What is Algae Growth?

Definition

Black streaking and discoloration on asphalt shingles caused by Gloeocapsa magma, a cyanobacteria (blue-green algae) that feeds on the limestone filler in shingles. Algae is primarily an aesthetic problem, darkening roofs and making them look older than they are, but sustained algae colonies can accelerate granule loss. Algae-resistant shingles contain copper granules, and zinc strips can be installed at the ridge to prevent or slow growth.