Can You Pressure Wash an Asphalt Shingle Roof?

No — not at any pressure, and not for stains, moss or grime. Each of the three shingle manufacturers whose cleaning guidance was read for this page tells its customers not to use one, and the association that writes the industry’s technical bulletins puts it more broadly still: high-pressure washing systems “are likely to damage asphalt roofing and should not be used to remove algae or for any other purpose.”

The reason is not the water but what it carries away. The granule layer pressed into the top of a shingle blocks sunlight from the asphalt underneath, and once it is stripped off it does not come back. What the makers publish instead is chemical — a bleach solution, a dwell time and a low-pressure rinse — at a strength set by the maker of the shingles on your roof, not by a general rule of thumb.

Three things decide it:

• The surface. No document read for this page permits a pressure washer on asphalt shingle; four name it as a thing not to do.
• The mechanism. Granules strip, and the asphalt they were shielding ages faster without them — the same loss the association ties to brush and broom friction.
• What is left. A bleach solution at the strength the shingle’s own maker publishes, and a low-pressure rinse — applied by someone trained to be on a roof, which this publication does not claim to be.

What the pressure actually removes

A shingle is a fiberglass mat, an asphalt coating and a layer of mineral granules pressed into it, and the granules are not decoration first. They “help protect shingles and their binder, the asphalt, from solar ultraviolet radiation,” Malarkey Roofing Products states in its technical bulletin on granule loss. CertainTeed describes the same function: granules “block ultraviolet (UV) light from reaching the asphalt,” and ultraviolet light reaching unprotected asphalt “will age the asphalt prematurely.”

That layer is what a pressure washer attacks. IKO describes the mechanism: a pressure washer can be “strong enough to break a shingle’s adhesive and lift it up,” and it “can strip asphalt shingles of their granule surface.” The association adds a second mechanism that has nothing to do with pressure: “Avoid scrubbing the surface, as this friction may loosen and remove granules.”

Some loss is normal, and worth knowing before the gutter is read as a verdict on the roof. Malarkey’s bulletin explains that surplus granules, called hitchhikers, work loose after installation, “typically end up in gutters,” and that losing them “does not affect the performance or lifecycle of the shingles.” More-than-normal loss follows severe weather — high winds, hail, ice dams, inadequate ventilation. None of that makes pressure washing harmless: the gutter is not a diagnosis, and the layer removed by force was doing the protecting.

What the makers say, in their own words

There is no published pressure setting that makes it safe

None of the documents read for this page gives a number at which washing a shingle roof becomes acceptable; the prohibitions are written without one. IKO rules out “any amount of pressure washing.” The association rules out the machine and the broom in a single sentence, and its scrubbing warning is about friction rather than force — which is what the “just keep it on low pressure” advice misses, because a setting on the wand is a detail of the machine, and the instruction is about the shingle.

Pressure figures published for other surfaces — fiber-cement cladding, concrete flatwork, brick, pavers — belong to those materials; none transfers to a shingle roof.

What the makers publish instead

The method they describe is chemical. The association gives a 50:50 mix of laundry-strength liquid chlorine bleach and water, applied with a sprayer, left 15 to 20 minutes and rinsed thoroughly with low-pressure water — with the instruction not to let it dry, because that may prevent a complete rinse, and to protect landscaping and surrounding areas.

The makers then differ, and the difference is the point:

• GAF prints its own mixture in the bulletin that forbids the pressure washer: 4 gallons of water, 1 gallon of bleach, 1 cup of trisodium phosphate or a phosphate-free substitute, sprayed on, left up to 20 minutes, rinsed at low pressure.
• Owens Corning publishes one gallon of bleach to one gallon of water, left 10 to 20 minutes, with ground vegetation covered and flushed afterwards.
• IKO gives a 50:50 bleach-and-water mix for algae staining, while its moss guidance prefers a bleach-free EPA-rated moss cleaner or a milder mix, and warns that high concentrations of bleach can do permanent damage.

Every one of these documents says to protect plants, and none presents the result as permanent: the association states that the cleaning’s effectiveness “is only temporary, and the discoloration may recur.”

One divergence is worth recording rather than smoothing over: Owens Corning’s cleaning guidance recommends a low-pressure soft wash and says to avoid using chemicals, while its algae guidance on the same website publishes a bleach mixture and a dwell time. The practical instruction is the same one the rest of these documents give: the method and the strength for your roof are set by the maker of the shingles on it, so the document to find is the one that names your product.

What the warranty clause actually says

The shorthand is that pressure washing voids the warranty; the documents are more specific. Owens Corning’s Standard Product Limited Lifetime Warranty — publication 10023873, printed August 2026 — lists among what it does not cover “damage to the shingles caused by alterations made after completion of application, including … power washing, painting, the application of cleaning solutions not in accordance with our algae removal instructions, coatings, or other modifications.” IKO says it in a sentence: “Using any of these methods may also void your limited warranty on the roof.” GAF’s warranty is drawn differently again, excluding damage “resulting from anything other than an inherent manufacturing defect” — the same exclusion in general form.

Algae staining is treated separately. Both documents read here exclude discoloration caused by algae, mold, fungus or lichen — except the blue-green algae coverage attached only to shingles sold under the makers’ algae-resistant labels, where the remedy can be the reasonable cost of cleaning them. Find out which product is on the roof, keep the paperwork, and note the 30-day window both set from discovering a problem.

What would end the question

Algae-resistant shingles do, at replacement rather than during a cleaning. They carry copper-bearing granules, and the association’s position is that these products are “specifically designed to inhibit algae growth for extended periods of time”; the makers attach algae warranty periods of 10, 25 or 30 years to their labelled lines. One caveat comes with the technology, from Owens Corning’s warranty: in some coastal areas and areas with limited rainfall, copper released by those granules can corrode aluminum gutters, which is why it recommends vinyl gutters there and states it will not be liable for that damage.

Everything else that reduces growth is off-roof work, and it belongs to the roof maintenance guide. Moss, the growth the association ties to lifted shingle edges and water driven sideways into the deck, is its own decision: roof moss in Washington.

Where this shows up in Washington, and where the water goes

The state sits inside the problem: the association’s bulletin states that algae discoloration “is most widespread in the Gulf States and along the Northwest and Eastern Seaboards.” Growth pressure differs between the damp west side and the dry east side, and that difference changes the maintenance calendar rather than the method — shade and debris do the work everywhere, and on the east side the debris carries a fire-season deadline, which the roof maintenance guide sets out.

A roof wash also produces runoff, which leaves through the gutters and downspouts. Where wash water may go, and what has to be protected or captured, is a regulated question with its own page here and applies to a roof as much as to a driveway: wash-water and runoff planning.

If you are hiring the work

The association’s warning closes the do-it-yourself route for most homes whatever the pitch: “Because it is dangerous to walk, climb, or work on a roof, ARMA recommends that only trained professionals engage in such activity,” and the treatment makes the surface slippery. This publication does not describe roof access or application work; everything above is the maker’s instruction to whoever performs it.

What you can do is make the method part of the conversation in writing: which method; what solution, at what strength and for how long; how the rinse and runoff will be handled; and whether the work will follow the instruction published by the maker of your shingles. A contractor whose answer for a shingle roof is a pressure washer for everything has answered the question for you. Checking a Washington contractor’s registration, bonding and insurance is a separate errand.

Next step

Work from the ground with binoculars and photograph what you see, with the date. Then find which shingle product is on the roof — the paperwork from the last reroof, or a bundle label kept in the garage, is what makes the maker’s instruction findable. The dark streaking is an appearance matter on standard shingles; moss is the growth the association ties to lifted edges, trapped moisture and eventually leaks. Neither is answered with a pressure washer, and the treatment the makers publish is the one to have quoted.