Can you pressure wash a roof? Cleaning black streaks off asphalt shingles

Updated November 10, 2026 · KeystoneProGuide editorial team

Can an asphalt shingle roof be pressure washed?

No, according to the people who make the shingles. The Asphalt Roofing Manufacturers Association (ARMA) says not to use a power washer, or any type of brush or broom, to clean algae from a roof, and that high-pressure washing systems are likely to damage asphalt roofing. It says they should not be used to remove algae or for any other purpose, including other stains or dirt.

That is a trade association's guidance, but it comes from the makers of the product, and it is unusually direct. A company that proposes to pressure wash your shingles is proposing something the shingle makers say not to do.

What are the black streaks on my roof?

Often algae, which is easily taken for dirt or soot. ARMA says the discoloration is brown to black, may look uniform or form streaks, and is often mistaken for fungus, soot, dirt, moss or tree droppings. It names Gloeocapsa magma as probably the most prevalent of several species, says the algae are carried through the air, and says the pigment they produce can gradually turn a white or light-colored roof dark brown or black.

ARMA describes the problem as most widespread in the Gulf States and along the Northwest and Eastern Seaboards, while noting that it occurs to some degree everywhere, especially where conditions are warm and humid. Almost all kinds of roofing can be affected, it says, though the streaks show most on light colors.

Moss and tree droppings are different. ARMA says they usually leave only local patches, and for moss it says to consult the shingle manufacturer about its effects and how to remove it.

How do the shingle makers say to clean algae?

ARMA describes one method, with conditions:

1. Use a solution of liquid household bleach (sodium hypochlorite) and water. Mixing directions vary by shingle manufacturer and with the amount of staining, and ARMA says other chemicals or methods should not be used without the manufacturer's approval.
2. Disperse the solution gently on the roof, with eye protection and rubber gloves, and apply it carefully so it does not damage other parts of the building or the landscape around it.
3. Do not scrub. ARMA says friction may loosen and remove granules.
4. Work from a ladder or walkboards where possible, to avoid standing on the roof.
5. Leave the solution on for at least 15 minutes but no more than 20.
6. Rinse by gently spraying the roof with water.

ARMA is frank about the result. It says the effect is only temporary and the discoloration may recur.

Is it safe to do this yourself?

ARMA advises against it. It says the cleaning process makes a roof slippery and potentially hazardous to walk on, encourages the use of professionals to clean shingles, and recommends that only trained professionals walk, climb or work on a roof at all.

Bleach adds its own hazards. The U.S. Environmental Protection Agency (EPA) says never to mix chlorine bleach with cleaners that contain ammonia, because toxic fumes could be produced, and that gloves of natural rubber, neoprene, nitrile, polyurethane or PVC suit work with bleach. If the job involves a gas-powered pump or washer, the Consumer Product Safety Commission's warning about carbon monoxide from engines applies near open windows and doors.

What should you ask a roof cleaning company?

• "What will you put on the roof, and does my shingle maker approve it?" ARMA says products other than its bleach solution should not be used without the manufacturer's approval.
• "What pressure will you use?" The answer you want is a gentle rinse.
• "How will you protect the plants and the siding?" ARMA asks for care with both.
• "Is your product sold as a pesticide?" The EPA treats a product whose label claims to kill or remove a pest as likely to be a pesticide. Pennsylvania's Department of Agriculture requires a commercial applicator license to use pesticides on another person's property, and its page does not say how that applies to roof cleaners, so ask which license the company holds.
• "How long will the result last?" ARMA's answer is that cleaning is temporary.

What does roof cleaning cost?

Fixr says some materials, including asphalt roofing, can carry a premium of up to $2 a square foot. All of these are national figures. Some of the surveys describe their roof prices as pressure or power washing; whatever the label, ask what method the price is for. The cost guide has the wider ranges.

Is there a lasting fix?

Only at replacement time, by ARMA's account. It says several types of algae-resistant shingles are available, designed to inhibit algae growth for extended periods, and suggests considering them when you reroof if your roof appears vulnerable to algae.

Until then, ARMA's guidance amounts to a choice between living with the streaks and having them lightened, gently, from time to time. Soft washing vs pressure washing explains why the same low-pressure approach comes up for other surfaces too, and businesses offering the service are on the pressure washing directory page.

Sources

1. Algae Discoloration of Roofs, Asphalt Roofing Manufacturers Association (ARMA)
2. A Brief Guide to Mold, Moisture and Your Home, U.S. Environmental Protection Agency
3. What is a Pesticide?, U.S. Environmental Protection Agency
4. Pesticide Applicators, Registered Technicians, and Certification Exams, Pennsylvania Department of Agriculture
5. How Much Does It Cost to Pressure Wash a House? [2026 Data], Angi
6. How Much Does Pressure Washing Cost? [2025 Data], HomeAdvisor
7. Pressure Washing Prices, HomeGuide
8. How much does it cost to pressure wash the exterior of a house?, Fixr
9. Carbon Monoxide Fact Sheet, U.S. Consumer Product Safety Commission