Homeowner Use and Maintenance Guidelines
Mildew is a fungus that spreads through the air in microscopic spores. They love moisture and feed on surfaces or dirt. On siding, they look like a layer of dirt. To determine whether you are dealing with mildew or dirt, wipe the surface with a cloth or sponge dampened with bleach. If the bleach causes the surface to lose its dark appearance, you are most likely seeing mildew.
Cleaning mildew from your home is your responsibility. Solutions that remove mildew are available from local paint or home improvement stores. Wear protective eyewear and rubber gloves for this task; the chemicals that remove mildew are unfriendly to humans.