What Are the Black Streaks on My Roof?
Ever pulled into your driveway and noticed dark black streaks on your roof? If so, you’re not alone—and you’re probably wondering what they are, and if they mean trouble.
At Restoration Roofing, we hear this question all the time from Collierville homeowners. Black streaks can look alarming, but the good news is they don’t always mean it’s time to panic—or replace your entire roof.
In this blog, we’ll answer:
- What causes black roof streaks
- If they mean your roof needs to be replaced
- How to prevent them
- How to safely remove them
What Causes Black Streaks on a Roof?
Those dark streaks are usually caused by a type of airborne algae called Gloeocapsa magma. It feeds off the limestone filler in asphalt shingles and thrives in warm, humid conditions—just like we have here in Tennessee.
This algae tends to form on parts of your roof that:
- Receive less sunlight
- Retain moisture longer
- Are shaded by overhanging trees
While algae can make your roof look old and dirty, it’s primarily a cosmetic issue. However, if left untreated, it can lead to moss growth, which can cause damage by trapping moisture.
Do Black Streaks Mean I Need a New Roof?
No—not necessarily.
Algae buildup is common as shingles age, but by itself, it doesn’t affect the structural integrity of your roof. However, it does indicate your roof is starting to show signs of wear.
If you also notice moss, mold, curling shingles, or frequent leaks, then it could be time to consider a replacement. But if black streaks are the only issue and the roof is performing well otherwise, cleaning may be all you need.
Still, it’s smart to start budgeting for future replacement if your roof is over 15–20 years old.
How Can I Prevent Algae Streaks from Forming?
Preventing algae isn’t guaranteed, but there are effective ways to slow or stop it:
1. Install Algae-Resistant Shingles
Many modern shingles come with copper or zinc granules baked in, which inhibit algae growth. Atlas, GAF, and other top brands offer long-lasting algae protection with multi-year warranties.
2. Use Zinc or Copper Strips
Installed at your roof ridge, these strips release metal ions when it rains. As water washes over the roof, it distributes algae-killing ions down the surface.
3. Trim Back Trees & Clean Gutters
By letting more sunlight hit your roof and minimizing moisture buildup, you create a less hospitable environment for algae.
These methods work best when combined—and especially on newer roofs where prevention makes the biggest difference.
How Do I Remove Black Streaks From My Roof?
If your roof is still in good shape and you just want it to look better, cleaning is an option. But skip the pressure washer—it will strip granules, damage shingles, and void warranties.
Instead, follow manufacturer-approved cleaning practices:
- Mix 50:50 solution of laundry-strength bleach and water
- Apply with a garden sprayer and let it sit for 15–20 minutes
- Rinse off gently with low-pressure water
If you prefer a non-bleach approach, there are commercial roof-cleaning solutions available.
IMPORTANT: Always consult a professional to avoid damaging your roof or injuring yourself.
So… When Should I Be Concerned?
Algae streaks are mostly an aesthetic nuisance. But if they appear alongside other issues—like:
- Granule loss
- Lifting or curling shingles
- Active leaks or water stains
- Widespread moss or vegetation
…then it’s time to get your roof professionally inspected.
Let Restoration Roofing Evaluate Your Roof
At Restoration Roofing in Collierville, we believe in honest inspections and reliable advice. We’ll assess whether your roof simply needs a safe cleaning—or if it’s showing signs of age that require replacement.
Our team offers:
- Free inspections
- Algae-resistant shingle upgrades
- Soft-wash cleaning
- Full roof replacements backed by warranty
Call us today to schedule your inspection and let us restore the beauty and performance of your roof—streak-free and stress-free.
Contact us today to schedule your inspection and get a no-pressure quote from Collierville’s trusted roofing experts.
Choose Restoration Roofing and get the protection your home deserves. Give us a call at 901-854-3402 or fill out our Contact Us form and we will reach out to you with our next available inspection. Make sure to follow us on Facebook and Instagram for more tips on finding the best roofing contractor for you.
