Over time, your siding accumulates dirt just like any surface will. Along with this dirt, there are spores and fungus floating in the air. These spores and fungi like cool and moist locations to grow. The shady sides of your home provide a perfect growing medium for these organic materials. It does not matter if your siding is wood, vinyl, cement board, aluminum, stucco or EIFS (Exterior insulation and finish system). These organics latch on to the siding and with time and moisture, they grow. Organic materials like algae and lichens are unsightly and take away from the curb appeal of your home.