Roofing care & material guide
Black Streaks on Your Roof: Causes, Cleaning and Prevention in Michigan
Black streaks can make a roof look worn before you know whether anything is wrong with the roofing itself. Start by identifying the staining and checking the roof’s condition, then compare the appropriate maintenance or repair options.
This guide focuses on asphalt shingles. If your home has metal, tile or another roof covering, use that product manufacturer’s care instructions.
What causes black streaks on asphalt shingles?
A common cause is Gloeocapsa magma, a cyanobacterium often called blue-green algae. Its dark protective pigment can produce the streaked appearance homeowners notice. Moisture and suitable temperatures support growth; dew can provide that moisture. [1]
Shaded roof areas and north-facing slopes may stay damp longer, but staining is not limited to one side of a home. The pattern is a useful observation to share with a roofing professional, not a complete diagnosis by itself.
How do algae and moss differ?
Algae staining
Often appears as dark streaks or patches. ARMA describes algae primarily as an appearance concern on asphalt shingles; staining alone does not tell you the condition of the rest of the roof.
Moss growth
Moss forms raised growth and can lift shingle edges or interfere with water shedding. It needs its own assessment and an appropriate removal method.
ARMA distinguishes these conditions in its algae and moss guidance. Dirt, debris and other staining can also be mistaken for algae. Avoid identifying every dark mark from color alone. [3]
How should roof algae be cleaned?
Use the shingle manufacturer’s approved method and a qualified professional. ARMA cautions that cleaning can make a roof slippery, that scrubbing may remove granules and that high-pressure washing can damage asphalt roofing. Cleaning may improve appearance, but staining can return. [3]
Before authorizing treatment, ask the cleaner to explain:
- How they identified your shingle product and checked its current cleaning instructions.
- Which treatment and application method they propose.
- How they will protect landscaping, nearby surfaces and drainage areas.
- What result to expect and whether follow-up may be needed.
Cleaning formulas differ by manufacturer. A service described as “soft washing” should still follow the instructions for the shingles on your home. This is not a reason to climb onto the roof yourself.
What can help reduce recurring growth?
Arrange appropriate branch trimming, non-abrasive debris removal and gutter maintenance. Address upper downspouts that discharge directly onto a lower roof. These measures can reduce damp, debris-filled areas that favor growth. [2]
Ask a roofing professional before adding copper or zinc strips to an existing roof. Installation can disturb shingle seals or introduce exposed fasteners. [2]
What does algae-resistant roofing actually promise?
Some asphalt shingles include granules that release copper to inhibit blue-green algae. Malarkey states that its shingles featuring Scotchgard™ Protector use a blend containing at least 10% 3M™ Copper Granules. That is a manufacturer statement about those products, not a universal specification for every roof. [4]
Malarkey also distinguishes blue-green algae coverage from other biological growth, including moss and lichens. Read the warranty for the exact shingle and roof system being proposed. [4]
Questions to ask before choosing shingles
- What are the manufacturer, product name and algae-protection designation?
- Which written warranty applies to the proposed installation?
- What discoloration is covered, and what is excluded?
- What remedy is offered, and does coverage change over time?
- Are particular accessories, installer qualifications or registration required?
- What maintenance and claim documentation should the homeowner keep?
Keep the applicable manufacturer warranty with your proposal. An algae warranty is not a prediction of the roof’s service life or a promise that every appearance issue will be covered.
Related roofing video
Comparing asphalt roofing shingles for Michigan homes
Community Construction compares standard asphalt shingles and rubberized asphalt (SBS) roofing materials for Michigan homes, including cost and durability considerations.
If you are planning a roof replacement, use this video alongside the algae guidance above to prepare questions about roofing materials, impact-resistant shingles and written warranty coverage.
Community Construction · Published · Watch on YouTube
Questions to use when comparing roofing estimates
- Which exact asphalt shingle or SBS roofing product is included in the proposal?
- What do its product documents say about algae resistance, impact testing and wind performance?
- What is included in the roof replacement cost, and which warranty applies to the complete installation?
For your project, confirm current product ratings, warranty terms and any insurance-discount eligibility with the appropriate manufacturer or insurer. An estimate should identify the specific roofing system being proposed.
Planning roof repair or replacement in Lansing or our other Michigan service areas? Explore our roofing services and material options, or request a roofing estimate.
When should you request a roof assessment?
Ask for an assessment if you are unsure what the staining is, notice moss lifting edges, or have separate concerns such as a leak, missing shingles or storm damage. Discuss those concerns directly instead of assuming that cleaning will resolve them.
Share the roof’s approximate age, any known product information, when you first noticed the problem and photos taken safely from the ground. Ask the contractor to explain what they found and why they recommend maintenance, repair or replacement.
If replacement is appropriate, compare the proposed scope and material options on our roofing services page. A useful proposal should make clear what is included, what remains uncertain and which warranties apply.
A roofing customer’s experience
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