Roof cleaning is the process to remove algae, mold, mildew, lichen and moss from roofs. Roof cleaning can extend the duration of a roof’s ability to function. Algae and other types of build-up often form on the north and west parts of the roofs that are shaded or receive less sun, and can reduce a roof’s life expectancy. 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. Below is an explanation of the different algae and bacteria.