Why Do Roofs Get Streaked

Although these dark spots and ugly black streaks on your roof may look like dirt mildew soot or mold what they really are is algae.

Why do roofs get streaked. The black streaks running down roofs are actually a hardy algae called gloeocapsa magma. This cyanobacteria is a bacteria that get their strength to survive through photosynthesis and the limestone filler found in the composition of shingles. While the dark streaks are unsightly experts tell our team that the greatest danger to the roof is from moisture retention or root damage that algae and other life forms can cause. Dark streaks or roof discoloration caused by algae happens in varying degrees across the u s especially in areas exposed to warm humid conditions.

Also algae and fungus can grow together to form lichen the roots of which can wrap around and feed on the granules covering the shingles. Algae dark stains on asphalt roof shingles. As the blue green algae accumulate they develop a dark hardened outer coating which results in the black stains you see. In the past shingles were constructed using felt and asphalt.

Many people believe the streaks are caused by dirt or pollen building up on the roof but more often than not the culprit is actually an algae that is growing on the roof and feeding off the roof materials. The algae feed on the limestone in shingles. The algae is most commonly gloeocapsa magma a blue green algae that travels and propagates through airborne spores. The algae will worsen and become more noticeable each year trapping moisture and causing premature shingle aging and granule loss.

The most common type is known as gloeocapsa magma also known as blue green algae.