Ask House Spouse · PNW Seasonal · Spring Cleanup
How do I remove moss from my roof safely in the PNW?
Short answer
Don't pressure-wash a shingle roof — you'll shorten its life dramatically. Instead, apply a zinc-sulfate-based moss killer in dry weather, let it work for 1–3 weeks, then gently brush loose moss off with a soft roof broom or leaf blower. Install zinc strips along the ridge for long-term prevention.
Why not pressure-wash
Pressure washing strips the mineral granules from asphalt shingles — the granules that protect the asphalt from UV. Every square foot you pressure-wash cuts ~5 years off that shingle's life. On tile or metal roofs, pressure washing is safer but rarely necessary.
Chemical treatment done right
Apply moss killer during a dry stretch (48+ hours no rain after application). Most products contain zinc sulfate or copper compounds. Follow label directions for dilution and coverage; over-application can stain siding below.
Long-term prevention
Install a strip of galvanized zinc along the roof ridge — rainwater carries dissolved zinc down the roof and inhibits moss growth for 20+ years. This is a cheap add during any other roof work; $150–$400 total for most PNW single-family homes.
What we see on Home Health Assessments
Around 74% of PNW roofs we assess show active moss establishment — accelerates shingle wear by an estimated 3–5 years if untreated.
Caught early on assessment: $220–$650 · Left until failure: $3,500–$22,000
Based on real experience across Snohomish and King County, pnw seasonal issues like this are among the ones homeowners most often miss until they become expensive. Our Home Health Assessment catches them early — while they're still a maintenance item, not a repair.
How the Home Health Assessment worksServices we'd bring to this job
Related questions
Exterior & Weatherproofing · Gutters & Downspouts
How often should I clean gutters in the Pacific Northwest?
Twice a year minimum — once in late fall after the leaves drop (mid-November) and once in spring (late March). Homes surrounded by Douglas fir, cedar, or big-leaf maple need a third mid-fall cleaning, typically late October. Skipping cleanings is the #1 cause of preventable siding and foundation damage we see.
Exterior & Weatherproofing · Decks & Outdoor Structures
How often should a deck be stained or sealed in the PNW?
Semi-transparent stain lasts 2–3 years on a PNW deck; solid stain lasts 4–6 years; clear sealer lasts 12–18 months. Whichever you use, plan on a full clean and re-coat schedule and stick to it — a deck that's gone gray from neglect needs more than a re-coat, it needs board replacements first.