Soft washing is safe for asphalt shingles. Pressure washing is not. The Asphalt Roofing Manufacturers Association (ARMA) specifically recommends low-pressure washing combined with a cleaning solution as the correct method for removing algae and biological staining from asphalt shingles. High-pressure washing removes the protective granule layer from shingles, accelerating UV degradation and shortening roof life significantly.
Why granules matter
Asphalt shingles are composed of an asphalt-saturated felt or fiberglass mat coated with asphalt and embedded with ceramic granules on the exposed surface. Those granules do three things: they protect the asphalt binder from UV degradation, they add impact resistance, and they create the visible color and texture of the shingle. Once granules are removed, the underlying asphalt binder is directly exposed to UV radiation and begins to dry out, crack, and fail. Granule loss shortens the remaining service life of the shingle substantially.
A pressure washer running at 2,000 to 4,000 PSI directed at a shingle surface removes granules on contact. This is not a theory. Shingle granules are embedded, not chemically bonded, and high-pressure water dislodges them. You can observe this in the gutter discharge during and after an improperly done pressure wash.
What ARMA actually says
ARMA is the industry association representing asphalt shingle manufacturers. Their guidance on algae staining is clear: they recommend against pressure washing and specifically endorse a low-pressure solution of laundry-strength liquid chlorine bleach and water as a recommended cleaning method. Soft washing with sodium hypochlorite and surfactant aligns with this recommendation. Any contractor who uses a pressure wand on asphalt shingles is working against the manufacturer's guidance.
What soft washing does at 100 to 300 PSI
At 100 to 300 PSI, which is roughly the pressure of a standard garden hose, water does not dislodge granules. The cleaning work at this pressure level is done entirely by the chemistry, specifically the sodium hypochlorite oxidizing the Gloeocapsa magma bacteria and the surfactant keeping the solution in contact with the shingle surface long enough to kill the organism. The low-pressure rinse then removes dead material without mechanical stress on the shingle surface.
Will roof washing void my shingle warranty?
Using high-pressure washing on shingles may void warranty coverage on some manufacturer warranties, particularly if the damage to the roof is traceable to granule loss. Using soft washing in accordance with ARMA recommendations does not void manufacturer warranties. If your shingles are still within warranty and you are planning a roof cleaning, confirm the method with your contractor and retain the documentation.
How to identify an unsafe roof cleaning company
Before booking any roof cleaning, ask these questions:
- What PSI do you use on shingles?
- Do you use a dedicated soft wash pump or a standard pressure washer?
- Do you use a nozzle wand directly on the shingle surface?
Any answer that involves a pressure wand on shingles or PSI above 500 for roof surfaces is a red flag. Professional roof cleaning at the ARMA-recommended standard uses 100 to 300 PSI from a dedicated soft wash system.
CARE's safe roof washing in Fort Worth
CARE uses a dedicated soft wash system for all asphalt shingle roofs, operating at 100 to 300 PSI. No pressure wands are directed at shingle surfaces. Owner Stephen McPherson is on-site at every job. Call (945) 275-8031 or visit our roof cleaning page to schedule your roof cleaning.