The unsightly look of moss on roofs is not the only reason that control of this moss is important. Moss will often grow so vigorously that it causes the shingles or shakes to become loosened and raised. Under very wet conditions, water can back up under these raised areas and cause interior leaks and water damage. Often accompanying the moss will be a green coating of algae on those areas that the moss has not yet colonized. Algae become very slippery and treacherous and have been implicated in more than one roof-related disaster. Call a professional to remove your moss problem.