Most commercial roof tops are either flat or have little to no pitch. Since pitch is the measure of rise from the top of the roof running outward to the edge of the roof, the higher the pitch, the faster water can drain off the roof. Flat roofs, then, will tend to hold water well after a rainstorm has passed. Even with proper drainage pathways built-in, commercial roofs will sometimes have pools of water which will sit long enough to attract mold, mildew, and small debris.
Because of the tendency for flat commercial roofs to get stained or grow mold and mildew, it is necessary and advisable to have your commercial roof cleaned periodically. An annual inspection can help, by keeping a trained eye on the condition of your commercial roof.
Cleaning methods will vary slightly from roof to roof, depending on if you have a roof coating or a built-up tar roof. Because there are many types of commercial roofs out there, so also are their varied methods of cleaning the rooftops. Because of this, it is important to have a professional commercial roofing company oversee the cleaning of your roof.