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Battling Roof Moss

Scott Gibson, Contributing Editor

I have a cedar shake roof that's starting to collect moss. My sister says that running a copper wire on the peak would get the moss off and keep it off. My husband is a little skeptical. Is there any truth to this solution?

Be skeptical no longer. I have no way of knowing what your sister's track record might be on home repair and maintenance, but in this situation she's right.

Copper or zinc strips attached to the ridge of the roof will indeed help to eliminate moss. Zinc strips release small amounts of zinc carbonate when it rains. In these modest doses, it shouldn't pose any environmental risks. Copper sulfate is an effective herbicide and fungicide.

Nailing strips of these metals to the ridge to prevent the growth of moss is actually recommended by the Cedar Shake and Shingle Bureau.

Whether you'd get the same kind of protection from a copper wire, which has less surface area than a strip of metal, is something you might have to discover through experience. But it's probably worth a try, and if the wire proves ineffective you can always replace it with strips of metal.

That is, if you don't mind climbing up on the roof a second time.

While the zinc or copper should be effective in keeping moss from prospering, it probably won't be enough to get rid of what you already have. For that you may have to clean the roof. More on that shortly.

Roofs need regular attention

Moss grows on a roof when conditions are right, and that means a damp environment. If there are a lot of tree branches hanging over the roof, removing them is a good preventive measure.

Cedar makes a very long-lasting roof, providing it's been installed correctly and you've used a good grade of Cedar. But Cedar roofs need to breathe to survive. Leaves and other debris should be removed once or twice a year. Make sure that the gaps between shingles are cleaned out so water isn't trapped there.

Adequate ventilation in the attic is also important. Back in the old days, carpenters left gaps between the boards used as sheathing. That practice helped promote good air circulation and dried out the underside of the shingles.

That's generally not done these days because plywood or oriented strand board is typically used for sheathing. But it does point to the importance of making sure that ridge, soffit and gable-end vents are kept clear so they can do their job.

Clean gently, but clean

In my book, few sights are as frightening as a power washer in the hands of an over-ambitious weekend odd-jobber. These devices are useful, yes, but in inexperienced hands the tremendous pressure they generate can strip off paint and damage wood.

If you hire someone with a power washer to tackle your roof, make sure they know what they're doing. You might get equally satisfactory results with a garden hose and a broom.

Be careful if you go up on the roof yourself. If the pitch is more than 4 inches in 12 consider calling a professional. Just ask to see references, make sure you know exactly what chemicals, if any, will be used, and get a written guarantee.

Have a question? Write to me at scottgibson@securespeed.us.

About the Author
An accomplished woodworker and carpenter, Scott Gibson is the former editor of Fine Woodworking magazine, and a former editor at Today's Homeowner and Fine Homebuilding magazines. He also is former managing editor of the Kennebec Journal, a daily newspaper in Maine.

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