Get the moss off without wrecking the roof
Moss is the signature roof problem of western Washington. Shaded north-facing slopes, overhanging fir and maple canopy, and months of damp weather mean most roofs here grow it eventually, some by year five in the wooded towns.
Why it matters
Moss isn't just cosmetic. It holds water against the shingle surface, lifts edges as it thickens, and works into laps where freeze and rain finish the job. The black streaks on lighter roofs are algae; mostly a looks problem, but it often shows up alongside moss on the same damp exposures.
What cleaning should look like
- Loose growth removed first, brushed or blown off, not blasted
- Moss treatment, a product that kills the root layer over weeks, not a scrape that takes granules with it
- Gutter and valley clearing, the debris that feeds the growth usually sits there first
- Zinc or copper strips at the ridge where warranted, a slow-release deterrent on the worst exposures
What to avoid
High-pressure washing is the shortcut that costs you a roof. Pressure strips the protective granules off composition shingles and can split cedar outright. Any quote that leans on a pressure washer for a shingle roof deserves a second opinion. Hand removal plus treatment is slower and cheaper in the long run.
What should a quote include?
The method in writing, what's treated versus removed, gutter scope, whether preventive strips or treatment follow-ups are included, and a straight answer on whether cleaning is even worth it. A badly moss-eaten twenty-year roof may be at replacement age instead.
