Pressure Washing Roof Damage: What High Pressure Does to a Roof

The short version

Can pressure washing damage a roof?

Yes. The shingle makers' trade group says high-pressure washing is likely to damage asphalt roofing.

The Asphalt Roofing Manufacturers Association (ARMA) speaks for the companies that make asphalt shingles. Its technical bulletin on algae says not to use a power washer or any type of brush or broom to clean algae from a roof. It adds that high-pressure washing systems are likely to damage asphalt roofing and should not be used for algae or for any other purpose, including cleaning dirt or other stains.

Tile roofs have limits too. An Eagle Roofing care article that points readers to the Tile Roofing Institute Alliance says to use water only, with pressure never above 1,200 pounds per square inch (psi).

Here is a plain note about Coastline. We do not clean or pressure wash roofs, and we do not offer soft washing. We do inspect roofs with a written photo report, and we repair roofs. If a wash left your roof worse off, we can look at it. Our roof maintenance page lists what we do offer.

The gentle way

What does low-pressure cleaning look like for shingles?

It is a low-pressure rinse and a short soak, not a blast. Coastline does not do it, and ARMA says to use a professional.

ARMA's bulletin describes a low-pressure approach for shingles. ARMA says the mixing directions vary among shingle makers, and that other cleaners or methods need the shingle maker's approval. Read your shingle warranty paperwork before anyone touches the roof. In plain steps, the approach looks like this.

1. Check with the shingle maker

   Find out what your maker allows. ARMA says directions for the cleaning solution differ among makers.

2. Protect the surroundings

   The solution can damage plants and other parts of the building, so ARMA says to apply it carefully and wear eye protection and rubber gloves.

3. Apply gently, do not scrub

   The solution should be gently dispersed on the roof surface. ARMA says to avoid scrubbing, because the friction may loosen and remove granules.

4. Let it sit for 15 to 20 minutes

   ARMA says to leave the solution on at least 15 minutes and no more than 20.

5. Rinse with a light spray

   Rinse the solution off by gently spraying with water. ARMA warns the roof is slippery and hazardous to walk on during the process.

6. Expect it to come back

   ARMA says the effect is temporary, and the discoloration may return.

ARMA also says to work from a ladder or walkboards if possible, and that only trained professionals should climb on roofs. If you do hire someone, ask them to follow your shingle maker's instructions in writing.

If your roof is already near the end of its life, a washing may not be the best use of money. The signs you need a new roof page helps you decide, and our roof maintenance checklist covers upkeep that does not involve a power washer.

After a wash

What should I check if my roof was already pressure washed?

Look for bare spots, granules in the gutters, cracked tile and new leaks.

If a crew already used high pressure on your roof, do not panic. Do a simple check from the ground and from inside the house.

• Look for lighter or bare patches on shingle roofs. Check the ground and downspouts for loose granules. Our granules in gutters guide explains what that means.
• Look for cracked, chipped or slipped tile.
• Check ceilings and the attic for new stains or damp spots after the next rain. If you see one, see what to do about a roof leak.

Do not climb up to check. A written photo report from an inspection shows the roof up close without anyone walking on wet shingles or tile. Coastline does roof inspections with a written photo report, and can do the repair if something needs it. We do not clean roofs, but we are glad to tell you what we see.