Asphalt Shingle Cleaner: Removing Black Streaks and Moss Without Wrecking the Roof

The right asphalt shingle cleaner is a low-pressure, roof-safe product that kills the algae, moss or lichen and lets rain rinse the residue away over time. Most black streaks on shingles are algae, and they usually respond to a sodium hypochlorite (bleach-based) wash or a slower-acting ready-to-use cleaner. Thick moss needs gentle removal plus a treatment. What you should avoid is pressure washing, scrubbing hard and walking on the roof without fall protection, because those strip granules, void warranties and cause injuries. When the roof is steep, high or fragile, hiring a soft-wash roof cleaning pro is the safer call.

Shingle color and heat →

What's Growing on Your Shingles?

Growth	Looks like	Typical treatment
Algae (often Gloeocapsa magma)	Dark streaks running down the roof, often on shaded or north-facing slopes	Soft wash with a diluted bleach-based cleaner or a roof-labeled algae cleaner
Moss	Green, fuzzy clumps, often along edges and in shaded valleys	Gentle removal by hand from a ladder or with a soft brush, then a moss treatment
Lichen	Crusty, flat, gray-green spots that cling tightly	Treatment and patience; lichen releases slowly and shouldn't be scraped
Dirt and debris stains	Brown or gray patches under trees	Rinse with a garden hose and clean the gutters

Algae streaks are mostly cosmetic, though they can make a roof absorb more heat. Moss and lichen matter more, because they hold moisture against the shingles and can lift edges over time.

Types of Asphalt Shingle Cleaners

• Sodium hypochlorite (bleach) mixes: the traditional soft-wash approach. A diluted bleach solution, often with a surfactant to help it cling, kills algae quickly and lightens streaks within minutes to hours. It's also harsh on plants, metals and your skin.
• Oxygen bleach (sodium percarbonate) cleaners: gentler on plants and surfaces, usually slower acting, and often needing a light brush or more dwell time.
• Ready-to-use "spray and walk away" cleaners: hose-end products you spray on and let weather clean the roof over weeks or months. Easy and low risk, but slow.
• Zinc- or copper-based moss treatments: aimed mainly at moss and lichen. Check labels carefully, because some are restricted near waterways.

Read the label for roofing use, and check your shingle manufacturer's guidance. Several shingle makers publish cleaning recommendations, and some warn that certain chemicals or methods can affect warranty coverage. A hose-end roof cleaner labeled for asphalt shingles is the easiest place to start for mild streaking.

How to Clean Asphalt Shingles Safely

1. Decide if you should do it yourself. A low-slope, single-story roof is a different job from a steep two-story roof. Falls from roofs cause serious injuries every year. If you aren't comfortable with ladders and fall protection, hire a pro.
2. Pick a cool, calm, overcast day. Cleaners dry too fast in hot sun, and wind carries spray onto plants and cars.
3. Protect plants and surfaces. Wet down landscaping, cover delicate plants with plastic sheeting, and rinse them again after.
4. Apply from the top down with low pressure. A pump sprayer or hose-end sprayer is enough. The goal is to wet the growth, not blast it.
5. Let it dwell. Follow the label. Many bleach-based mixes work in 15 to 30 minutes; oxygen and spray-and-leave products take longer.
6. Rinse gently if the label calls for it. Use a garden hose, not a pressure washer, and rinse plants and siding below.
7. Clean up gutters and downspouts. Dead growth and granules collect there.

A basic 2-gallon pump sprayer handles most DIY roof applications, and chemical-resistant gloves and eye protection are a must with bleach mixes.

Why Not Pressure Wash a Shingle Roof?

Asphalt shingles are covered with mineral granules that protect the asphalt from UV and give the roof its color. High-pressure water knocks those granules loose, can drive water under shingle tabs, and can break seal strips. The roof may look clean for a season and then age faster. Many manufacturers and roofing associations advise against pressure washing shingle roofs. Soft washing, which relies on chemistry at low pressure, is the widely recommended approach. Pressure washing still has its place on pavement, and our pressure washing cost calculator is for that kind of job, not the roof.

Dealing With Moss and Lichen

• Knock off loose moss by gently brushing downward, in the direction the shingles overlap, never upward.
• Apply a moss treatment and give it time. Dead moss often releases on its own as it dries.
• Leave stubborn lichen alone after treatment; scraping pulls granules off with it.
• Trim overhanging branches to let in sun and air, which moss dislikes.

Protecting Everything Below the Roof

Runoff from a roof wash lands on gutters, siding, plants and often the driveway. Bleach solutions can stress or kill plants, discolor some metals, and leave marks on pavement. Rinse plants before and after, and consider directing downspouts onto a lawn area you've wetted rather than into garden beds. If runoff reaches your asphalt, rinse it; our guide on bleach on an asphalt driveway explains what diluted bleach does to pavement and how to limit marks. Keep kids and pets away until everything is rinsed and dry.

Keeping Streaks and Moss From Coming Back

• Zinc or copper strips: installed near the ridge, they release metal ions when it rains that can slow algae and moss below them. Results vary with roof pitch, rainfall and distance from the strip.
• Algae-resistant shingles: many modern shingles include copper-coated granules. If you're re-roofing in a humid climate, it's worth asking about. Our piece on black asphalt shingles covers how color and granules affect streak visibility and heat.
• More sun and airflow: trim trees and clear debris that keeps the roof damp.
• Clean gutters: overflowing gutters keep edges wet.
• Periodic light treatments: a spray-and-leave product every year or two can keep new growth from taking hold.

Pre-cut zinc roof strips are sold in rolls for DIY installation, though fastening them properly means working on the roof, so the same safety rules apply.

DIY vs Hiring a Soft-Wash Pro

Factor	DIY	Pro soft wash
Safety	You manage ladder and roof risk	Crew with fall protection and insurance
Speed of results	Fast with bleach mixes, slow with spray-and-leave	Usually same day
Plant and property protection	Up to you	Should be part of the service; ask how they handle it
Cost	Cleaner and sprayer	Varies widely by roof size, pitch and region

When getting quotes, ask what chemicals and pressure the company uses, how they protect landscaping, and whether their method follows your shingle maker's guidance.

Bottom Line on Asphalt Shingle Cleaners

For most black streaks, a roof-labeled cleaner applied at low pressure, either a diluted bleach-based soft wash or a slower spray-and-leave product, does the job. Treat moss gently, never pressure wash shingles, protect plants and pavement from runoff, and hand steep or high roofs to a soft-wash pro. Zinc strips, trimmed trees and algae-resistant shingles help keep the roof clean longer.