Defend your roof against moss

​You rely on your roof to protect you from the elements. But this time of year, your roof needs defending against a seemingly harmless foe: moss.

Beautiful in the forest, moss on your roof is another story. It shortens a roof's lifespan because its fuzzy growth and shallow root system trap moisture, promoting rot in cedar shakes, lifting the edges of shingles and shakes and encouraging asphalt shingles to shed granules faster. The more moss, the longer it takes your roof to dry out after a rain or even morning dew. The problem is worse on north-facing portions of the roof, since they receive less sunlight.

Now's the time to show moss who's boss – but attack with caution. Some tools in your moss-busting arsenal can leave your roof in worse shape than when you started. To win the war on moss:

• Trim nearby tree branches to prevent them from shading the roof (creating a moss-friendly environment) and dropping leaves and needles.
• Try dislodging the moss with a stiff broom. This works best if moss isn't extensive and you've had a recent stretch of dry weather.
• If you choose to pressure wash make sure you or your contractor use the gentlest setting that will work. Pressure suitable for cleaning concrete, for example, can shred wood fibers, shortening the life of your roof.
• If your roof is cedar, apply a water repellant formulated especially for cedar roofs after pressure washing.
• Consider an anti-moss treatment (including organic options) specially formulated for roofs. Follow manufacturer's instructions carefully and consider environmental concerns about surrounding vegetation and water.
• Avoid home remedies like sprinkling laundry detergent on your roof. Degreasing agents in the soap can attack and degrade some roofing materials, breaking down their water-shedding properties and causing leaks, sometimes within days of application.
• Avoid walking on fragile roofs. Steer clear of cupped or curled shakes or shingles, which are prone to cracking, especially in cold weather. Clay tile and slate roofs call for extra caution, too.
• And most important: Before you climb the ladder, remember that your roof is a dangerous place, particularly if it has a steep pitch. If you're unsure about your ability to safely de-moss your roof, call a reputable roof maintenance company to handle the job.