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Roof Cleaning · Decision Guides

Roof cleaning decision guides

Clean if you have moss, which holds water against shingles and can lift their edges. Cleaning for black streaking alone is a cosmetic decision — ARMA identifies it as algae producing a pigmented sheath, not structural damage. If the roof is close to replacement anyway, cleaning it is usually money better saved.

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Work it in three questions. What is growing? Moss is worth removing. Algae streaking is cosmetic and mainly worth removing if appearance matters to you — before a sale, for example. Lichen sits between the two and is the hardest to remove cleanly.

How old is the roof? Get an honest read on remaining life first. If a roofer tells you three to five years left, a $255-$1,190 clean (Today's Homeowner's typical range) buys you appearance for a fraction of that. Weigh it accordingly.

Will it come back? Yes. ARMA states results are only temporary and discoloration will likely recur. So the honest question is not "will this fix it" but "is it worth this every two to three years?" Today's Homeowner's guidance is every 2-3 years for most homes and annually in humid or tree-covered locations. Multiply the cost by that frequency before deciding.

One decision that is not close: if you do clean, buy soft washing. ARMA's position is that a pressure washer should never be used on an asphalt shingle roof, so saving money by choosing high pressure means accepting granule loss and likely premature roof failure. Choose to clean or not to clean; do not choose to clean badly.

How to choose

Identify the growth before you buy a service
Moss, algae, and lichen are different problems with different urgency. Photograph the roof and ask the contractor to name what they see.
Get remaining roof life from a roofer, not a cleaner
A cleaning company has no incentive to tell you the roof needs replacing. That question belongs to someone not quoting you for a wash.
Multiply the cost by the frequency
At $255-$1,190 every 2-3 years, cleaning is a recurring expense. Compare that against branch trimming or algae-resistant shingles at your next re-roof.
Treat curb appeal as a legitimate reason
Cleaning for a sale or because the streaks bother you is a perfectly good reason. Just know you are buying appearance, not roof protection.
Never trade method for price
The cheap quote is usually cheap because of the method. On asphalt shingles that trade is not worth making.
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Roof Cleaning decision guides — common questions

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For moss, generally yes — it holds moisture against the shingle and can lift edges. For black algae streaking, it is cosmetic. ARMA describes the common cause as gloeocapsa magma producing a dark pigmented sheath, which is a staining problem rather than a structural one.
Removing moss plausibly avoids moisture-related damage. Removing algae staining mainly changes appearance. And done with the wrong method it does the opposite — ARMA warns pressure washing causes granule loss and very likely premature failure of the roof system.
Get a roofer's assessment of remaining life. If the roof has years left and the issue is growth, clean it. If it is near end of life, the cleaning cost is better put toward replacement, and you can specify algae-resistant shingles at that point.
Require soft washing in writing, verify liability and workers' compensation insurance directly from the insurer, ask what fall protection they use, and get landscape protection in the scope. Compare against Today's Homeowner's $255-$1,190 typical range — a quote far below it is a warning.
Sources

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