roof and you want it gone. Good news! You have a few options.
The first is to replace your shingles, which may or may not make sense, depending on the age of your roof. A darker shade of shingle will more readily disguise the presence of gloeocapsa magma. If you want to do one better, you can select shingles that are laced with copper granules, which are lethal to algae.
But if your roof has a few years of life left in it, then replacing it on account of algae is not the most cost-effective solution. Your instinct might be to reach for the power washer, which—and we can’t emphasize this enough—is a really bad idea. A pressure washer can do serious damage to your shingles and, being that the damage would have been self-inflicted and not incurred during a storm, your insurance company definitely wouldn’t cover the cost for repairs.
However, a light spray (50% water and 50% bleach) can be effective in killing any gloeocapsa magma that already exists on your roof. If you go this route, we recommend wetting your foundation plantings ahead of time to give them a layer of protection while you’re applying the spray. Afterward, rinse everything with clean water.
The other option is, of course, to contact your friends at Dale’s Roofing. We’re happy to take a look and provide some ways to not only get rid of those black streaks but prevent them from returning.