The roof cleans we are seeing lately from some of our “competitors” are a jet wash to the roof With no treatment provided. This unfortunately has no longevity to the clean and the moss or biological growth will return with a vengeance in most cases. If you use a professional biocide product with regular applications every 2-3 years the moss will never return. speak to people who are into the service for the long term and not someone you will never see again