What cleans roof shingles?

What cleans roof shingles effectively while remaining safe for asphalt depends on whether you are dealing with black algae streaks, moss, lichen, or general dirt. For black algae streaks caused by Gloeocapsa magma, the industry standard recommended by shingle manufacturers like GAF and Owens Corning is a solution of oxygen bleach, not chlorine bleach. A mixture of sodium percarbonate or a 50/50 mix of water and oxygen bleach applied with a low-pressure garden sprayer, allowed to dwell for 15 to 20 minutes, and then gently rinsed with low-pressure water from the ridge down, is effective. Many homeowners use commercial products like Spray and Forget, Wet and Forget, or Roof Shampoo that are specifically formulated to be shingle-safe and require no pressure washing. For moss, products containing potassium salts of fatty acids, zinc sulfate, or zinc strips are effective, as moss needs to be killed first and then gently removed after it dies. Never use pressure washers, as high pressure strips protective granules and voids warranties. Never use undiluted chlorine bleach, as it can corrode metal flashing, kill landscaping, and damage shingles. Always protect plants by wetting them before and after cleaning, work on a cool overcast day, and spray from ridge downward to avoid driving water under shingles. For severe moss or widespread growth, professional roof cleaning is safest.