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.