My roof has ugly black streaks on it, what is causing it?
Most roof stains are caused by the growth of algae, lichen colonies or moss that feed on organic matter frequently found on roof surfaces. The portions of a roof that receive the least amount of sunlight are more likely to have roof stains. This explains why some homes may have roof stains only on one side of the roof, typically the northern and/or western exposure or in heavily shaded areas.
