By the time August arrives in the Raleigh-Durham area, the North Carolina summer heat is accompanied by an absolute wall of humidity. While we feel it the second we step outside, your roof feels it 24/7.
This sustained, thick moisture creates a perfect incubator for a very specific, frustrating problem: roof algae, mold, and moss. If you’ve ever looked up at your roof and noticed unsightly black streaks or dark patches, you aren’t looking at dirt or soot. You’re looking at a living organism that is actively feeding on your shingles.
Here is what you need to know about late-summer roof growth, the damage it causes, and how to safely handle it.
1. What Are Those Black Streaks? (Meet Gloeocapsa Magma)
The most common culprit behind dark stains on North Carolina roofs is a blue-green algae called Gloeocapsa magma. Airborne spores travel on the wind and settle on your roof. Once there, they thrive in the hot, humid late summer climate, particularly on the north-facing or shaded sections of your roof that take longer to dry out after a morning dew or afternoon rain.
Why do they love your roof so much? Modern asphalt shingles contain limestone filler to add weight and durability. To this specific algae, that limestone is a delicious, all-you-can-eat buffet. As the algae feeds and multiplies, it leaves behind those familiar, ugly black streaks.
2. Cosmetic Eyesore vs. Structural Threat
While algae streaks are mostly a cosmetic issue early on, they can quickly escalate if left untreated. The dark stains absorb more sunlight, which dramatically increases your roof’s surface temperature and causes your attic humidity to climb even higher.
Furthermore, if the algae is ignored, it ages shingles more rapidly because the algae will extract essential oils that are manufactured into the shingles that provide life-sustaining elements. The progressive algae-induced aging causes shingle edges to dry out, curl, become less effective, and lead to premature roof failure.
3. The Dangerous Mistake: DIY Pressure Washing
When homeowners notice these black streaks, their first instinct is often to grab a pressure washer from the garage or hire a cheap handyman to blast the stains away.
This is a major, expensive mistake.
Asphalt shingles are covered in protective ceramic granules that act as a shield against UV rays and shedding water. High-pressure water will instantly blast those granules right off your roof, severely weakening the shingles and drastically shortening the lifespan of your roof. Even worse, using a high-pressure washer on your roof will likely void your manufacturer’s and/or labor warranty.
The Right Way to Clean and Protect Your Roof
To safely eliminate algae and mold without harming your roof, professionals use a method called soft washing. This process utilizes low-pressure water combined with specialized, eco-friendly cleaning solutions that gently kill the algae at its root, allowing it to wash away safely without lifting or damaging the shingles.
At Jackson Roofing & Gutters, we understand the delicate balance required to keep your roof looking beautiful while fully preserving its structural integrity and warranty.
Want to rid your roof of those stubborn late-summer stains safely? Reach out to Jackson Roofing & Gutters today to learn about our professional roof maintenance and cleaning services!