Before cleaning your asphalt shingles, it is important to contact the shingle manufacturer. They may have specific cleaning directives for caring for your shingles. In addition, be sure to ask if taking any action to clean your shingles will void out the warranty on your roofing. If this is the case, contact a professional to assist you with your roof cleaning needs.
Purchase a roof cleaner from your local home supply store. Check to see that it does not contain bleach or trisodium phosphate (TSP). These are common cleaning agents, but they will only kill surface mold and not penetrate the shingles. They are also harsh on surrounding plants and can cause your shingles to warp and curl. In lieu of bleach and TSP, the cleaner will likely have a high alkaline level and surfactants.
Spray the entire affected area of the roof with the cleaner. If it did not come in a container with a hand pump, transfer the liquid to a container fitted with a spray pump. Allow to penetrate for at least 15 minutes. This gives the chemicals time to kill the surface fungus and seep into the pores of the shingles to remove any additional growth.
Finish the Process
Rinse away the product with a garden hose. If the run-off will reach plants, it is a good idea to spray them down first to make their leaves and roots less vulnerable to the chemicals. Feel the roof to check for presence of fungus. If it is slippery, repeat the process.
Consider installing copper or zinc strips to the surface of the roof to prevent future fungus growth.