A common pet peeve among homeowners with asphalt shingle roofs are the unsightly black streaks that appear as their roof ages. But what causes those black streaks and what can be done about them? The source of the streaking is a cyanobacteria, or photosynthesizing bacteria, called gloeocapsa magma (glow-ee-oh-cap-sah maag-mah). The bacteria feed on the materials in asphalt shingles and develop dark UV protective coatings which are the source of the black streaks.
Beyond being an eyesore for homeowners and prospective buyers, the bacteria have the potential to do lasting damage to the roof. Organic materials like gloeocapsa magma retain moisture which can degrade the roof over time and obstruct the water repellant properties asphalt is often chosen for. Additionally, they block the roof’s heat reflective properties which can not only break down shingles faster but can drive up your cooling bill too, especially during warmer months.
So what is to be done about these pesky bacteria? The simple answer is regular roof cleanings done by a professional. Preventing the buildup of gloeocapsa magma is the best way to avoid spendy roof repair projects in the future. Having this cleaning done by a professional also ensures an expert can inspect your roof for any damage the bacteria may have caused and recommend an inexpensive solution. While the frequency of these roof cleanings varies house to house, it is good to consider the climate in which you live and how humid it is. Gloeocapsa magma grow faster in wetter climates, so homeowners familiar with humidity should have their roofs cleaned more frequently.