What causes black streaks on asphalt roof shingles?
Unsightly black stains on shingles are often mistaken for fungus, mildew, dirt or oil, but are actually caused by a hardy type of algae. This common problem has increased during the past 20 years, indiscriminately settling on rooftops from coast to coast. Dark algae streaks are visible when algae cover the normally vibrant colors of white, cobalt blue or hunter green roofing granules.
