Some effective roof cleaning methods include spraying the roof with a mixture of hot water, bleach and detergent along with using lye cleaners or using noncorrosive cleaners. Installing copper or zinc strips near the roof peak can help keep moss and algae from building up, notes ThisOldHouse.com.
One of the more effective methods of cleaning mold, moss and algae from a roof is to wash them away with bleach. To make a homemade cleaning mixture, add hot water, bleach and detergent to a garden sprayer. Do not use a pressure washer, as the high pressure can damage the roof. Take care when using bleach, as it can corrode the metal around the gutters, downspouts and flashings, states FamilyHandyman.com. It is also helpful to spray plants with water beforehand, as bleach can damage plants and the water helps keep the substance from sticking to leaves.
Lye cleaners can also be effective cleaning products because they do not cause as much harm to garden plants as bleach does. However, they can be corrosive to metal.
Noncorrosive roof cleaners are generally good choices, as they do not damage metal and are environmentally friendly. Defy is a safe product to use, recommends FamilyHandyman.com.
Scrubbing can get rid of any stains or growths that spraying leaves behind. Scrub shingles with a broom.
To keep algae and moss from growing back, install a line of copper or zinc along the ridge of the roof. When it rains, the metals run down the roof and kill the algae.