black streaks on roof Georgia

Black streaks on asphalt shingles are algae

The dark runs, especially on the north slope and under trees, are almost always Gloeocapsa algae. Pressure knocks off granules. Granules are the roof.

Those black streaks are a colony, not dirt that blew on. Asphalt shingles stay damp just long enough, in this climate, for algae to run downhill with the rain. A roof soft wash is a treatment that kills the colony and lets it release. It is applied so we are not scouring the shingle. The granules that shed in a gutter after a pressure wash were the roof’s sunblock. They do not grow back.

The roof often looks uneven the same day and more consistent after weather finishes the release. If someone promises “white shingles before lunch” with a surface cleaner, they are promising a shorter roof. We will also say no when the shingles are already curling, cracked, or bald. A pretty treatment on a failed roof is a wasted fee.

Metal roofs, tile, and slate are not this article and not this price. They are quoted after we see the finish. We do not treat every roof as asphalt because the truck is already there.

The service this belongs to is Roof soft washing.