Shingle manufacturers have come a long way in engineering roofs that are mold, moss, allergy resistant. Some offer legitimate warranties stating that their shingles are engineered against such problems in the environment. Once a roof has moss, mold, mildew or algae growing on it, there are many steps a homeowner can take to lessen or in some cases remove this as a problem, the few things that people should know before they go down that road.
One, pressure washing with a high pressure washer, that is, a pressure washer that has a psi above 2,500 or any pressure washer used with a zero nozzle, that is a nozzle that is a stream rather than a spray, will damage the composite shingles regardless of the quality of the composite shingles applied. As an example, if you applied the most expensive composite shingles money could buy today and then you power washed them with a zero nozzle with a small homeowner power washer 5 years from now, you would a) void the warranty of that roof from the manufacturer, b) you will likely cut a hole or cause there to be a hole in that roof in the near future.
This is one of the biggest mistakes that homeowners make is by renting the power washer at a tool rental yard, using it to clean their roof. They’re happy with the results but they have to call us to re-roof in 3 years. They don’t link the two things, but we know that they’re absolutely linked.