How to Remove Moss from a Roof Safely (and Stop It Coming Back)

Reviewed by The Roofing Brief Team. Last reviewed: October 2026.

To remove moss from an asphalt shingle roof, spray a diluted bleach solution (or a cleaner your shingle maker approves) gently onto the moss, leave it for the time the maker specifies (15 to 20 minutes for bleach under ARMA guidance), rinse with low-pressure water aimed down the slope, and let rain and a leaf blower clear the dead moss over the following weeks. Do not pressure wash or scrub. The Asphalt Roofing Manufacturers Association (ARMA), GAF, Owens Corning and CertainTeed all advise against pressure washing shingles, and Owens Corning’s limited warranty excludes damage caused by power washing. Prevention comes from trimming shade trees, clearing debris and keeping gutters flowing. ARMA does not recommend adding zinc or copper strips to an existing shingle roof.

The Short Answer: 3-Step Removal + Prevention

1. Apply the treatment. Use your shingle maker’s bleach recipe or a moss product your shingle maker approves. Spray it gently with a pump sprayer from a ladder or walkboards. ARMA says other chemicals should not be used without the shingle manufacturer’s approval.
2. Let it work for the specified time. For bleach, that is 15 to 20 minutes under ARMA’s guidance (ARMA’s current bulletin says at least 15 and no more than 20 minutes). For a branded product, follow the label.
3. Rinse gently from above. Use a garden hose at low pressure, spraying down the slope. A GAF RoofViews article notes that spraying upward against the shingles can cause them to lift and possibly warp.
4. Prevent regrowth by trimming branches, clearing debris with a leaf blower aimed down the slope and keeping gutters clear, as ARMA recommends.

Dead moss usually does not all come off in the first rinse. ARMA says moss “will loosen over time and may be removed with a leaf blower,” and that severe cases may take more than one bleach treatment.

Why Moss Matters

Moss on asphalt shingles is more than a cosmetic problem. ARMA says that, unlike algae, moss “can be detrimental to asphalt shingle performance.” The mechanisms ARMA and GAF describe:

• Lifted shingle edges. ARMA says moss can cause the leading edges of shingles to lift or curl, which increases the risk of shingle blow-off in wind.
• Moisture and leaks. ARMA says severe moss build-up can cause lateral water movement, leading to moisture damage to the roof deck or even leaks. GAF notes that moss absorbs and holds water against the roof.
• Granule loss. GAF says retained water can degrade shingles over time and cause them to lose the granules that protect against UV.

No manufacturer or ARMA document we reviewed puts a percentage on how much moss shortens shingle life, so we do not give one. How much damage occurs depends on how long the moss has been there and how thick it is.

Moss is most common on shaded, damp roofs, which is why it shows up most often in wet, tree-covered regions such as the Pacific Northwest. ARMA notes that in North America moss tends to grow on north-facing roof planes, which stay damp longer. Dry, sunny climates see far less moss but can still see algae streaks.

For the bigger picture on shingle service life and what shortens it, see our asphalt shingle roof lifespan guide.

Why You Cannot Pressure-Wash an Asphalt Shingle Roof

Pressure washing is the wrong tool for moss removal on asphalt shingles. Every source we reviewed says so:

• ARMA: “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’s current bulletin also says not to use any type of brush or broom on algae.
• GAF (TAB-R-102, 9/19/2024): pressure washing “may dislodge granules, which can lead to premature shingle failure.”
• CertainTeed (Shingle Applicator’s Manual): high-pressure washing “should never be used for algae removal” because it can remove granules and shorten roof life.
• Owens Corning: its algae guidance says not to scrub or use high-pressure power washing equipment, and its Standard Product Limited Lifetime Warranty (Pub. No. 10023873-I, August 2026) excludes damage caused by “power washing.”

Granules shield the asphalt from UV, which is why ARMA ties pressure washing to premature roof failure. Stick with garden-hose pressure and the soft-wash method. For the full cleaning method, including every maker’s mixing ratio, see our guide on how to clean an asphalt shingle roof.

If this, then that: choosing the removal route

If your roof is	Then	Basis
Asphalt shingle, light moss, walkable from a ladder	Soft-wash with the maker’s bleach recipe, 15 to 20 minutes, low-pressure rinse	ARMA, GAF, Owens Corning, CertainTeed
Asphalt shingle, heavy moss with lifted edges	Treat, then get a roofer to inspect for repairs	ARMA: lifted edges raise blow-off risk
Steep pitch or two stories or taller	Hire a pro with fall protection	OSHA 6-foot threshold for workers
Existing roof, zinc or copper strips proposed	Decline; reserve for the next reroof	ARMA: exposed nails or broken sealant bonds
Roof due for replacement, moss-prone lot	Specify algae-resistant shingles and trim trees	Owens Corning: AR does not address moss

Step 1: Soft-Wash Application

The right mix depends on what you use. ARMA’s position is that bleach and water is “the most effective method of cleaning algae and moss from a roof,” and that other chemicals should be cleared with your shingle maker first. ARMA’s roofing manual warns that some commercially available moss and algae chemicals “may contribute to rapid roof system failures.”

Option	Active ingredient	Mixing	Time on the roof	Source
Bleach (ARMA)	Sodium hypochlorite	50:50 laundry-strength bleach and water	15 to 20 minutes; do not let it dry	ARMA, Algae and Moss Prevention and Cleaning
Bleach (GAF)	Sodium hypochlorite	1 gallon bleach, 4 gallons water, 1 cup TSP or a phosphate-free substitute	Up to 20 minutes	GAF TAB-R-102
Bleach (Owens Corning)	Sodium hypochlorite	1 gallon bleach to 1 gallon water	About 10 to 20 minutes	Owens Corning algae guidance
Bleach (CertainTeed)	Sodium hypochlorite	1 part bleach to 3 parts water, pinch of TSP	Not stated	CertainTeed Shingle Applicator’s Manual
Branded moss and algae cleaners (for example Wet & Forget, Spray & Forget, Safer’s)	Varies by product; check the label	Per label	Per label	CertainTeed’s manual names Safer’s Moss and Algae Cleaner and Shingle Shield Roof and Deck Cleaner; ARMA says to ask your shingle maker first
Zinc sulfate moss products	Zinc sulfate	Per label	Per label	ARMA: contact your shingle maker before using moss control chemicals

Application:

1. Work in cool, overcast, calm conditions. ARMA says not to let the bleach solution dry on the roof, because that may prevent complete rinsing.
2. Protect plants first: cover vegetation under the eaves before spraying, then flush it with plain water afterward (Owens Corning). GAF says, “Be sure to protect any shrubs below.”
3. Apply with a pump sprayer from a ladder or walkboards. ARMA says the solution “should be gently dispersed on the roofing surface” and advises working from a ladder or walkboards where possible.
4. Wet the moss evenly. Do not scrub.
5. Wear eye protection and rubber gloves, as ARMA advises for bleach. Never mix bleach with ammonia, vinegar or other cleaners.

All four sources in the table publish a bleach method (ratios from 1:3 to 1:1 bleach to water). Bleach runoff harms plants, so cover and rinse them. For a branded cleaner, confirm the label lists asphalt shingles and that your shingle maker does not object.

Step 2: Let It Work (Do Not Over-Dwell Bleach)

Bleach does not need hours on the roof. ARMA’s current technical bulletin says the solution “should be left on the roof for at least 15 minutes but no more than 20 minutes.” GAF says up to 20 minutes, and Owens Corning says about 10 to 20 minutes. ARMA’s 2012 guidance allows extended dwell times if needed, but says to avoid letting the solution dry completely. Leaving bleach on for many hours is not in any maker’s instructions and puts more chemical onto plants and anyone below.

The moss will still be on the roof at minute 20: the goal is to kill it, then let rain and a leaf blower carry it off over the following weeks, as ARMA describes. For branded products, follow the label on wait time and rinsing.

Stay off the treated area. ARMA warns that the application and rinse process will make the roof slippery and potentially hazardous to walk on.

Step 3: Gentle Rinse from Above

When the dwell time is up, rinse with a standard garden hose at low pressure. ARMA says to “rinse thoroughly with low pressure water,” and GAF’s bulletin says to rinse with low-pressure water.

Rules:

• Spray downhill. Rinse from the ridge toward the eaves. Spraying upward against the shingles can cause them to lift and possibly warp, according to a GAF RoofViews article.
• Use a wide spray pattern, not a jet. The aim is to carry the solution off, not to blast moss loose.
• Skip the scrub brush. ARMA warns that scrubbing “may loosen and remove granules.”
• Rinse plants again. Flush shrubs and beds below with plain water after the roof rinse, as Owens Corning advises.

Some dead moss will stay attached for weeks. ARMA says it will loosen over time and can be cleared with a leaf blower, with the air aimed down the slope so debris is not driven under shingle edges. Do not pry or scrape stubborn patches.

Products: What the Manufacturers Name

The only method that appears in every maker’s guidance is bleach and water applied and rinsed at low pressure. Among branded products, CertainTeed’s Shingle Applicator’s Manual names Safer’s Moss and Algae Cleaner and Shingle Shield Roof and Deck Cleaner as options for lightening discoloration on shingles that are not algae-resistant. Our ranking of the best roof cleaner products checks each one against that guidance.

Other popular products, such as Wet & Forget and Spray & Forget, are sold for roof moss and algae, but none of the ARMA, GAF, Owens Corning or CertainTeed documents we reviewed names them. ARMA’s guidance is to ask your shingle maker before using any commercial moss or algae chemical. For ranked products checked against that guidance, see our best roof moss killer comparison.

The strongest published recipes are 1:1 (ARMA’s 50:50 and Owens Corning’s 1 gallon of bleach to 1 gallon of water). A contractor proposing anything stronger, such as undiluted commercial sodium hypochlorite, should name in writing whose instructions they are following.

Zinc and Copper Strips: Only When You Reroof

Zinc and copper strips work on the same idea as algae-resistant shingles: rain washes metal ions down the roof, which discourages growth. CertainTeed’s manual notes that zinc and copper oxide granules have both been used in algae-resistant shingles, and Owens Corning says experts noticed that algae staining was reduced below metal vents and flashing.

The catch is installation on a roof that is already in place. ARMA’s guidance is direct: “Adding zinc or copper strips to an existing roof is not recommended since this will require either applying the strips with exposed nails (which can cause leaks over time) or breaking the sealant bond (which may eventually result in wind damage) to slide the strips under the shingles.” That rules out lifting ridge cap shingles or field shingles to slip strips underneath.

ARMA says strips, or shingles with algae-resistant copper granules, “may be employed when it is time to replace a roof.” If you want strips on your current roof anyway, ask your shingle manufacturer in writing whether the method affects your wind or leak coverage.

Algae-Resistant Shingles at Replacement

When the roof is due for replacement, algae-resistant shingles are the maker-backed prevention option. GAF uses Time-Release Algae-Fighting Technology, Owens Corning uses StreakGuard, and CertainTeed uses StreakFighter, all based on copper-bearing granules. Owens Corning notes that its AR products do not address green algae or moss, so shade and debris control still matter on a moss-prone roof.

Trimming Trees: The Light + Moisture Factor

Moss needs shade and moisture. ARMA lists these prevention steps for an existing roof:

• Trim tree branches back so more sunlight reaches the roof and less debris falls on it.
• Clear debris regularly with a leaf blower or similar non-abrasive method, aiming the air down the slope.
• Keep gutters clean so water drains properly.
• Do not let an upper roof’s downspout drain onto a lower roof. Extend it into the lower gutter.

Pay particular attention to north-facing slopes, which ARMA and GAF both identify as the most likely to stay damp. Tree work near a roof or power lines is a job for a licensed, insured arborist.

Oregon State University Extension, writing about moss on Pacific Northwest roofs, calls trimming nearby trees so more sun reaches the roof the most effective long-term solution: “You’ve got to let the sun in or it will return.” For annual upkeep, see our roof maintenance schedule and gutter guide.

Cleaning Gutters After Moss Removal

After moss removal, the gutters will hold dead moss, granules and debris. Clean them out:

• Dead moss can clog gutters and downspouts, causing overflow that damages fascia and siding.
• Granules in gutters can be a sign of roof wear. Photograph and date what you find so you can track it over time.
• Standing water in clogged gutters keeps the roof edge damp, which favors new growth.

Some moss removal companies include gutter cleaning in the price. Ask explicitly when you compare quotes.

When to Hire a Pro

Moss removal is DIY-friendly only within limits. ARMA recommends that only trained professionals work on roofs. Hire a pro when:

• The roof pitch is steep. A treated roof is slippery, and you should not need to walk on it.
• The roof is two stories or taller. You cannot treat it safely from a ladder.
• The moss is heavy and has lifted shingle edges. The roof may need an inspection and repairs after treatment.
• Your algae-resistant shingles are still under an algae warranty. Call the manufacturer before paying anyone (see the warranty section below).

For pricing by method, roof type and pitch, see our roof moss removal cost guide. Ask each contractor to name the chemical and dilution (50:50 is ARMA’s bleach ratio), a rinse at garden-hose pressure, and their fall protection setup.

OSHA 29 CFR 1926.501(b)(13) requires employers to protect workers engaged in residential construction activities 6 feet or more above a lower level with guardrails, safety nets or personal fall arrest, unless they can show those are infeasible. A crew on a wet, treated roof without a harness and anchor is cutting corners.

Manufacturer Warranty Considerations

The major shingle makers publish their own cleaning guidance. Damage from methods outside that guidance may not be covered. What each one says:

Manufacturer	Pressure washing	Cleaning chemicals	Algae-resistance program	Source
GAF	Do not power wash; may dislodge granules and lead to premature shingle failure	Publishes a bleach, water and TSP recipe	StainGuard (10-year), StainGuard Plus (25-year) and StainGuard Plus PRO (30-year) algae protection limited warranties on qualifying products	GAF TAB-R-102 (9/19/2024)
Owens Corning	Warranty excludes damage caused by power washing	Warranty excludes damage from cleaning solutions “not in accordance with our algae removal instructions”	StreakGuard; 25-year AR coverage with approved hip and ridge shingles; does not cover moss, lichen or green algae	Owens Corning warranty Pub. No. 10023873-I (August 2026)
CertainTeed	High-pressure washing “should never be used for algae removal”	Names Safer’s, Shingle Shield or a 1:3 bleach mix	StreakFighter; 10 or 15 year algae warranty depending on product	CertainTeed Shingle Applicator’s Manual; CertainTeed AR shingle page

Algae resistance is not moss resistance. These programs target the blue-green algae Gloeocapsa magma, and Owens Corning states plainly that its algae-resistant products do not address moss. Read your own warranty for its exact terms and exclusions.

Keep the product label, the dilution you mixed (for example 50:50 for ARMA’s recipe) and dated photos in your roof file. If you ever file a warranty claim, they show you followed the maker’s cleaning instructions.

Insurance and Algae Streaks (Cosmetic Only)

Algae streaks and moss are different organisms with different implications:

• Algae streaks (Gloeocapsa magma). ARMA says there is no scientific evidence that algae damages asphalt shingles, and Owens Corning says it has not seen evidence that algae affects shingle performance. Removal is mostly about appearance.
• Moss. ARMA says moss can lift shingle edges and, in severe cases, cause leaks. Removal is about function as well as appearance.

Homeowners policies generally treat moss removal and algae cleaning as maintenance, not a covered peril, and commonly exclude damage traced to long-term neglect. Policy wording decides.

If years of moss have already lifted shingle edges, see signs you need a new roof and the new roof cost guide.