A company offers to pressure wash your mossy roof for cheap. It sounds efficient — blast the moss right off. Here's why roofing professionals, shingle manufacturers, and warranty documents all say the same thing: don't do it.
What Pressure Washing Does to Asphalt Shingles
Asphalt shingles are coated with ceramic granules that protect against UV rays and weather. A pressure washer operating at 1,500–3,000 PSI strips those granules right off — you'll find them piled in your gutters afterward. Without granules, shingles age rapidly, lose their fire rating, and develop leaks years early. The roof looks clean for a month. Then it deteriorates faster than before.
Worse: most shingle manufacturers explicitly exclude pressure-washing damage from warranty coverage. That "cheap" wash can void the warranty on a roof you paid thousands for.
What Soft Washing Does Instead
Soft washing uses garden-hose-level pressure combined with biodegradable cleaning solutions. The chemistry does the work — dissolving moss, algae, and lichen and killing them at the root — instead of water force tearing growth off the surface. Granules stay put. Warranties stay valid. And because roots are actually dead, regrowth is dramatically slower than after pressure washing, which leaves roots embedded and ready to resprout.
Side-by-Side Comparison
- Cleaning power: pressure washing wins on speed, soft washing wins on completeness (roots die).
- Shingle safety: pressure washing strips granules; soft washing preserves them.
- Warranty: pressure washing often voids it; soft washing is manufacturer-approved.
- Regrowth: faster after pressure washing (roots survive); slower after soft washing.
- Cost: pressure washing quotes are often cheaper — because the job is faster and less careful.
The One Exception
Concrete tile roofs can tolerate moderate pressure washing — tile is far harder than asphalt. Even then, soft washing is gentler and preferred. For asphalt shingles, cedar shake, and older roofs of any type, there is no exception: soft wash only.
Red Flags When Hiring
If a company's quote or website mentions pressure washing for asphalt shingles, walk away. Other warning signs: no mention of plant protection, no prevention treatment step, and pricing that seems too good — it's cheap because they're skipping the careful parts.
Quick Answers
Is it ever OK to pressure wash a roof?
On concrete tile or metal, controlled pressure can be fine. On asphalt shingles — never. High pressure strips the granules that protect shingles from UV, and most manufacturers list pressure washing as warranty-voiding.
How long does soft washing take?
Most Shoreline homes take 2–4 hours including setup, plant protection, treatment, and cleanup. Moss browns within days, with full clearing over a few weeks as dead growth weathers off.
Does soft washing use bleach?
Our solution is a diluted, biodegradable mix — strong enough to kill moss at the root, gentle on landscaping when we pre-wet, cover, and rinse properly. That's standard practice in the soft wash industry.
Get the Safe Clean, Not the Cheap Blast
Soft wash moss removal with prevention treatment included.
📞 Call (206) 555-0199