Moss on the roof is a fact of life here, and left alone it does real damage. But the way a lot of people clean it off does damage too. Here is how to handle it without wrecking the shingles.
Why moss is a roof problem, not just a look
Moss holds water against the shingles and creeps under them, which lifts the edges and keeps the surface wet. On a north-facing slope in the Pacific Northwest it comes back every year. Left long enough it hides soft decking underneath.
Skip the pressure washer
A pressure washer blasts the protective granules right off asphalt shingles and can force water under them. It looks clean for a season and takes years off the roof. It is the most common way people damage a roof while trying to help it.
The gentler way that works
Brush off the loose moss with a soft brush, working downward so you don't lift shingles, then treat the roof with a moss killer made for it. Zinc or copper strips near the ridge cut down regrowth over time. Slow and gentle beats fast and harsh here.
When the moss is telling you more
If the moss is thick and the roof is old, the growth may be sitting on decking that has already gone soft. That's worth a real look before you spend on cleaning a roof that is near the end anyway. We get up there and tell you which it is.
Common questions
Before you pay to clean shingles that are about done, have us check the decking under the moss first. If the roof is sound, we'll say so, and brushing and treating it is work you can do yourself.
