Professional Roof Cleaning
in Seattle & the Eastside
Black streaks, green moss, and lichen take hold fast on Pacific Northwest roofs. We soft wash — never pressure wash — to remove growth safely and protect your roof's lifespan, following the method the roofing industry itself recommends.
Why Seattle Roofs Grow Moss, Algae & Black Streaks
Few climates are harder on a roof than the Pacific Northwest. Persistent rain, mild temperatures, heavy tree canopy, and long shaded stretches create near-perfect conditions for biological growth — and your roof is ground zero.
The dark streaks you see, especially on north-facing and shaded slopes, are a blue-green algae called Gloeocapsa magma. It feeds on the limestone filler in modern asphalt shingles, and the black color is a UV-protective sheath it builds. It spreads by airborne spores — which is why it tends to appear across whole neighborhoods. Moss is the bigger threat: unlike algae, moss has mass, holds moisture against the shingles, and can lift and curl shingle edges, raising the risk of water intrusion.
This isn't just about looks. Trapped moisture and granule loss shorten a roof's life — potentially by years — turning a routine cleaning into a premature replacement. Set against the cost of a new roof, regular professional cleaning is one of the clearest-value maintenance investments a homeowner can make.
How We Clean Roofs Safely — Soft Wash Only
The roofing industry is blunt about this: never pressure wash a shingle roof. Our method follows manufacturer-recommended practice from the first step.
Roof Inspection & Assessment
We assess your roof material, pitch, and condition — identifying algae streaking, moss buildup, and problem areas in valleys, ridges, and north-facing sections. A fragile or failing roof gets flagged before any cleaning begins.
Landscaping Protection
We pre-soak and protect all surrounding vegetation and landscaping so cleaning solution never contacts your plants — then rinse those areas again afterward.
Low-Pressure Soft Wash Application
We apply the appropriate biodegradable cleaning solution at low pressure and let it dwell, killing moss, algae, and lichen at the cellular level. No high-pressure blasting means no granule loss and no lifted shingles.
Gentle Rinse & Report
We rinse at low pressure; dead growth continues to weather off over the following weeks. You get a post-treatment walkthrough and condition report — including prevention advice tailored to your roof.
Roof Types We Clean
Different roofing materials demand different handling — but every one of them should be soft washed, never pressure washed:
Asphalt Architectural Shingles
The most common roof in Seattle. Soft washing removes gloeocapsa streaks and moss without stripping the protective granules that pressure washing destroys.
Cedar Shake & Shingle
Cedar is especially vulnerable to moisture and forced water. Our low-pressure method cleans without driving water under the shakes or raising the grain.
Tile (Clay & Concrete)
Tile can crack under pressure. We treat clay and concrete tile safely, preserving both the tile and its finish.
Metal Roofing
We remove oxidation, streaking, and biological growth from metal roofs while protecting coatings and seams.
Low-Slope & Flat
Commercial and low-slope roofs cleaned of the growth and debris that accelerate membrane deterioration.
North-Facing & Heavy Moss
Shaded, tree-covered, and north-facing sections grow the most. These get extra pre-treatment and, for heavy moss, sometimes more than one pass.
Roof Problems We Solve
Black Streaks (Gloeocapsa)
The algae streaking that runs down shaded slopes — killed at the source so it clears fully and stays gone 2–4 years, not weeks.
Moss Buildup
The high-mass growth that holds moisture and lifts shingle edges. Treated carefully, with repeat treatment for severe cases.
Lichen
Crusty, tightly-anchored lichen that's hardest to remove — dissolved at the root rather than scraped or blasted.
Granule & Lifespan Protection
By soft washing instead of pressure washing, we clean without the granule loss that shortens roof life by years.
Gutter & Debris Clearing
Roof debris and clogged gutters cleared so runoff drains cleanly and doesn't back up under the eaves.
Slower Regrowth
Because we kill growth at the root rather than just removing the surface layer, results last far longer — and we advise on the prevention steps that keep your roof cleaner between treatments.
We've used Homefront for three years running. They know our property, understand what we need, and always deliver without being asked twice. Worth every penny on Mercer Island.— Robert & Linda H., Mercer Island, WA · Annual House Wash & Roof Treatment
What Does Roof Cleaning Cost in Seattle?
Roof cleaning cost depends on your roof's size, pitch, material, and how much moss or algae has built up. We provide transparent, itemized quotes — and set against the cost of a premature roof replacement, regular soft washing is one of the most cost-effective maintenance investments you can make.
Roof Size & Pitch
Larger and steeper roofs take more time, material, and safety setup. We assess and quote accurately before work begins.
Moss vs. Algae Severity
Light algae streaking is a straightforward treatment; heavy, established moss may need pre-treatment and more than one pass, accounted for upfront.
Add-On Services
Gutter clearing and other add-ons can be bundled with your roof cleaning to protect the whole roof system in one visit.
The fastest way to an accurate price is a free quote. We respond within 24 hours — often same day.
Frequently Asked Questions
Why should a roof never be pressure washed?
The Asphalt Roofing Manufacturers Association (ARMA) — the industry authority — specifically warns against pressure washing asphalt shingles. High pressure strips the protective ceramic granules off the shingle surface, and those granules are the roof's main defense against UV damage. Once they're gone, they don't grow back, and the roof can fail years early. That's why the only correct method is a low-pressure soft wash: the cleaning solution kills the growth, and the roof is never blasted.
What are the black streaks on my roof?
Those dark streaks — usually worst on north-facing and shaded slopes — are a blue-green algae called Gloeocapsa magma. It feeds on the limestone filler in modern asphalt shingles, and the black color is a UV-protective sheath the organism produces. It spreads by airborne spores, which is why you often see it across a whole neighborhood. Left alone, it traps moisture and heat against the shingles and accelerates deterioration.
What's the difference between roof algae and roof moss?
Algae (the black streaking) is mostly a cosmetic and reflectivity problem — but moss is more serious. Moss has real mass: it holds moisture against the shingles, anchors into the surface, and can lift and curl shingle edges, raising the risk of water intrusion and blow-off. Both are treated by soft washing, but heavy moss may need more than one treatment and careful handling.
How long does a professional roof cleaning last?
Because soft washing kills the algae and moss at the source rather than just knocking off the surface layer, results on asphalt shingles typically last 2–4 years. Homes with heavy tree coverage, deep shade, or north-facing exposure may see growth return sooner — keeping trees trimmed back and gutters clear helps extend the interval between treatments.
Will roof cleaning void my shingle warranty?
Improper cleaning can. Pressure washing causes granule loss and can void manufacturer warranties, which is exactly why we never do it. Soft washing — low-pressure application of the appropriate cleaning solution — follows manufacturer-recommended practice. We treat your roof the way the roofing industry itself says it should be treated.
Have a question we didn't answer? Call (425) 298-7041 or submit a quote request — we respond within 24 hours.
Ready to Clean Your Roof? Book the Right Service
Roof cleaning is delivered through our dedicated roof service — and pairs naturally with the surfaces roof runoff affects:
Protect Your Roof Before It's Too Late
Black streaks and moss only get worse — and harder on your roof — the longer they sit. Get a free, no-obligation roof cleaning quote for your Seattle or Eastside home, usually same day. We serve Bellevue, Kirkland, Redmond, Sammamish, Bothell, Mercer Island, and surrounding communities.
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