Celebrating seven years without injury!
A1 Pressure Washing's low pressure roof cleaning. Low pressure means that the soap and detergents are gently sprayed on, given time to work, and then gently rinsed off. Unlike normal pressure washing, there is no force involved, therefore, no damage to the shingles.
The black streaks on a roof are usually just mostly mold (thick mold, but still just mold). The mold starts in sporadic places and then, rain and gravity pull the colonies' growth downward, forming streaks. Often misinterpreted as needing a new roof, solid black roofs are usually just streaks of mold that have grown together into a super colony.