According to the Asphalt Roofing Manufacturing Association, in order to maintain your roof warranty you are required to keep your roof clean of bacteria, algae, moss, mildew, and other growths on the roof.  According to Tom Bollnow of the Asphalt Roofing Manufacturers Association (ARMA), “The algae is mostly an aesthetic nuisance, although with time, the moisture retained in the algae can prematurely age the shingles.”  The algae roots wrap around the roof particles, and as the algae thickens and spreads laterally, it pushes and expands, removing particles in the process.   This staining is not just a cosmetic stain it is a harmful algae called gloeocapsa magma and it is degrading the roof shingle.  Photosynthesizing Cyanobacteria, is the most successful microorganisms on earth. Yes, you have bacterial colonies living and feeding off your roof. Besides the damage they do by eating the calcium carbonate, limestone layer, they also promote the colonization and growth of other destructive organisms. When they eat the limestone filler in the shingle, they fix nitrogen into ammonia which acts as a fertilizer source for moss, algae and lichens to grow and flourish. If this algae and bacteria is not killed it will shorten the life span of the roof and it will need to be replaced earlier than expected. 

Power washing can damage your roof and void your roof warranty. 
That is why it is recommended to use soft washing to maintain the roof.  For a fraction of the cost of replacing your roof, you can service it and keep the warranty up to date and add years of life to the roof.

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