Roof cleaning is the process of removing algae,[1] mold, mildew, lichen and moss from roofs.[2] Also cleaning oxidation on metal roofs. Cleaning can extend the duration of a roof's ability to function.[2] Algae and other types of build-up often form on the north and west parts of roofs that are shaded or receive less sun, and can reduce a roof's life expectancy.[2] The presence of soot, dirt, or biomass can affect how much sunlight is absorbed by a roof and thus the amount of heat a building absorbs.[3]
Cleaning may be accomplished with a bleach or sodium percarbonate solution,[4] various cleaning products or commercial cleaning services. The Asphalt Roofing Manufacturers Association (ARMA) recommends using a 50/50 solution of household strength sodium hypochlorite (pool chlorine) and water to remove moss and algae.[5] The addition of zinc strips near the roof's peak may reduce the regrowth of algae and moss. Zinc sulfate can also be applied on an annual basis.
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