By Paul Bianchina
Q: I installed a new three-tab roof about nine years ago, and put a 5-inch strip of zinc under the ridge to prevent roof moss. However, I still have streaks of moss, even in areas that receive sun. Interestingly, the area under the aluminum skylight is free of moss, so I bought some aluminum flashing material. Will that work? What about copper? Any other suggestions?- Walt S., via e-mail.
A: Moss, which doesn't actually have a deep root system like other types of plants, needs a relatively constant flow of moisture in order to survive, and typically does not do well in warm, sunlit areas of the roof. So, there are several things you want to be sure to take care of first:
Cut back overhanging tree limbs and remove buildups of leaves and pine needles to allow as much sunlight as possible to reach the roof.
Increase the flow of ventilation in the attic. This helps minimize moisture buildup right below the shingles, which can help with moss buildup.
Clean the roof on a regular basis - once or twice a year - to remove the moss. The more you can minimize its colonization on the roof, the less of a problem you will have with buildups. Since the roots are so shallow, cleaning can be done quite easily and effectively with a long-handle scrub brush or with a spray from a garden hose, but it must be done from the top down, not the bottom up, in order to minimize potential damage to the shingles. Be very careful with any rooftop cleaning to avoid potential injury to yourself!
Zinc strips have been used with mixed success in the prevention of roof moss. The strips should be nailed at the ridge, and as rain flows across the strips it washes small amounts of zinc carbonate over the shingles, which controls the moss to some degree. Many larger roofing retailers can order the right type of zinc strips for you if you want to try them again.
Copper strips will do the same thing, and copper is actually considered by many to be superior to zinc because it provides longer lasting protection. The copper strips are installed at the ridge, where they will eventually oxidize to form the familiar green color. Here again, rain washing across the copper will release small amounts of copper sulfate and carry it down the roof, killing the moss. Copper strips can be ordered from many roofing products suppliers, or you can visit any sheet metal shop and have copper cut to order for you. Install it under the ridge shingles with about four inches exposed to the weather.
Aluminum shouldn't have any effect on moss. I suspect that either the sunlight reflecting off the aluminum is keeping the moss at bay in this area, or possibly heat being lost through the skylight is keeping the shingles warmer and drier.
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