Roof Cleaning
Soft washed, never pressure washed. Your shingle warranty stays intact.
The method
Asphalt shingles get a soft wash, not a pressure wash. A cleaning solution made for exterior use goes onto the roof first. It sits and works into the algae and moss. Then it's rinsed off at low pressure, well under a pressure washer's output. The solution does the cleaning. Water pressure only carries it on and rinses it off. That's why soft washing is its own method, not just a gentler pressure washer setting. It relies on dwell time and chemistry, not force.
Why it matters
Asphalt shingles are coated with mineral granules. Those granules shield the asphalt underneath from UV light and help protect against fire. High-pressure water can dislodge them, and once they're gone, they don't grow back. The same pressure can force water sideways, up under the shingle tabs and flashing. Roofs are designed to shed water down and off, not sideways. GAF and Owens Corning both list high-pressure cleaning among the practices that can void a workmanship warranty. The dark streaking itself is usually a colony of algae, often identified as Gloeocapsa magma. It feeds on the limestone filler in the granules, not soot or mildew. That's part of why a chemical treatment works on it and pressure alone doesn't.
What to expect
The crew applies the soft wash from the ground or the roofline edge, not by walking on the shingles. Walking the roof risks damage, especially when it's wet. The solution covers the full roof plane, including valleys and the areas around vents and flashing where debris and moisture collect. The dark streaking homeowners notice is a slow-growing algae, not surface dirt. It doesn't disappear the moment the solution is rinsed. The dead growth keeps lifting and washing away with rain over the following days. That's expected, not a sign the treatment didn't work.
Questions
Questions about roof cleaning
Why don't you pressure wash roofs?
High pressure can strip the protective granules on asphalt shingles. It can force water up under the shingle line instead of letting the roof shed it downward. It can also run against a shingle manufacturer's cleaning guidelines. Soft washing cleans the same algae and moss instead, using low pressure and a cleaning solution.
What causes the dark streaks on my roof?
Most dark streaking on asphalt shingles is a colony of algae, commonly Gloeocapsa magma. It feeds on the limestone filler in the shingle granules, not soot, mold, or dirt. That's why a plain rinse doesn't remove it, but a cleaning solution does.
Will the streaking come back?
Algae can return over time. Roofs stay exposed to the same moisture and shade that let it grow the first time. How quickly it comes back depends on the roof's sun exposure, tree cover, and pitch. Each of those affects how long the surface stays damp.
How soon will the roof look clean after treatment?
Not immediately. The solution kills the growth, but it doesn't lift off right away. The dead algae and moss wash off gradually, over the days after the visit, as rain rinses them away.
Get a quote for roof.
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