Blue-green algae and how you can help protect your customers from it


The dark stains you see on roofs all over the U.S. and Canada are often caused by tiny cyanobacteria called Gloeocapsa magma — commonly known as blue-green algae.

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It’s a bacteria that travels on the wind and thrives in moist environments — so if one house in a neighborhood has it, others have probably been exposed as well. The darkening effect can impact the appearance and resale value of a home, as well as the effectiveness of highly reflective cool roofs.

Across the U.S., blue-green algae growth is often just a matter of time. The GAF Time- Release Algae-Fighting Technology used on shingles with a StainGuard PlusAlgae Protection Limited Warranty1 is formulated to put time back on your side.

The GAF StainGuard PlusAlgae Protection Limited Warranty1 provides 25 years of coverage against blue-green algae discoloration. It now comes with many of the most popular GAF Shingles, as well as hip and ridge cap shingles and visible starter strips.

Algae protection is important to customers. In fact, when GAF asked homeowners about it, 87% said it was very-to-extremely important to protect their roof from blue- green algae stains.2 89% said warranty length was very or extremely important when purchasing an algae protection product.2

GAF helps answer these customer needs. Shingles and roof accessories with a StainGuard PlusAlgae Protection Limited Warranty are covered for 25 years against blue-green algae discoloration.1 They also provide long-lasting algae-fighting power thanks to GAF Time-Release Algae-Fighting Technology.

Proprietary GAF Time-Release Algae-Fighting Technology

At certain concentrations, metals like copper and zinc are toxic to blue-green algae, and can help prevent it from growing. In fact, on much older homes you may still see pitted copper and zinc strips tucked up under the ridge caps.

Using copper is also the idea behind traditional algae-prevention granules. They contain a layer of copper that leaches onto the roof. And that works for a while. But eventually, the granules degrade and release less copper, which makes them less effective at stopping algae growth.

GAF Time-Release Algae-Fighting Technology delivers the algae-fighting copper in a whole new way. Instead of a copper layer, specially engineered capsules are infused throughout with thousands of copper microsites, which release copper steadily over time, for long-lasting algae-fighting power. It’s algae resistance so powerful it allows us to offer the 25-year StainGuard PlusAlgae Protection Limited Warranty1 on many of our most popular products.

The long-lasting algae-fighting power and warranty coverage your customers want is now available from eave to ridge — only with GAF Time-Release Algae Fighting Technology and the 25-year StainGuard PlusAlgae Protection Limited Warranty.1


1 25-year StainGuard Plus Algae Protection Limited Warranty against blue-green algae discoloration is available only on products sold in packages bearing the StainGuard Plus logo. See GAF Shingle & Accessory Limited Warranty for complete coverage, restrictions and qualifying products.

2 Based on 2021 survey commissioned by GAF of 500 homeowners in areas with moderate to high amounts of blue-green algae.

3 15-year WindProven limited wind warranty on Timberline HDZ® Shingles requires the use of GAF starter strips, roof deck protection, ridge cap shingles, and leak barrier or attic ventilation. See GAF Roofing System Limited Warranty for complete coverage and restrictions. Visit for qualifying GAF products. For installations not eligible for the WindProven limited wind warranty, see GAF Shingle & Accessory Limited Warranty for complete coverage and restrictions.

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