How to Remove Algae from Roof Shingles

How to Remove Algae from Roof Shingles

Moss covering asphalt shingles on a roof

Here in Oregon, mostly blue-green algae grows on the outside of the house or on the roof shingles. The only way to take care of it is to use a high-base chemical solution, like zinc sulfate. We’ll explain more of that in a bit.

While some people actually like the look of moss on their roof, they may be unaware that it can damage your roof, even promote rot.

What happens is the algae grows and becomes food for the moss. That moss then collects rainwater, like a sponge. If that top layer of moss gets heavy enough, the moisture seeps under the roof shingles and into the understructure. This brings mold build-up and eventually decay.

That means if you see algae or moss on your roof shingles, it’s time to remove it. Here’s how.

Cleaning your roof without damaging it

First we need to say one thing: don’t ever use a high pressure washer on your roof (for some reason it’s the first thing many people think to do). That pressure can strip granules and protective elements from shingles – it’s almost like wearing away the tread on a tire. Doing this means you’ll have to replace your shingles sooner.

Other people broom off the moss, which does work, but stiff bristles could also wear away the granules.

One of the most effective moss killers is zinc sulfate

Zinc sulfate most often comes in powder form. To start cleaning, apply it directly and generously to moss areas – it’s recommended to use three pounds of powder for every 600 square feet. Spread it along the ridge of the roof, then let the rain do it’s job of dissolving it.

Generally, this takes care of moss for 1-3 years. The zinc needs to be applied annually though to keep the algae from regrowing, similar to how chlorine gets added regularly to maintain the cool blue color of your pool.

Here’s the downside: zinc sulfate is damaging to plants if it hits them directly. That’s why, before using it, most people will drape their plants to protect them. We also recommend applying it on a calm day, so the wind doesn’t spread it further than where it needs to be.

Early removal is best for long-time protection

Taking care of algae growth early on is a very important way to ensure longevity for your roof. The more you let it grow, the higher the likelihood of seeing further damage.

Do you have questions, or need help cleaning your roof? Call the experts at Pacific West Roofing for any assistance.

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