Moss on your roof may look quaint like you’ve stumbled across something out of Hansel & Gretel but it can actually do serious damage to a roof. Left unattended it can cause almost any roofing material to degenerate and drastically shorten its lifespan. Let’s look at the problem and how to solve it.
Moss and Mold
Moss is a plant that grows best in cool, moist, shaded areas. Moss doesn’t produce flowers or seeds, reproducing by spores instead. It also has no root system; rather, it attaches using tiny threads to anchor itself to your roof.
As moss grows on a roof, it lifts shingles and allows for water to penetrate underneath the shingle and cause wood rot and leaks. Also by moss lifting the shingles, it can make your home more susceptible to damage from high wind. In a bad Nor’easter, a mossy roof is more likely to have some shingles stripped off.
True mold is a type of fungus. The mold-like stain most commonly seen on residential roofing isn’t really mold: it’s actually a blue-green algae. Although it looks bad, this “mold” does no damage to roofs. It’s common in warm climates, and not a big problem in Maine, so we’ll focus the rest of this discussion on moss.
Tips to Prevent and Remove Roof Moss
Since moss grows best in the shade, cutting back trees that shade your roof may prevent it from taking hold, kill what’s there, or at least reduce its rate of growth.
You can prevent a moss from occurring or returning by installing zinc or copper. Install 6-inch wide strips of zinc or copper under the row of shingling closest to the roof peak, leaving an inch or two of the lower edge exposed. When it rains, molecules of the metal will wash down the roof. These molecules are toxic to moss and algae. Asphalt shingles are also available with metal particles embedded in the mineral granule surface. If you’re re-roofing and your roof is in a shady location, consider installing algae resistant shingles, these as a reliable preventive.
If there’s already heavy moss growth on your roof, you’ll want to remove it chemically. Some popular brands you can use are Shingle Shield, Spray & Forget, Wet & Forget and Roof Wash. You can also make your own moss remover. In a large spray bottle by using one of these recipes:
- 8 ounces Dawn Ultra dish soap + 2 gallons of water
- 1½ to 3½ cups chlorine bleach + 2 gallons of water
- 1½ to 3½ cups white distilled vinegar + 2 gallons of water
Don’t use a power washer, as this can damage the shingles. Before you begin spraying and of the chemical mixtures, thoroughly wet down the area of the roof with plain water first and around your foundation. This will dilute the chemicals that run off the roof and minimize damage to plantings and discoloration of siding. Apply the cleanser and let it sit for 20 to 45 minutes. Lightly scrub with a soft-bristle brush, then rinse the area with water.