Moss is a fact of life in the Pacific Northwest.  Moss growing on a roof causes shingles to raise allowing wind and rain underneath and will shorten the life span of asphalt roofing materials and untreated wood.  The more the moss grows the more moisture it will hold against the roof slowing it from drying out after it rains; this in turn causes rot.

Moss removal will help maximize the life of your roof as well as enhance the appearance and is often required by your insurance company.

Moss should be killed and then swept from the roof.  After removal of the moss you can hinder the growth by using a granulated environment friendly moss killer and putting it on both sides of the ridge.  Each time it rains some of the granules will wash over the roof making it difficult for moss to grow.