06/20/2026
Gloeocapsa magma is a photosynthetic cyanobacteria (often mistakenly called algae) that causes unsightly black or dark green streaks on asphalt shingle roofs. These airborne spores thrive in warm, humid climates and on shaded, north-facing slopes where moisture lingers.
The bacteria feeds on limestone filler (calcium carbonate) embedded in asphalt shingles for durability and weight. This feeding process weakens the shingle structure and loosens protective surface granules, which then wash into gutters.
Untreated infestations lead to several significant issues:
Premature Roof Aging: The loss of granules and structural degradation shortens the roof’s lifespan, potentially leading to total failure.
Increased Energy Costs: The dark bacterial colonies absorb more solar heat, reducing the roof’s reflective power and increasing indoor cooling loads.
Moisture Retention: The bacteria hold moisture against the shingle surface, creating an environment conducive to further damage from moss, lichen, or rot.
