The safe PSI range for cleaning asphalt shingle roofs is 100 to 300 PSI, applied through a dedicated soft wash system, not a standard pressure washer wand. At this pressure, the cleaning is done by chemistry, specifically sodium hypochlorite and surfactant, rather than mechanical force. ARMA, the Asphalt Roofing Manufacturers Association, recommends against using high pressure on asphalt shingles because it removes the protective granule coating.
Why the PSI limit is so low for roofs
Asphalt shingles derive their UV protection from a layer of ceramic granules embedded in the surface. These granules are held by the adhesive properties of the asphalt binder, not by mechanical bonding. High-pressure water, anything above roughly 500 PSI on a shingle surface, dislodges granules through mechanical impact. The loss of granules exposes the underlying asphalt to UV radiation, which dries it out and accelerates cracking and brittleness.
At 100 to 300 PSI, roughly the pressure of a strong garden hose, water does not have the force to dislodge embedded granules. The soft wash solution applied before rinsing does all the actual cleaning work at this pressure range.
The difference between soft wash equipment and a pressure washer
A standard residential or commercial pressure washer is designed to deliver 1,500 to 4,000 PSI. Even at its lowest setting, most pressure washers deliver more force than is appropriate for roof shingles. Soft wash systems are different pieces of equipment. They use a lower-volume, lower-pressure pump designed to deliver solution at 100 to 300 PSI, with larger orifice nozzles that maintain volume flow at low pressure. You cannot approximate a soft wash system by turning down the pressure on a standard pressure washer, because the flow dynamics are different.
What happens when contractors use too much pressure on roofs
The damage from high-pressure roof washing is not always immediately catastrophic, which makes it hard for homeowners to catch. The visible signs appear over time:
- Granule accumulation in gutters: During or shortly after a high-pressure wash, granules wash off and collect in gutter troughs. This is the clearest immediate indicator.
- Color variation: Sections of the roof where pressure was concentrated look lighter because granules are gone and the lighter asphalt binder is exposed.
- Accelerated brittleness: In the months after a high-pressure wash, UV exposure degrades the now-unprotected asphalt faster. The shingles feel and look dry, and edge cracking begins earlier than it should.
These signs may not be obvious until the season after the cleaning, making it important to choose the right method upfront rather than discovering the damage later.
Does 100 to 300 PSI actually clean anything?
Yes, when combined with the appropriate chemistry. The sodium hypochlorite in the soft wash solution oxidizes and kills Gloeocapsa magma on contact. The surfactant keeps the solution against the shingle surface long enough for this reaction to occur. After adequate dwell time, a 100 to 300 PSI rinse is more than sufficient to remove the dead material from the shingle surface. The cleaning is accomplished by the chemistry. The water is the delivery and rinse vehicle.
What about other roofing materials?
The 100 to 300 PSI guidance applies specifically to asphalt shingles. Other materials have different guidelines:
- Concrete and clay tile: Can tolerate higher pressure, typically 800 to 1,200 PSI, but soft washing is still preferred for biological growth.
- Metal roofing: Soft wash chemistry is effective. Higher pressure is less risky than on shingles but rarely necessary.
- Wood shake: Requires low pressure, 500 PSI or below, to avoid raising the grain or splitting the wood.
CARE's roof cleaning PSI standard
CARE uses a dedicated soft wash system for all asphalt shingle roofs, operating at 100 to 300 PSI. No standard pressure wand is used on shingle surfaces. Call (945) 275-8031 or visit our roof cleaning page to schedule service.