Black Streaks on Your Roof: What Is Eating Your Asphalt Shingles

🔬 If you have noticed dark streaks running down your roof, you are not alone. Many New Brunswick homeowners see these streaks and assume it is dirt, soot, or tree sap. In most cases, it is something else entirely: a type of bacteria called Gloeocapsa magma.

🌱 What is Gloeocapsa magma?

Gloeocapsa magma is a type of cyanobacteria that thrives in humid environments. It spreads through the air and lands on roof surfaces, particularly asphalt shingles that face north or are shaded by trees. In New Brunswick, where humidity is high and many roofs are shaded, it is a common problem.

The bacteria feeds on the limestone filler that manufacturers add to modern asphalt shingles. Limestone makes shingles heavier and helps with production, but it also provides food for this bacteria. As the bacteria grows, it creates the dark streaks you see on the roof.

⚠️ Why it is not just cosmetic

The black streaks may look like a visual problem, but the damage goes deeper. As Gloeocapsa magma feeds on the limestone filler:

• It breaks down the shingle’s structural matrix
• The dark pigment absorbs more heat from the sun, which can raise shingle surface temperature
• Higher temperatures accelerate oxidation of the asphalt binder
• The bacteria creates a surface film that can trap moisture against the shingle
• Trapped moisture creates conditions for moss and lichen to establish

This is biological weathering, and it compounds with the other aging mechanisms the GoNano white paper describes: oxidation, UV damage, granule loss, and freeze-thaw stress. A roof with active biological growth is aging faster than a clean roof.

💧 Moss and lichen: the next stage

Once Gloeocapsa magma establishes a moisture-holding film on the shingles, moss and lichen can follow. These organisms are more visible than the bacteria and cause more obvious damage:

• Moss grows in the gaps between shingles, lifting edges and allowing water underneath
• Lichen attaches directly to the granule surface and can etch small pits into the shingle
• Both organisms expand when wet and contract when dry, putting mechanical stress on the shingle surface
• Both hold moisture against the roof, which accelerates freeze-thaw damage in winter

🧽 Why cleaning alone is not enough

Many homeowners try to solve this with pressure washing or chemical cleaning. This can remove the visible streaks and moss, but it has problems:

• Pressure washing can blast granules off the shingle surface, which is the opposite of what you want
• Chemical cleaning may kill the bacteria but does not address the underlying shingle condition
• The bacteria often returns because the shingle surface has not changed
• Cleaning does not restore flexibility or support the asphalt binder

Cleaning is a maintenance step, not a preservation step. It removes the visible problem but does not address the molecular aging that the bacteria has accelerated.

🛡️ How preservation helps

The GoNano treatment system is designed to penetrate into the asphalt shingle and interact with the binder matrix. The technical data sheet for Shingle Saver notes that the product resists mold, mildew, lichen, and efflorescence. The treatment helps create conditions that are less favorable for biological growth while supporting the shingle’s structural integrity.

This does not mean biological growth will never return. But a preserved roof with intact granules and supported binder is more resistant to biological colonization than an aging, degraded roof.

The proper sequence is:

1. Assess the roof condition
2. Clean the roof if biological growth is present (using low-pressure methods, not pressure washing)
3. Apply preservation treatment if the roof is still a candidate
4. Monitor periodically for new growth

Frequently Asked Questions

Are the black streaks on my roof dangerous?

The streaks themselves are not immediately dangerous, but the bacteria causing them is feeding on your shingles and accelerating deterioration. Over time, this can shorten the roof’s useful life.

Should I pressure wash my roof to remove black streaks?

No. Pressure washing can remove granules from the shingle surface, which removes UV protection and accelerates aging. Low-pressure cleaning or soft washing is safer.

Will roof treatment stop the black streaks from coming back?

The treatment helps create conditions less favorable for biological growth, but no treatment guarantees permanent prevention. Periodic monitoring and maintenance are still recommended.

Video

Watch: Black Streaks on Your Roof: What Is Eating Your Asphalt Shingles

Tap the play button to watch this short roof preservation video.

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