Cleaning moss off of your roof not only improves the appearance, but also increases the life span of your roof. Moss will often grow so vigorously that it causes the shingles or shakes to become loosened and raised. Water can back up under the raised areas and cause leaks and water damage. Along with the moss will be green algae that can become very slippery, and have been implicated in more than one roof-related disaster.
Moss growth tends to occur on the north slopes of roofs and on areas with overhanging trees. To help gain control over moss, trim trees that shade your roof, and remove organic debris such as conifer needles, branches, leaves etc.
It may be possible to hose off or sweep plant debris from the roof. High-pressure hose equipment is very effective in removing moss and debris. Other methods of removal and control are zinc strips, Metal flashing, Zinc Sulfate, Zinc Chloride, or chemical and bleach products made especially for moss.
No matter what you decide to do, if your roof is steeply sloped, don’t get up on it- hire a professional to tackle the job.