How to Deal With Blue-Green Algae on Asphalt Shingle Roofs

The ugly black streaks often seen on asphalt shingle roofs are caused by gloeocapsa magma, more commonly known as blue-green algae. So, if it’s on your roof, what do you do about it? Here are some tips.

Blue-Green Algae

Algae is a type of bacteria, but it has plant-like qualities like photosynthesis and the ability to subsist on moisture alone. Blue-green algae is an airborne species that thrives on outdoor surfaces like rooftops. They secrete a dark outer layer that protects them from long-term exposure to ultraviolet (UV) radiation and heat from the sun.

This black substance is what causes the black streaks on the roofing surface. In addition to moisture from rainwater, blue-green algae also “eats” the limestone filler that’s used to make the asphalt shingle granules. While it doesn’t cause substantial damage to the roofing surface, the black streaks can certainly make it ugly.

How to Get Deal With Blue-Green Algae

If your roof already has unsightly black streaks, don’t panic: there is more than one way to deal with it.

• Spray the roof with either a diluted bleach solution or a commercially available cleaning solution that’s specifically formulated for algae removal. If you wish to use a pressure washer, use low-to-medium nozzles. Anything stronger would strip the roof of its outer layer.
• Install zinc strips at the roof ridge. The algae-killing zinc is dispersed onto the roofing surface when it rains. During dry spells, you can use a garden hose to simulate rain on the roofing surface.
• Hire a professional roof cleaning service. Look for services that guarantee algae-free roofing for certain periods.

GAF StainGuard Plus™ Shingles

If your roof is up for replacement, consider asphalt shingles that prevent algae growth. Roofing manufacturer GAF offers StainGuard Plus™ Shingles. These contain algae-fighting copper capsules blended with the roofing granules. Other similar products run out of copper too fast so GAF addressed this problem with their proprietary TIme-Release Technology, which releases copper particles slowly but consistently throughout its service life.

A1 Roofing & Construction Company is your leading provider of roof repair and installation services. Give us a call at (401) 265-1019, or fill out our contact form. We serve customers in Providence and Warwick, RI, as well as in New Bedford, MA.