If you’ve lived in Northwest Washington for a while, you’ve seen it: the north side of the roof turning green, then fuzzy, then thick with moss. Our long wet season, mild temperatures and tall shade trees make roofs here some of the best moss habitat in the country.
Moss isn’t just a looks problem. Here’s what it does, what not to do about it, and why fall is a smart time to treat it.
What moss does to a roof
Moss acts like a sponge. It holds water against the roof surface long after the rain stops, and the roof never really gets a chance to dry out. Over time that can:
- Lift and curl the edges of asphalt shingles as moss grows underneath them
- Hold moisture against the roof deck and fasteners
- Shed clumps and debris that clog gutters and downspouts
- Encourage lichen and algae, which spread alongside it
Roofs, siding and hard surfaces are constantly exposed to lichen, moss, algae, pollen and restricted airflow. Left untreated, all of these speed up wear — and a roof is the most expensive surface on the house to replace.
Why fall is a good time to treat moss
Moss is actively growing through our wet months. Treating it in the fall means it’s dealt with before it has a whole winter to spread and dig in. Dead moss also loosens over the following weeks and rain helps wash it away, so a fall treatment sets the roof up to look much better by spring.
It also pairs well with a fall gutter cleaning. Clearing the roof and gutters together means the debris that comes off the roof isn’t left sitting in your gutters all winter.
What not to do
Don’t blast it off with a pressure washer
High pressure can strip the protective granules off asphalt shingles and force water up under them. Roofing manufacturers and the Asphalt Roofing Manufacturers Association (ARMA) recommend low-pressure cleaning methods instead.
Don’t use powdered laundry detergent
It’s a common internet tip, but powdered laundry detergent is not an approved roof cleaning application, and it will void your roof’s warranty.
Don’t put off maintenance
Roofs are manufacturer-recommended to be washed annually, and deferred maintenance can void your warranty. A roof left mossy for years is harder to clean and more likely to have damage underneath.
How our moss treatment works
Our roof soft wash and moss treatment is ARMA-approved, so it preserves your roof warranty. We use 12v backpack sprayers to get 100% surface coverage, plus a second application in high-occurrence areas — usually the shaded sides and the spots under overhanging trees.
- ARMA-approved and warranty-safe
- Unlimited 12-month warranty against new moss from the time of service
- Safe for tile, composite and metal roofs — and we specialize in metal standing-seam
Get a free roof moss quote
We treat roofs across Skagit, Island, Whatcom and Snohomish Counties. Call or text (360) 800-3486, or request a quote online. Clear photos of your roof help us price it quickly; for bigger or more complicated roofs, we recommend an on-site quote.
