Removing moss and algae from an asphalt roof

Old 02-23-18, 06:42 AM
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Removing moss and algae from an asphalt roof

I've got 3 moss / algae problems with my asphalt roof I want to address. The most annoying are the little chunks of moss that eventually detach and roll off the roof. Beyond that, I have a small section with green algae discoloration and a third section with a black algae streak beginning.

In terms of cleaning, what's the best option? I've read a lot about bleach but that may be too harsh and don't want to try it. Then there's sodium percarbonate that may be too mild. Power washing would probably work but the idea of climbing on the roof and making it slippery doesn't appeal to me either.

Thoughts, please.
Old 02-23-18, 07:00 AM
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Depending on the pitch, I would start by hosing it down with a siding wash solution, keep it wet with that a while, maybe gently brush it around with a stiff floor broom. But don't scrub hard on it. And yes, I think power washing is the key, but you always have to wash downhill, never drive water under the shingles or under flashings. And keep the wand a reasonable distance away.

As for the slickness, some shoes or boots are better than others so don't be afraid to try a few pair and use the ones that grip the best. Wearing fall protection is a given. Buy a few ridge d-rings, or hitch clips, get a harness and a 50' fall protection rope.

Power washing can remove grit and reduce the life of the shingles, but it's kind of a tradeoff if you want the roof clean. And the other thing is you might need to clean and wash it twice. The first time you do it it might leave uneven streaks.
Old 02-23-18, 10:57 AM
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Pressure washing will clean the roof nicely but as mentioned above it does shorten the life of the shingles. The few times I've pressure washed shingles it's been under protest at a realtor's request. Bleach should be ok providing you mix it with water and don't let it dry on the shingles.

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