Dark streaks, green patches, and thick moss can make a residential roof look much older than it really is. In Michigan, shaded sections of roof shingles may stay damp after rain, melting snow, or morning dew, creating favorable conditions for moss and algae.

Homeowners in Saginaw, Bay City, Midland, Lansing, Mt. Pleasant, West Branch, Cadillac, Traverse City, Gaylord, and Harbor Springs may notice the heaviest growth on north-facing roof slopes or beneath overhanging trees.

The most effective products for cleaning asphalt roof shingles are manufacturer-approved, low-pressure treatments designed to kill organic growth without scrubbing away protective granules. Depending on the shingle brand and type of growth, this may include a properly diluted sodium hypochlorite solution, a bleach-free concentrate labeled for asphalt roofing, or a no-rinse biocide.

The right product depends on the cleaner’s label, the shingle manufacturer’s instructions, the condition of the roof, and the surrounding landscaping.

KEY TAKEAWAYS

• Use only products that specifically list asphalt roof shingles as an approved surface.
• Never use a pressure washer, stiff broom, wire brush, or aggressive scrubbing on roof shingles.
• Black streaks are usually algae, while thick, raised growth is more likely moss or lichen.
• Protect plants, gutters, siding, and runoff areas before applying any chemical treatment.
• If roof shingles are curled, cracked, loose, leaking, or heavily deteriorated, cleaning will not solve the underlying problem.

Why Do Moss and Algae Grow on Roof Shingles?

Black streaks on roof shingles are commonly caused by blue-green algae, often identified as Gloeocapsa magma. GAF explains that airborne spores can move from roof to roof and that dew provides much of the moisture the organism needs. Growth often becomes more noticeable on northern roof slopes because those areas receive less direct sunlight and dry more slowly.

Moss behaves differently. Instead of creating a flat stain, it forms a thicker layer that can retain moisture against the roofing surface. As moss grows around the edges of roof shingles, it may lift tabs, slow drainage, and allow moisture to remain in areas that should dry quickly.

Lichen can be even harder to remove because it bonds tightly to the shingle surface.

ARMA reports that four out of five homes in the United States are roofed with asphalt shingles. The association also reports that more than 12.5 billion square feet of asphalt shingle products are manufactured annually, enough to cover more than 5 million homes. That widespread use makes proper maintenance especially important because the wrong cleaning process can damage a very common roofing material.

KNOWLEDGE BOX: BLUE-GREEN ALGAE

Blue-green algae are photosynthetic organisms that can create dark brown or black streaks on roof shingles. The staining is often cosmetic at first, but homeowners may confuse it with soot, mold, dirt, or deteriorated roofing materials. A roof inspection can help determine whether the discoloration is surface growth or actual material damage.

Expert insight: ARMA advises homeowners to consult the shingle manufacturer before using any cleaning chemical or method, as approved formulas can vary by product and by the severity of the staining.

What Products Work Best for Removing Moss and Algae From Roof Shingles?

The best roof-cleaning product is not necessarily the strongest chemical on the shelf. It is the product that removes the specific growth while remaining within the roof shingle manufacturer’s instructions.

For many asphalt roof shingles, a low-pressure chemical treatment is safer than mechanical cleaning.

Product Category	Best Use	Main Advantages	Important Limitations
Manufacturer-approved bleach solution	Heavy algae staining and black streaks	Fast acting and supported by some shingle manufacturers	Can harm plants and exterior finishes if mishandled; ratios vary by manufacturer
Eco-friendly or bleach-free concentrate	Light-to-moderate algae, moss, or mildew when the label lists roof shingles	Lower odor and may be easier to use near sensitive landscaping	“Eco-friendly” does not automatically mean harmless; results may take longer
No-rinse biocide	Gradual treatment of moss, algae, or lichen	Minimal rinsing and less physical contact with roof shingles	Dead growth may take weeks or months to weather away
Ammoniated soap formula	Surface soil or organic residue when specifically approved	Surfactants can help the solution spread across roof shingles	Must never be mixed with bleach; may not be approved by the shingle manufacturer

Manufacturer-Approved Bleach Solutions

A diluted sodium hypochlorite solution is one of the most established treatments for algae staining, but homeowners should not assume that a single universal recipe works for every roof.

ARMA states that mixing directions vary among manufacturers. GAF’s technical bulletin, for example, identifies a mixture of:

• 4 gallons of water
• 1 gallon of bleach
• 1 cup of trisodium phosphate or an acceptable phosphate-free substitute

GAF directs users to leave the mixture on eligible roof shingles for up to 20 minutes, then rinse with low-pressure water.

That ratio is manufacturer-specific guidance, not a blanket recipe for every brand of roof shingles. Before using it, confirm the exact shingle manufacturer, review its current technical bulletin and warranty, and follow the cleaner’s product label.

Eco-Friendly and Bleach-Free Concentrates

Bleach-free roof cleaners can be useful when homeowners want less odor or are concerned about landscaping. These products may contain oxygen-based ingredients, detergents, or other active agents to loosen organic stains.

They generally work more slowly than bleach-based treatments and may require repeated applications.

Do not rely on words such as “natural,” “green,” or “eco-friendly” alone. Check whether the label specifically identifies asphalt roof shingles, what organisms the product controls, whether rinsing is required, and how runoff should be handled.

A cleaner can be bleach-free and still irritate skin, damage plants, or affect waterways when used incorrectly.

No-Rinse Biocides

No-rinse products are designed to remain on roof shingles while the weather gradually removes the dead growth. They can reduce the need for aggressive rinsing, but they are not instant cosmetic fixes.

Heavy moss may turn brown after treatment and then slowly release over several weeks or months.

Choose a product labeled for the exact roofing material and target organism. Follow all application rates, temperature restrictions, personal protective equipment requirements, and runoff directions. Applying more product than the label allows will not necessarily yield better results.

KNOWLEDGE BOX: BIOCIDE

A biocide is a substance intended to control or destroy living organisms such as algae, moss, mold, or mildew. Because it is designed to affect living material, its dilution, application, environmental, and personal-safety instructions are important.

Ammoniated Soap Formulas

Some cleaning products combine soaps or surfactants with ammoniated ingredients. These formulas may improve wetting and help loosen surface residue, but they should be used only when both the cleaner’s label and the roof shingle manufacturer permit them.

Never combine an ammoniated product with chlorine bleach. The CDC warns that mixing bleach with ammonia-containing cleaners can release hazardous chloramine gases. Exposure may irritate the eyes and respiratory system and can cause serious lung injury.

Expert insight: GAF and ARMA both emphasize low-pressure application and the avoidance of cleaning methods that remove granules or lift roof shingles. Increasing a product’s strength does not make up for unsafe application.

What Is the Best Way to Remove Black Streaks From Asphalt Shingles?

The best way to remove black streaks is to confirm that they are algae, select a manufacturer-approved cleaning solution, apply it with low pressure, allow the specified dwell time, and rinse only as directed.

Do not try to blast the streaks away.

GAF describes blue-green algae as dark staining that often covers more area near the lower portion of a roof and tapers as it approaches the ridge. Because similar discoloration can come from soot, tree debris, dirt, or material deterioration, homeowners should examine the roof from the ground and consider a professional inspection before treating an unfamiliar stain.

A pressure washer can strip away protective granules, force water underneath shingle edges, and contribute to premature failure. ARMA’s technical guidance states that power washers, brushes, and brooms should not be used to remove algae from asphalt roof shingles.

KNOWLEDGE BOX: SHINGLE GRANULES

Granules are the small mineral particles embedded in the exposed surface of asphalt roof shingles. They protect the asphalt from ultraviolet light, add color, and improve fire and weather resistance. Widespread granule loss is a roofing condition that cleaning cannot reverse.

How Should Roof Shingles Be Cleaned Step by Step?

Roof cleaning combines chemical exposure, slippery surfaces, ladders, and fall hazards. Homeowners should strongly consider hiring a qualified roof-cleaning service rather than walking on the roof themselves.

Herbert Roofing does not perform roof cleaning, but it can inspect roof shingles before treatment to determine whether roof repair or replacement should come first.

Step 1: Put Safety First

Inspect the roof from the ground using binoculars or a camera’s zoom function. Do not climb onto a wet, steep, icy, moss-covered, or damaged roof.

Keep ladders away from power lines, stabilize them on firm ground, and follow all ladder and safety-equipment instructions.

Step 2: Identify the Growth and Inspect the Roof Shingles

Determine whether the roof has:

• Flat black algae streaks
• Raised moss
• Bonded lichen
• Loose leaves or branches
• Actual shingle deterioration

Look for missing tabs, curling edges, cracks, exposed fiberglass mat, damaged flashing, sagging, or soft decking. Schedule a professional roof inspection before cleaning if any of these conditions are present.

Step 3: Remove Loose Debris Without Scrubbing

Clear accessible leaves, branches, and gutter debris from the ground or a properly secured ladder.

Do not scrape attached moss from roof shingles with a wire brush, stiff broom, or metal tool. Thick moss should generally be treated first so it can die and release gradually. A trained service may gently remove loose remnants from a safe position after treatment.

Step 4: Protect Plants and Exterior Surfaces

Move outdoor furniture and vehicles away from the work area and close nearby windows.

Pre-wet grass, shrubs, and garden beds. Temporarily shield sensitive plants when permitted by the cleaning product instructions. Direct runoff away from ponds and other sensitive areas.

Rinse the landscaping promptly after application and remove temporary plant covers before heat builds up beneath them.

Step 5: Apply the Cleaning Solution

Use a garden-style sprayer or another low-pressure applicator specified by the cleaner manufacturer.

Apply an even coating without flooding the joints between roof shingles. Never mix different cleaners, add unapproved chemicals, or exceed the concentration listed on the label.

Step 6: Allow the Product to Dwell

Follow the exact dwell time found in the shingle manufacturer’s technical bulletin and on the cleaner label.

ARMA’s algae guidance says its described treatment should remain on the roof for at least 15 minutes but no longer than 20 minutes before gentle rinsing. GAF’s algae bulletin also specifies a maximum dwell time of 20 minutes for its listed mixture.

Step 7: Rinse Only as Directed

When rinsing is required, use low-pressure water directed down the roof slope. Never spray upward underneath shingle tabs.

Some no-rinse products are intended to remain on roof shingles and continue working over time. Do not rinse those products unless the label specifically instructs you to do so.

Step 8: Recheck the Roof After It Dries

Once the roof has dried, inspect it again from the ground. Moss and lichen may take time to release, so do not repeat the treatment immediately unless the product instructions permit another application.

If discoloration remains because granules are worn, roof shingles are cracked, or the roofing surface has become uneven, the issue may be deterioration rather than organic growth.

Expert insight: GAF recommends having moss removal handled by a professional and warns that rinsing should be done at low pressure and at a downward angle so water does not lift or warp roof shingles.

DIY Roof Cleaning vs. Hiring a Roof-Cleaning Service

A homeowner may be able to handle limited ground-level preparation, but applying chemicals on a sloped roof creates risks that extend beyond ordinary exterior cleaning.

Option	Pros	Cons
DIY roof cleaning	Lower upfront cost and direct control over product selection and timing	Fall risk, chemical exposure, possible warranty issues, and risk of granule loss, plant damage, or water intrusion
Qualified roof-cleaning service	Proper equipment and experience with dwell times, runoff control, and low-pressure application	Higher cost, varying service quality, and a need to verify insurance and cleaning methods

Before hiring a service, ask:

• What product will be applied?
• Is the product approved for your specific roof shingles?
• Will a pressure washer be used?
• How will landscaping and siding be protected?
• Is the company insured?
• How will runoff be controlled?
• Will workers scrub or walk extensively on the shingles?

Reject any proposal that depends on high pressure or aggressive brushing.

KNOWLEDGE BOX: SOFT WASHING

Soft washing is a low-pressure cleaning method that relies primarily on a chemical treatment rather than water pressure. The term alone does not guarantee safety. The product, dilution, application direction, pressure, and technician’s experience determine whether the process is appropriate for asphalt roof shingles.

Expert insight: ARMA encourages the use of trained professionals because the cleaning treatment makes roof shingles slippery and potentially hazardous to walk on.

How Can Homeowners Prevent Moss and Algae From Returning?

Cleaning is usually temporary when the roof shingles remain shaded and damp. Prevention focuses on improving drying conditions, controlling debris, and selecting algae-resistant materials when replacement becomes necessary.

Trim Overhanging Tree Branches

Prune branches that heavily shade the roof or drop leaves and needles onto it. Maintain appropriate clearance without damaging healthy trees.

Additional sunlight and airflow can help roof shingles dry faster after rain, snowmelt, or morning dew.

Keep Gutters and Roof Valleys Clear

Clogged gutters can cause water to back up near the roofline, while debris in the valleys slows drainage.

Clean gutters regularly and make sure downspouts carry water away from the foundation. After severe weather, inspect for branches and leaf piles from the ground.

Consider Zinc or Copper Prevention Products

Zinc or copper strips installed near the ridge can release small amounts of metal ions during rainfall, helping inhibit future organic growth.

These products must be installed correctly so that fasteners and flashing do not create leak points. They are preventive accessories, not repairs for damaged roof shingles.

Choose Algae-Resistant Roof Shingles During Replacement

Modern GAF shingles with StainGuard technology and CertainTeed shingles with algae-resistant granules are designed to inhibit the growth of blue-green algae.

GAF currently lists algae-protection limited warranties of 10, 25, or 30 years, depending on the eligible shingle product and package labeling.

Algae-resistant roof shingles do not eliminate the need for maintenance, but they can provide additional protection for homes surrounded by trees or located in areas where roofs dry slowly.

Expert insight: ARMA recommends considering algae-resistant asphalt roof shingles when reroofing a home that is vulnerable to recurring discoloration.

When Is Cleaning Not Enough for a Residential Roof?

Cleaning can improve appearance and remove organic growth, but it cannot restore missing granules, seal a leak, flatten curled roof shingles, repair flashing, or replace decayed decking.

If the roof has physical damage, address that problem before applying a cleaner.

Roof Repair May Be Appropriate When:

• Damage is confined to a small area.
• A few roof shingles are missing, cracked, or lifted.
• Flashing around a chimney, vent, or skylight is loose or deteriorated.
• A leak has a single identifiable source, and the surrounding roof remains sound.
• Moss has lifted a limited number of tabs, but the roof system is otherwise serviceable.
• Storm damage has affected only one slope or section.

Roof Replacement May Be the Better Choice When:

• The roof is 20 years old or older and shows widespread wear.
• Roof shingles are curling, cracking, blistering, or losing granules across multiple slopes.
• The home has recurring leaks or water stains in several areas.
• The roof deck feels soft or visibly sags.
• Repeated repairs are no longer providing dependable protection.
• Organic growth has contributed to widespread lifting or moisture damage.

Herbert Roofing’s roof replacement guidance lists a roof age of 20 years or more, cracked or missing roof shingles, and interior water stains among the warning signs that replacement may be necessary.

Our repair services address localized problems such as storm damage, missing shingles, flashing issues, leaks, ice-dam damage, and ventilation concerns.

Homeowners comparing new GAF shingles and CertainTeed shingles should consider more than color. Algae resistance, impact rating, wind coverage, underlayment, flashing, ventilation, installation quality, and warranty eligibility all affect long-term performance.

Expert insight: NRCA advises property owners to assess storm damage from the ground and leave close inspection and repairs to a professional roofing contractor.

What Is Roof Maintenance, and How Often Should a Roof Be Inspected?

Roof maintenance is the routine process of inspecting the roofing system, correcting minor defects, managing debris and drainage, and addressing damage before it reaches the home’s interior.

It includes much more than cleaning visible stains from roof shingles.

Timing	Recommended Action
Spring	Check for winter damage, ice-dam effects, loose flashing, debris, and gutter problems
Fall	Clear leaves, examine roof shingles from the ground, and prepare gutters for snow and ice
After severe weather	Look for missing shingles, fallen branches, displaced flashing, hail damage, or new leaks
At least annually	Schedule a professional inspection, especially for older roofs or roofs with previous repairs
Before cleaning	Confirm that the roof shingles are stable enough for treatment and identify warranty restrictions

NRCA recommends inspecting roofing systems at least twice per year, preferably in the spring and fall, with additional inspections after severe weather.

Herbert Roofing recommends at least one professional roof inspection per year for ongoing maintenance. Older roofs, roofs with previous leaks, and roofs exposed to severe weather may need more frequent professional attention.

Expert insight: Regular inspections can identify cracked, warped, or missing roof shingles, deteriorated flashing, and excessive granule accumulation before a homeowner first discovers the problem through an active leak.

Protect Your Roof Before You Clean It

The most effective products for removing moss and algae from roof shingles are low-pressure treatments applied according to the roofing manufacturer’s instructions.

A chemical may remove stains, but only a sound roofing system can protect the home beneath it. Before applying any product, confirm the type of growth, review the label, protect surrounding property, and ensure the roof does not already require repair.

Herbert Roofing does not offer roof cleaning. However, homeowners throughout Mid-Michigan and Northern Michigan can contact Herbert Roofing for residential roof inspections, repairs, and replacement guidance.

If cleaning will not be enough, an experienced roofing team can explain whether a targeted repair or complete roof replacement will provide a better long-term result.

Frequently Asked Questions

What chemicals are safe for cleaning a roof?

The safest choice is a cleaner specifically labeled for asphalt roof shingles and permitted by the shingle manufacturer. Some manufacturers approve a diluted sodium-hypochlorite solution, while other situations may call for a bleach-free or no-rinse product. Never mix chemicals or exceed the concentration on the label.

What is the best way to remove black streaks from asphalt shingles?

Confirm that the streaks are algae, apply a manufacturer-approved solution at low pressure, allow the required dwell time, and rinse gently only when directed. Do not pressure wash or aggressively scrub roof shingles.

Can I pressure wash roof shingles?

No. ARMA and GAF warn that power washing can loosen protective granules, lift roof shingles, and contribute to premature failure. The chemical treatment should perform the cleaning work, not high water pressure.

Are eco-friendly roof-cleaning products effective?

Some bleach-free concentrates can remove light or moderate organic staining, but their performance varies. Choose a product that lists asphalt roof shingles and the target growth on its label. Some products may require additional time or repeated treatment.

How often should I have my roof professionally inspected?

Herbert Roofing recommends at least one professional inspection per year for ongoing maintenance. Homeowners should also perform ground-level checks in the spring and fall and after severe storms. Older roofs or roofs with previous leaks may require more frequent professional attention.

What signs indicate that I need urgent roof repair services?

Active leaks, sagging, soft decking, missing roof shingles, exposed underlayment, damaged flashing, and water entering around chimneys or vents require prompt attention. Cleaning should wait until the roof has been inspected and stabilized.

Should I clean or replace an old roof?

Cleaning may be reasonable when staining is cosmetic, and the roof shingles remain flat, secure, and intact. Replacement may be more appropriate when the roof is at least 20 years old or has widespread cracking, curling, granule loss, repeated leaks, or structural deterioration.