Copper Flashing to Prevent Moss on the Roof

Updated February 21, 2017

Moss thrives in damp, cool areas, and cedar shake roofs receive more moss damage than asphalt or metal roofs. Copper flashing offers a low-maintenance way to alleviate mossy roofs, but it's not without complications.

How it Works

As rain falls on copper flashing, the raindrops carry down small amounts of metal, spreading it across the shingles. These small amounts of metal stop moss and algae from growing.


Installing metal flashing around the roof ridge will create a moss-free zone 10 to 15 feet down your roof. To protect areas below that distance, string a thin line of copper wire halfway down the root. This will protect the rest of the roof without detracting from your roof's appearance.


Washington Toxics Coalition suggests using zinc flashing and zinc strips instead of copper, since copper can be toxic to aquatic life. While zinc is "potentially toxic" to marine life, copper flashing is 10 to 25 per cent more dangerous to fish and other creatures, they warn.

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