What Causes Black Stains On Roof Shingles

Algae growth may cause discoloration on roofs resulting in brown or black streaks on a rooftop.

What causes black stains on roof shingles.

Algae is more likely to grow on shaded roof sections probably the cause of black stains on the lower roof in the photo at above right while asphalt shingle bleed through stains more often appear to emanate from single points regardless of sun or shade exposure probably the cause of stains in the photo at above left. The black spots discoloring your asphalt roof are more than likely the pervasive and prevalent algae known as gloecapsa magma. The streaks are caused by a type of algae known as gloeocapsa magma. Roofing manufacturers have tackled the problem of roof algae by creating shingles containing copper which is deadly to algae.

The algae feed on the limestone in shingles. Over time this algae accumulates developing a black outer coating which causes stains on roof shingles. Black marks became a problem about 20 years ago when manufacturers began adding limestone granules to add weight to material used to coat shingles. When that happens it is generally caused by mildew algae mold or dirt stains.

Learn more about what causes dark streaks on a roof and how to address the issue. Replacing the shingles on your roof just because you have black stains is not necessary however and you should be suspicious of any roofer that suggests roof shingle replacement as the only solution to your algae problem. These roof invaders require a moisture rich environment usually. The algae will worsen and become more noticeable each year trapping moisture and causing premature shingle aging and granule loss.

Spray the black stains first then the entire roof so the stains get a second dose. As the blue green algae accumulate they develop a dark hardened outer coating which results in the black stains you see. Algae dark stains on asphalt roof shingles. Black streaking on roofs is a common problem.

Roof experts tell our researchers that though other components are being added to shingles to hinder algae growth they still get calls to deal with black marks on relatively new roofs. The bleach degrades into salt which kills microbial growths and the sodium silicate does the same. Mix the soap and water well first then add the bleach. While the streaks do not cause a great deal of damage they can cause the shingle to age prematurely.

It is not uncommon for roof shingles to turn black over time.