Some chemical is used to clean roofs. It can vary depending on what the roof is made of. For example, if it's a black tiled roof, then a mild bleach solution can be used. If it's a coloured concrete roof, then a weak acid such as vinegar can be used. As with any cleaning product, always take care when using and read the manufacturer's instructions carefully.

Alkaline cleaners like TSP (trisodium phosphate) are often used to clean roofs. Be sure to wear a respirator and goggles when using any kind of cleaner, as they can be dangerous if inhaled or splashed in the eyes.