Call any asphalt roofing manufacturer and ask them how to clean their shingles. The technical services department will refer you to the Asphalt Roofing Manufacturers Association technical bulletin - Algae discoloration of roof. If you speak to a senior research scientist, you might get a different answer. There are other chemicals that work, but roofing manufacturers are more interested in selling shingles than in removing fungi from them.

A lot of companies claim you don't have to replace your roof because they can clean it. They will tell you they use a safe method, the one recommended by the A.R.M.A. That's what we did our first year roof cleaning when we were inexperienced. The A.R.M.A. recommends using chlorine bleach and trisodium phosphate. Bleach (sodium hypochlorite) is a biocide that is not effective on a porous surface. Trisodium phosphate is a strong cleaning agent but cannot kill biological growths and is a pollutant under The Clean Water Act. The combination of these two will diminish the stains, but will not completely remove the biological growth. The A.R.M.A. actually states that this method is only temporary and that the stains are difficult to remove from roofing surfaces, but may be lightened by applying these chemicals. Some companies will use the technical bulletin as justification for their method. It is to their advantage to clean with a bleach solution. It's inexpensive, faster, and because stains reoccur sooner, it's good for repeat business. Additionally, what these companies won't tell you is how many gallons of this corrosive solution they have to spray in order to diminish the stains.

Our roof cleaning method is a combination of the perfect chemical composition and thorough rinsing system that doesn't just bleach or lighten the stains; it completely removes the biological growth.