Algae Staining On Shingled Roof Surfaces

Black Roof Stains: What They Are and How to Handle Them

What Are Those Black Stains on the Roof?

Those black streaks are likely algae — specifically, Gloeocapsa Magma. Algae appear as dark stains on shingles, often more concentrated on the lower roof sections and gradually tapering near the ridge. While algae don’t typically shorten the life of your shingles, they can indicate other roof problems that may be developing.

How Does a Roof Get Algae?

Algae spread through airborne spores. These microscopic spores travel from one contaminated roof to another and thrive when they land on a damp surface. Once established, the algae form a dark UV-resistant coating to protect themselves from sunlight.

How Does It Grow?

Algae require moisture and mild temperatures to grow — conditions frequently met on shaded or north-facing roof surfaces. Dew, rain, and high humidity contribute to their spread. Although most common in the southeastern United States, algae can grow almost anywhere in the country where moisture is present.

What Solutions Do I Have?

1. Install algae-resistant shingles. Products like GAF Timberline HDZ shingles contain copper-infused granules that inhibit algae growth, keeping your roof cleaner for longer.
2. Use a safe roof-cleaning solution. If a new roof isn’t feasible, you can clean algae using a GAF-recommended solution of 4 gallons of water, 1 gallon of bleach, and 1 cup of trisodium phosphate (or a phosphate-free alternative). Apply with a garden sprayer, let sit for 15–20 minutes, and rinse with low-pressure water. Always protect surrounding landscaping and never walk on a wet roof without proper precautions.

What Not to Do

Do not pressure wash your shingles. While some roof cleaning companies offer power washing services, this method is not recommended. It can strip the protective granules off your shingles, causing premature aging and voiding your roof warranty.

Where Can I Get More Information?

If you’re dealing with algae stains or considering new shingles, contact your shingle manufacturer’s technical support for guidance. Most shingles installed by SonShine Roofing are GAF products.

📞 GAF Technical Service: 800-ROOF-411 (800-766-3411)
🌐 Visit the GAF official website for more technical details and product information.

For a long-term solution, explore roof replacement options or join our Roof Care Club for routine maintenance that protects your investment and keeps your roof looking great year-round.