Black streaks on asphalt shingles are commonly algae, not dirt.[1] This page separates algae, moss and lichen. It also covers what cleaning is safe and what can hurt your warranty.
Short answer
Fairfield Peak Roofing is a referral service. We do not clean roofs or do any roofing work. We connect Ohio homeowners with independent local contractors. This page is neutral research to help you judge a contractor's plan.
Last reviewed: September 28, 2026. Sources are listed at the end, with the date each was checked.
Algae vs. Moss vs. Lichen: What Is on Your Roof?
The three growths differ in cause, damage and coverage. Identify yours before you pick a fix.
| Question | Algae | Moss | Lichen |
|---|---|---|---|
| What is it? | Mostly a blue-green alga. Gloeocapsa magma is probably the most common.[2] | A moisture-loving plant. It thrives on north-facing slopes with less sun.[1] | A fungus partnered with an alga or cyanobacterium.[6] |
| Distinguishing sign | Black streaks. Often mistaken for mold or mildew.[1] | Raised growth. Can make shingle leading edges lift or curl.[1] | A separate organism from moss. Get it identified in person.[7] |
| Documented harm | Staining. ARMA says cleaning is only temporary.[2] | Edge lift raises blow-off risk.[1] It also slows water flow off the roof.[7] | OSU Extension says lichens do not damage plants.[6] Oregon State says they do not add to composite shingle damage.[7] |
| Warranty angle | Algae-resistant shingles carry a separate algae warranty.[3][4] | Not named in the algae warranties checked.[3][4] | Owens Corning excludes lichen discoloration.[3] |
Two limits apply here. First, no shingle-maker source on lichen damage to asphalt was found. Second, ARMA gives no separate lichen method in the pages reviewed.
If you see more than one type, expect a mixed answer. A contractor should name each growth and explain the plan for each.
What Not to Do
- Pressure washing. ARMA says never use a pressure washer, because it causes granule loss.[1] Owens Corning lists power washing among post-install changes its warranty excludes.[3]
- Brushes and brooms. ARMA says not to use any brush or broom on algae.[2] Scrubbing can loosen and remove granules.[2]
- Zinc or copper strips on an existing roof. ARMA does not recommend them there, citing leak and wind damage risks.[1] Oregon State calls them not effective to eliminate moss.[7] It adds that zinc and copper harm aquatic life.[7]
- Mixing bleach with other cleaners. Bleach with ammonia makes toxic chloramines. Bleach with acids releases chlorine gas.[8] Vinegar and rust removers count as acids.[8]
- Walking a wet, growth-covered roof. This is a general safety judgment, not a measured statistic. A slip is far worse than a stain.
The Oregon State page also mentions scraping moss with a putty knife. That is general advice, not asphalt-specific. ARMA's warning about abrasion is the safer guide for shingles.[1][2]
What ARMA Actually Says About Cleaning
ARMA is the Asphalt Roofing Manufacturers Association. It publishes two pages that matter here, and they differ slightly.
| Topic | ARMA page 1: prevention and cleaning[1] | ARMA page 2: discoloration bulletin[2] |
|---|---|---|
| Mix ratio | 50:50 laundry-strength liquid chlorine bleach and water | Names bleach and water but gives no ratio. Says directions vary among manufacturers. |
| Dwell time | 15 to 20 minutes, then low-pressure rinse | At least 15 minutes, no more than 20 |
| Scrubbing | Not addressed in the summary reviewed | Avoid. Friction may remove granules. |
| Power washer | Never use | Do not use a power washer, brush or broom |
| Result | Called the most effective method | Only temporary. Discoloration may recur. |
The documented steps, if a contractor uses bleach
- Mix 50:50 laundry-strength liquid chlorine bleach and water, per ARMA's current page.[1]
- Apply and leave it 15 to 20 minutes.[1][2]
- Rinse at low pressure. Do not use a power washer, brush or broom.[1][2]
- Never mix bleach with ammonia or acids. Both mixes release toxic gas.[8]
- Expect the result to be temporary. ARMA says discoloration may recur.[2]
Roof work carries fall risk. Most homeowners should hire it out and ask for the warranty check below first.
Neither page addresses plants near the house. No reviewed source gives a plant-safe rinse method.
Ask any contractor how they protect landscaping. CDC says hypochlorite breaks down in air.[9] It does not build up in the food chain.[9]
That does not make it harmless to your shrubs.
Owens Corning's warranty excludes damage from applying cleaning solutions after installation.[3] That sits in tension with ARMA's bleach method. Ask the shingle maker in writing before any chemical cleaning.
Warranty Check: What Two Makers Actually Cover
| Maker | Algae warranty term | What it covers | Limits to note |
|---|---|---|---|
| Owens Corning (2020 standard warranty copy)[3] | 10 years on most lines. 15 years on Berkshire. AR is regional. | Brown-black staining from Gloeocapsa magma | Excludes lichen, mold and green algae. After year one, labor is not covered and payout is prorated. Excludes power washing and cleaning-solution damage. |
| CertainTeed algae-resistant shingles[4][5] | 10 or 15 years, depending on product | Blue-green algae contamination. Pays to replace or clean affected shingles. | Full terms sit in its separate shingle warranty. That document was not reviewed. |
GAF's warranty pages could not be loaded. Read your own paperwork. Terms change by product line and year. Our roof warranty guide covers how to read the fine print.
Algae-Resistant Shingles: What They Do and Do Not Do
Algae-resistant shingles use copper-containing granules. The copper releases gradually over time.[5] ARMA lists them as a prevention option.[1]
The warranty language is narrow. It targets algae staining only. Owens Corning excludes lichen and green algae.[3] Neither maker's page reviewed promises moss control.
No independent test on how long the copper keeps working was found. Treat the warranty term as a legal period, not a measured performance life.
How Fast Does Growth Happen in Ohio?
Nobody has published a growth rate for Fairfield County roofs that this page could find. Here is what is and is not backed.
| Claim | Status |
|---|---|
| Humid climates favor algae | Supported by ARMA.[1] |
| Moss favors shade and north-facing slopes | Supported by ARMA and Oregon State.[1][7] |
| Tree debris holds moisture on the roof | Supported by ARMA.[1] |
| Months or years until visible growth in Ohio | Not measured in any source reviewed. |
| Local humidity, canopy or freeze-thaw counts | Not verified for this page. |
| Years of life lost to algae or moss | Not measured in any source reviewed. |
The practical takeaway is simple. Shade and trapped moisture are the documented drivers. A shaded north slope is the first place to look. Our news piece on Ohio roof algae covers the same pattern.
When Growth Means Get an Inspection
These are inspection cues, not results from a cited study. They come from the documented effects above.
- Shingle edges that look lifted or curled from the ground.[1]
- Growth that blocks water flow toward the eaves.[7]
- Staining or damp spots in the attic below a mossy slope.
- An older roof already near the end of its service life.
Cleaning a failing roof wastes money. An inspection tells you whether to clean or replace. See signs you need a new roof and the roof lifespan guide. Winter freezing adds stress, so also read about ice dams.
Questions to Ask a Contractor
This page gives no dollar figures. No published cost guide worth citing was found. Get itemized quotes and ask these.
- Which growth do I have: algae, moss, lichen or a mix?
- What exact product and mix ratio will you use?
- How does that match my shingle maker's cleaning guidance?
- Will you avoid pressure washing and brushes?
- How will you protect my plants, gutters and downspouts?
- How long until the dead growth washes away, and is a second pass included?
- What does the quote say if the growth returns?
- Do you carry insurance for work on the roof?
- Will the work affect my shingle or algae warranty in writing?
Fairfield Peak Roofing connects homeowners with local contractors. Use the contractor directory or the contact form to request an estimate. Contractors set their own prices and terms.
Frequently Asked Questions
Will bleach damage my asphalt shingles?
ARMA describes bleach and water as an effective cleaning method. It warns against scrubbing and pressure. Owens Corning excludes damage from cleaning solutions in its warranty. Ask your shingle maker before applying anything.
How long does dead moss or algae take to wash off?
No source gives a reliable timeline. Ask your contractor what to expect for your roof.
Is it safe to walk on a mossy or algae-covered roof?
Avoid it. This is a general safety judgment, not a statistic. Wet growth is slippery. Hire a contractor with fall protection for anything beyond ground reach.
Do zinc or copper strips work?
Sources disagree. ARMA does not recommend them on existing roofs.[1] Oregon State says they do not eliminate moss.[7] Ask a contractor for evidence for your roof type.
Does homeowners insurance cover moss damage?
Policy wording varies, and Ohio policy language was not verified. Ask your agent. Read the maintenance and wear sections of your own policy.
How often should I check my roof for growth?
No source sets a schedule. A look from the ground after wet seasons is a reasonable habit. Watch shaded and north-facing slopes first.
How This Page Was Researched
Fairfield Peak Roofing Team compiled this page from the sources below. Each was opened and read on September 28, 2026.
The Owens Corning warranty is a 2020 copy, so current terms may differ. GAF pages returned access errors and are not used. No expert reviewed this page. It is not professional roofing advice. It does not replace your shingle warranty or an on-site inspection.
Sources
- ARMA, Algae & Moss Prevention and Cleaning for Asphalt Roofing Systems. Checked September 28, 2026.
- ARMA, Algae Discoloration of Roofs (technical bulletin). Checked September 28, 2026.
- Owens Corning, Standard Product Limited Warranty brochure, 2020 copy hosted by a distributor: PDF. Checked September 28, 2026. Current terms may differ.
- CertainTeed, Algae Resistant Shingles. Checked September 28, 2026.
- CertainTeed, StreakFighter Algae-Resistant Technology. Checked September 28, 2026.
- Ohio State University Extension, Lichens (Ohioline fact sheet). Checked September 28, 2026.
- Oregon State University Extension, Moss on Roofs & Walkways. Checked September 28, 2026. Oregon climate, general guidance.
- Washington State Department of Health, Dangers of Mixing Bleach with Cleaners. Checked September 28, 2026.
- CDC ATSDR, ToxFAQs: Calcium Hypochlorite / Sodium Hypochlorite. Checked September 28, 2026.
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