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Question and Answer ArticleMossy Roof

By Jennifer T. Derrick
Published: September 1, 2009

Q: At our cabin in the northern tier of the U.S., our peaked roof has moss growing on the north-facing half but none on the south-facing half. Is there a solution we can mix to kill the moss? And I’ve heard there are preventative plates I can slip under the next to last row of shingles that will prevent future growth; do those work? Thanks for your fun publication. Bill Lannom; via e-mail

A: There are many products out there: preventative solutions, cleaning solutions, as well as copper and other metal strips to place on your roof to help deter moss buildup. Zinc and copper strips, when applied to a shingle roof, work to prevent moss growth by way of the metal/chemical runoff that occurs when it rains. There are mixed opinions about how effective such strips are, though. Some claim that they have no moss from the peak of their roof to the gutter. Others say the plates don’t work effectively, giving the roof a streaked or patchy look.

Solutions that kill or resist moss and algae build-up will likely work for a while (one such mixture is a 50/50 mix of chlorine bleach and water). You may, however, want to use non-toxic oxygen bleach instead of chlorine, as it’s better all around for your roof and surrounding environment. Washing your roof using an environmentally safe soap and garden hose can also help clear off algae and moss (the hose is preferred over power-washing, which can be hard on asphalt shingles – especially older ones). But these aren’t permanent solutions; where there was moss before, moss will grow again. Even the most dedicated homeowners can’t stop moss spores from traveling and landing on their roof.

What’s a frustrated homeowner to do? Your best bet, if you have a relatively new roof, is to: (1) carefully clean the existing moss away (push the scrub brush down the roof, not up, so as not to damage the shingles); (2) cut down any overhanging branches from your roof area so that more wind and sun can dry and air out the roof, and (3) make sure to keep dirt and debris from building up on your roof.

If you need to replace your roof soon, you might consider getting a metal roof; they’re easy to clean and will resist moss and algae far more effectively than asphalt or wood shingles. Or you might consider looking at a line of special asphalt shingles that contain high concentrations of zinc- or copper oxide-coated granules for algae and moss relief.  

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