What Do Black Streaks on a Roof Mean, and Should They Be Cleaned Before Winter?
Black streaks on an asphalt shingle roof are usually caused by algae, often Gloeocapsa magma, rather than ordinary dirt. For South Shore and Cape Cod homeowners, fall is a practical time to have the roof evaluated and, when appropriate, professionally cleaned before winter weather arrives. The safest approach is low-pressure roof cleaning, not pressure washing….
