In the Pacific northwest it's very common to have moss, algae and lichen growth on our roofs. These fungi are not only unsightly but they can do damage to our roofs integrity over time if not removed and treated. We use the most effective and gentle method for moss removal which is to hand clean the moss using a brush. I've heard from too many home inspectors that pressure washing a roof is very hard on the shingles and many an inspector has had to make a note of this damage in their inspections. So for your home's well being in principal we approach this issue with a scalpel rather than a Chainsaw! We also treat the roof after cleaning with an environmentally safe product (zinc sulfate) to prevent the re- rooting moss.