Moss that grows on the roof of your house does not damage the shingles outright, but moss does trap water on the roof, providing a welcoming environment for molds and fungi. Moss must be either removed or killed to avoid eventual damage from these organisms. Moss is indiscriminate and grows on any type of roof -- asphalt shingles, wood, clay tiles or metal. Removing moss completely involves climbing to the roof and physically pulling it off the shingles, which can be dangerous, but killing it is as easy as spraying bleach.
Mix one part bleach to one part water in a 5-gallon bucket. Stir the mixture with a stir stick. Create 1 gallon of this bleach solution for every 50 square feet of roof surface.
Place the backpack sprayer on the ground. Open the valve to the holding tank and pour in the bleach solution. Put on the sprayer and turn the device on.
Hold the backpack sprayer nozzle and aim it at the roof. Coat the roof with a thin, even layer of the solution. Repeat the application in one week if any live moss remains.