Rosie's Roofing and Restoration Atlanta


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For many homeowners in the South, black streaking on the surface of their home’s roof is a common problem. Many people are unaware of the cause of those unsightly streaks, and some will either fail to take the proper steps to address the problem or cause damage to the surface of their roof by trying a DIY approach. The following information is provided by the team at Rosie’s Roofing and Restoration to help homeowners know what to do if they notice black streaks or staining on the surface of their home’s roof.

What is the Cause of Dark Streaking?

In the vast majority of cases, black streaking or staining on a roof is caused by the presence of the algae known as Gloecapsa Magma. The algae is spread when the wind carries spores from one location to another. In order to thrive, the algae needs both food and moisture. The calcium carbonate particles that are used to create most roofing shingles provide an excellent food source for this algae, and the requisite moisture is supplied by rain and morning dew. Once the algae takes hold, it can quickly grow and spread, leaving those hallmark black streaks across the surface of your roof.


What Can be Done About Algae Streaking?

Proper cleaning methods must be employed to take control of algae growth on the surface of a roof. While it may be tempting to take a pressure washer to the streaks, that approach is likely to cause damage to the shingles and reduce their useful lifespan. The best way to get rid of roof algae is by a careful application of a product that is specifically formulated to kill algae. An alternative is a solution of bleach, water and TSP (trisodium phosphate). Spray the solution on the shingles and leave it on to soak. After 15 minutes, make sure to spray the area down with a garden hose.

How to Prevent Algae From Returning

Once the algae has been removed, it is important to take steps to prevent regrowth. You may have noticed that the algae did not grow on the shingles beneath areas of metal flashing, vents or skylights. That is because the presence of metal inhibits the growth of algae. Every time it rains, traces of metal wash down the roof from areas where vents, flashing or other metal elements are installed. Once your roof has been cleared of existing algae, an option for preventing regrowth is to install strips made from copper or zinc along the edge of shingles at the ridge of your roof. As rainwater trickles across those strips and down the roof, an inhospitable environment will be created.

Have a leak in your roof? We can fix it! Contact us

At Rosie’s Roofing and Restoration, a reliable roofing company is always here to help with any questions or concerns that you may have about your home’s roof. When it comes to black stains or streaks, our team can address the matter in a swift and professional manner and advise you on whether the best option is to clean or replace your roof, depending on its age and condition. Call us today to learn more, or to schedule an estimate.


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