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Discouraging moss growth on a roof
Question:
I've sent along a photo to show you the problem I'm having with my roof. You can see the area beneath the downspout is dark green with a mossy substance. Is this mold? Why is this happening? What can I do to take care of it? If I don't do anything, will it harm the roof in any way?

The installation of the gutter and downspout seem to be OK, but I'd probably have asked the contractor to extend the downspout a few more feet. That way, less water would be running over the shingles. The problem likely is that the green, mossy shingles below the downspout are on a shady portion of the roof, which means they are not drying properly. If you can, trim away any overgrown tree branches, so a little more sunlight reaches the shingles. This will help them dry naturally.

Secondly, consider using zinc or copper strips that clip under the shingles and act as a natural algicide. When water washes over the strips, it picks up tiny metallic particles. Since zinc and copper are natural algicides, they prevent the growth of roof algae, fungus, mold and moss. On Long Island, where the weather features frequent rain and high humidity, it's common to see roofs stained with black or green mold. If left unattended, the mold growth will shorten the life of the shingles.

You also can use any of several commercial roof cleaners, which, like the metal strips, are available at home centers and roofing supply stores. Whether using the strips or a cleaner, you or someone else will have to climb the roof to do the work. You might find a small roofing company to perform such a service, and I'd inquire at a roofing supply store about a list of contractors.

Zinc or copper strips should last several years. If you choose to just use a cleaner, remember you'll have to repeat the process every year or so. Chances are, if there is a buildup of algae, you'd be wise to first treat the shingles with a cleaner and then install the metal strips as a preventive measure. If you have a hard time finding either the strips or a cleaner, visit ZincShield.com (800-440-3010), a South Carolina company that sells several roof maintenance products.
Written By:  Temporary 
Date Posted: 2008-01-09  

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