How to Clean Algae Stains off Asphalt Shingle Roofs

Algae stains are often mistaken for mold or dirt on 3-tab asphalt shingles in Atlanta. Although some of these dark streaks on the shingles may be dirt or mildew, algae is a more common explanation, because the spores are airborne and grow easily on the shingles, especially in humid areas. While algae stains don’t harm the shingles themselves, if you want to get rid of the unsightly stains, here are a few tips.

Cleaning

You can clean your roof using either a store bought solution that’s specially made for removing algae stains, or you can use a solution of soap and water. The results will be even better using oxygen bleach. Chlorine bleach has the best results, but you’ll have to be very careful to protect any surrounding vegetation when rinsing the solution off. If your roof is under warranty, carefully read the paperwork to be sure you don’t use anything that would void the warranty, such as a power washer. The easiest way to apply the solution to the roof is with a pump sprayer. Spray the roof in about 4 foot sections starting at the top of the roof, allow the solution to sit for about 15 minutes, and rinse with a hose. You may use a scrub brush if necessary. It’s best to clean the roof on an overcast day so that the cleaning solution doesn’t evaporate as quickly.

Special Shingles

Although cleaning does effectively remove the stains, they will end up returning because of the humidity that Atlanta asphalt shingles are exposed to. So if these stains really bother you and you’re thinking of replacing your roof anyway, you may want to consider special algae resistant shingles. These are basically made by mixing copper granules into roofing products to limit or prevent algae growth. If replacing the roof isn’t an option, you can install a strip of copper just below the ridge of the roof or special zinc strips made for algae prevention.