If you live west of the Cascades, moss on the roof is almost a rite of passage. Here's whether it's actually a problem, how to get rid of it without wrecking your shingles, and how to keep it gone.
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A little green fuzz looks harmless — but left alone, moss genuinely shortens a roof's life out here.
Constant moisture, shade from tall evergreens, and cool temperatures are exactly what moss needs. North-facing and tree-shaded slopes stay damp long enough for it to take hold and spread.
Yes, over time. Moss lifts the edges of shingles as it grows underneath them, holds water against the roof surface, and keeps the roof damp — which accelerates wear and can lead to leaks and decking rot. Thick moss also clogs gutters. It's cosmetic at first and a real problem if ignored.
If moss has been growing for years, shingles are lifted and brittle, and you're seeing granule loss or leaks, cleaning may only buy a little time. A roof inspection will tell you whether it's maintenance or replacement.
The growth you can see from the ground is the top of a mat that is already holding water in the keyway, between the courses, against the mat.
That is why pressure washing a moss-covered roof usually ends the roof rather than the moss.
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