What Are the Black Streaks on My Roof?
If you've noticed dark, dripping streaks running down your roof, you're not looking at dirt or "wear." You're looking at a living organism, and it's slowly damaging your shingles.
Meet gloeocapsa magma
The streaks are a blue-green algae called gloeocapsa magma. It feeds on the limestone filler manufacturers add to asphalt shingles, and it loves humid climates like the Piedmont Triad. As colonies grow, they form the dark protective coating you see streaking down the roof.
Why it matters
- It shortens roof life. The algae eats the shingle's protective granules, leaving them brittle.
- It raises cooling costs. Dark streaks absorb heat, making your attic and home hotter.
- It spreads. Spores travel on the wind, which is why entire neighborhoods streak around the same time.
- It kills curb appeal. Few things age a home faster than a streaked roof.
Why you should never pressure wash a roof
It's tempting to blast it off, but high pressure strips the granules and can void your shingle warranty. The Asphalt Roofing Manufacturers Association recommends low-pressure cleaning only.
The right fix: soft washing
A professional roof soft wash applies a detergent that kills the algae and moss, then rinses gently. The streaks lift away, the growth is killed at the root, and your shingles are left intact. Results last for years, especially when you stay ahead of regrowth.