What Are Those Black Streaks on Your Roof?
If you've noticed dark streaks running down your roof, you're not alone. It's one of the most common issues we see on homes in Rock Hill and the surrounding area — and it's not just cosmetic.
Meet Gloeocapsa Magma
Those black streaks are caused by a type of blue-green algae called Gloeocapsa magma. It feeds on the limestone filler in asphalt shingles — literally eating your roof. The dark color is a protective coating the algae produces to shield itself from UV rays.
Why It's More Than Cosmetic
- •Shortened roof life: Algae degrades shingle granules, reducing their protective ability
- •Higher energy bills: Dark algae absorbs more heat, making your attic hotter
- •Spreads fast: Algae spores travel through the air and spread to neighboring roofs
- •Reduced home value: A streaky roof makes your entire home look older
How Soft Washing Fixes It
The only safe way to clean a roof is soft washing. We apply a low-pressure solution of sodium hypochlorite and surfactant that kills the algae at the root. No high pressure, no walking on your shingles, no damage. This is the method recommended by shingle manufacturers like GAF and CertainTeed.
Results are dramatic and immediate. Some residual algae continues to wash away with rain over the following weeks, making it look even better.
How Often Should You Clean Your Roof?
Every 2–3 years in the Rock Hill area. Roofs with heavy shade or north-facing slopes may need it more often. A single soft wash can extend your roof's life by 5–10 years.