Power washing a roof to remove growth also dislodges the granules of the shingles, shortening the life of the roof & likely voiding the warranty. Low pressure roof cleaning, or ‘soft washing’, consists of applying a professional detergent to the shingles without using any pressure to effect the treatment. The detergent has a built in surfactant that keeps it in place while it destroys the algae, moss, & lichen growing on the roof without damaging the shingle granules. The biodegradable detergent neutralizes in a short time and rinses down safely in the rain