How to Clean Moss Off Roof Shingles

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Sometimes a homeowner may notice unsightly black streaks or moss on their roof. Many think that the black streaks are dirt and forget about it. However, it could be that the black streaks are caused by a type of algae known as gloeocapsa magma. This is referred to as blue-green or black algae. Moss is easy for most people to recognize and thrives in moist environments, as does algae.
About Gloeocapsa Magma and Moss

Gloeocapsa magma develops a hard coating that is dark in color, creating black streaks. The algae feed on the limestone that is part of the shingles. Over time, the black streaks will worsen and can trap moisture and age the shingles prematurely.
To prevent future algae growth, it may be necessary to install copper or zinc strips along the topmost shingles. When the roof is rained on, the water reacts to the strips, causing a solution to run down the shingles. This solution keeps more algae from forming. However, this will not remove existing algae. In order to do so, it is necessary to clean the shingles. Cleaning is also necessary to keep algae and moss from spreading to other roofs in the neighborhood, as wind and even animals can spread the spores to adjacent homes.

How to Clean Moss Off Roof Shingles

It is recommended that homeowners hire someone to professionally clean their shingles for optimal results. In some cases, it is possible for the homeowner to perform the cleaning themselves. Sometimes a homeowner’s first reaction is to pressure wash the roof. However, even when done by a professional, this may not be effective. It is also dangerous to stand on a wet rooftop and pressure wash. In addition, pressure washing may damage shingles, and the process may not remove the microscopic algae and moss, only the visible layer.

Pressure or power washing may also void the warranty on the roof.

A process known as soft washing is the best way to clean shingles. This method removes not only moss, but algae, bird droppings, and lichen. Soft washing utilizes a cleaning solution, often bleach and water) and sometimes a detergent. Soft washing uses different equipment than power washing. Gutters will need to be cleaned out before the procedure begins. A soft-bristle scrub brush may need to be used to remove moss, but this must be done gently to avoid damaging the shingles.

Homeowners who elect to perform the soft washing themselves should use proper safety equipment, such as a harness and tie-off rope, and another person should be present in case of falls. If the cleaning solution lands on any of the surrounding plants and landscaping, it is necessary to spray the foliage down with clean water. Those present during the procedure should also wear protective gear, such as safety goggles and gloves to avoid contact with chemicals.


Prevention is much easier than cleaning the shingles. Either when the roof is new or after a soft wash, measures should be taken to prevent future gloeocapsa magma and moss growth. Along with the previously mentioned zinc or copper strips, homeowners should not allow debris like pine needles or leaves to accumulate on the roof or in the gutters, especially in warm, humid climates. A leaf blower can be used to remove debris, but airflow should be directed downward to avoid forcing debris underneath the shingles.

Trees around the roof should be kept trimmed. This allows sunlight to reach the roof and helps eliminate debris buildup. There are shingles that can be purchased that inhibit the growth of moss and algae. This type of shingle is recommended in warm, moist climates.

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