The short version
- Shingles are covered in mineral granules that shield the asphalt underneath from the sun.
- A pressure washer knocks those granules off. The roofing manufacturers' association says that causes granule loss and very likely premature failure of the roof.
- Roofs are cleaned with a solution, not force: applied at low pressure, given time to work and rinsed gently.
What's on top of a shingle
An asphalt shingle is a mat soaked and coated in asphalt, topped with a layer of small mineral granules. Those granules aren't just for color. Home inspectors' association InterNACHI explains that losing granules increases the amount of UV radiation reaching the asphalt, and UV deteriorates asphalt (InterNACHI). Consumer Reports adds that the granules help extend the shingles' lifespan (Consumer Reports).
Shingles lose a few granules naturally as they age. The problem is speeding that up all at once.
What a pressure washer does to it
A pressure washer is built to strip things off surfaces. On a roof, the thing it strips is the granule layer. The Asphalt Roofing Manufacturers Association (ARMA) is blunt:
- "Never use a pressure washer to clean an asphalt shingle roof as this will cause granule loss and very likely premature failure of the roof system" (ARMA).
- Don't use a power washer, or even a brush or broom, to clean algae from the roof surface, and high-pressure systems are likely to damage asphalt roofing (ARMA).
- Consumer Reports also warns that a high-pressure stream can loosen shingles (Consumer Reports).
Why the damage is permanent
Granules are embedded in the asphalt when the shingle is made, and there's no way to put them back. Once they're gone, that patch of shingle has less protection from sun and weather for the rest of its life. The roof may look cleaner for a while, but it's also older than it was the day before.
How roofs are cleaned instead
The black streaks on most roofs are algae, not dirt (ARMA), which is why chemistry works better than force. ARMA's own guidance describes the approach: apply a cleaning solution with a sprayer, let it dwell on the roof for 15 to 20 minutes, then rinse thoroughly with low-pressure water, and avoid letting the solution dry completely, because that may prevent complete rinsing (ARMA). ARMA also says the algae will wash away with later rains.
That's the method the trade calls a soft wash. We don't publish mixing recipes here, because ARMA says other chemicals or methods shouldn't be used without the shingle manufacturer's approval (ARMA). Follow your shingle maker's instructions. For more on the streaks themselves, see black streaks on your roof, and for why the waiting matters, what dwell time means.
Safety note: ARMA warns that cleaning makes a roof slippery and recommends that only trained professionals walk or work on roofs (ARMA). Consumer Reports advises never using a pressure washer from a ladder, because the kickback can knock you off balance (Consumer Reports).
What about tile or metal roofs?
This page is about asphalt shingle roofs. Tile, metal and other roofs have their own manufacturer care instructions, and those come first. ACE takes roof jobs, including tile and metal, when the roof can be cleaned safely. Ask us.
ACE and roof jobs
ACE takes roof jobs when the roof can be cleaned safely. Ask us. On shingles, that means a low-pressure soft wash, never high pressure. Our soft wash equipment is an X-Jet nozzle, which can reach up to 40-plus feet from the ground, according to its maker (X-Jet).
Quick answers
Can you pressure wash a shingle roof?
No. The Asphalt Roofing Manufacturers Association says never to use a pressure washer on an asphalt shingle roof, because it causes granule loss and very likely premature failure of the roof system.
What do the granules on shingles do?
They protect the asphalt underneath. InterNACHI explains that granule loss increases the amount of UV radiation reaching the asphalt, which deteriorates it, and Consumer Reports notes that the granules help extend the shingles' lifespan.
How should a shingle roof be cleaned?
With a cleaning solution applied at low pressure, left to dwell and then rinsed with low-pressure water. ARMA describes letting the solution dwell 15 to 20 minutes and avoiding letting it dry completely. Follow your shingle manufacturer's instructions.
Is it safe to clean my own roof?
Roof work is dangerous. ARMA warns that cleaning makes a roof slippery and recommends that only trained professionals walk or work on roofs.
Sources
- Algae Discoloration of Roofs, Asphalt Roofing Manufacturers Association (ARMA). https://www.asphaltroofing.org/algae-discoloration-of-roofs/
- Algae & Moss Prevention and Cleaning for Asphalt Roofing Systems, Asphalt Roofing Manufacturers Association (ARMA). https://www.asphaltroofing.org/algae-moss-prevention-cleaning-asphalt-roofing-systems/
- Mastering Roof Inspections: Asphalt Composition Shingles, Part 30, InterNACHI. https://www.nachi.org/asphalt-comp-shingles-part30-84.htm
- Can You Pressure-Wash It?, Consumer Reports. https://www.consumerreports.org/home-garden/pressure-washers/surfaces-safe-to-clean-with-a-pressure-washer-a5445180933/
- The X-Jet M5, X-Jet. https://xjetnozzle.com/the-x-jet-m5/
Links checked October 19, 2026. This page is general information, not a substitute for your manufacturer's instructions or a product label.