What You Need to Know About the Blue-Green Algae

If you see black or dark brown streaks on your roof, you might assume that these are mold, mildew, or moss. However, more often than not, these dark stains are due to a tiny bacteria called Gloeocapsa magma or blue-green algae.

According to roofing companies, this bacteria thrives in moist environments and travels through wind. That said, if you notice blue-green algae on your neighbor’s roof, there’s a chance that your own roof has been exposed to it as well.

Unfortunately, blue-green algae can impact the appearance and resale value of your home. But more than that, it can also negatively affect the long-term performance of your roof. In this post, Oberg Roofing & Remodeling shares some tips on how you can treat and prevent this roofing issue.


You can rely on commercially available cleaning solutions to remove the stains on your roof and impede the growth of algae for a year or two. Experts recommend applying a 50/50 solution of chlorine bleach and water to your roof. Make sure to rinse off after 15-20 minutes. It’s also best to leave this job to professionals so that you can get a proper assessment of your roofing and determine whether you need a roof replacement or not.


It’s a common solution for homeowners to add copper and zinc strips at the roof ridge. This part of the roofing is typically where rainwater can pick up the algae-preventing metal ions and distribute them on the roof. But obviously, since it depends on rain to be able to do this, this might not be the most effective method. That said, you might want to consider opting for the StreakGuard™ Algae Resistance Protection from Owens Corning®. It makes use of copper-lined granules that help resist algae growth. With a limited 10-year warranty, it can definitely give you peace of mind that your roof will be protected against blue-green algae.

Oberg Roofing & Remodeling is a trusted company that specializes in steel roofs and a variety of roofing services. We carry out projects to a high standard, so you can expect quality results from our crew. Call us at (320) 204-2264 or fill out our contact form to request a free estimate. We serve customers in St. Cloud, MN.

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