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Moss on Roofs

Written by University of Minnesota Extension faculty

Moss, lichen and algae grow actively in wet weather and can be found on rooftops, decks, lawns, walkways and shady sides of outdoor structures. Results of research in Oregon can be found at Oregon Research which describes types of mosses found in these locations.

Following are suggestions from Oregon State University to control moss, algae and lichens on roofs:

• Scrape away as much moss as possible. A power washer works to remove moss, lichen and algae. Be careful with the tools, as they can damage your roof as well as remove the moss.
• Keep all organic debris such as leaves and branches off of your roof, deck or patio.
• Remove branches that overhang your roof and decks to allow direct sunlight and good aeration to reach your roof.
• Use commercial moss removers to keep moss and algae from returning. These are best applied when the moss is actively growing. If possible, apply them during a dry spell.

Controls containing zinc sulfate are relatively safe around plants and are available for home use. Zinc sulfate also comes in a granular form for dry application. Zinc sprays or granules will corrode copper so should not be used if gutters and downspouts are made of copper. Always read the container's label for directions and make sure it controls the fungi you're trying to eliminate.

Zinc galvanized ridge caps, copper flashing or copper wires on the roof can also be used to help prevent moss and other growth, once moss is removed. Rain leaches down small amounts of the metal, which may help prevent moss, lichen and algae from taking hold. The metal flashing or wire protects from the roof ridge to 10-15 feet down the roof. For larger roofs, wire may be strung at points across the peak of the roof and across the halfway point. This method will help protect the entire surface from growth.

Do not use table salt on your roof. It is corrosive to metal and not very effective at controlling moss. Additional information about chemical control strategies can be found at Oregon State.