Black Roof Stains?

Black Roof Stains? Check for Algae! - Image 1


Black Roof Stains? Check for Algae! - Image 2


The black spots discoloring your asphalt roof are more than likely the pervasive and prevalent algae known as Gloeocapsa magma.

Black Roof Stains? Check for Algae! - Image 3

Bleeding due to algae caused deteriorating

Bleeding of bituminous (the main ingredient in asphalt) material was readily identified as a surface stain or discoloration on the roofing membrane. Loss of bitumen might signal a reduced roof shingle life for two reasons:

  1. Shingle bleeding stains may be a clue that the asphalt mix for the particular shingle batch lacked adequate bonding due to the algae.
  2. The loss of substrate material (the cohesive material) from a shingle may correlate with aging and wear.

A change in shingle weight is the dominant feature appearing in shingle wear. Loss of weight caused by loss of surface materials or loss of membrane materials correlates with shingle wear and life span. Loss of volatile materials is significantly lowers the flexibility of shingles which is another contributing factor to shingle wear and ultimately leads to tears or cracking.

Do you live in an area likely to get algae? 

Here in Allentown, Pennsylvania, as you can see by the key on the map below, we have a serious problem, which means we are pretty likely to see these streaks appear across all our shingles roofs across the state. 

Black Roof Stains? Check for Algae! - Image 4

Does roof algae growth on asphalt shingles affect shingle life?

Two claims of harm caused by roof algae:

  1. Roof algae causes shingle granule loss? Black algae reduces roof shingle life by “eating” at the shingles which loosens mineral granules and exposes the shingle substrate.
  2. Roof algae causes shingle tab lifting? Black algae on roof shingles is a cause of shingle tab lifting.
Black Roof Stains? Check for Algae! - Image 5

Should you clean your shingles?

Watch Out! Don’t try to clean your asphalt shingles roof without consulting the manufacturer about their recommended cleaning methods. For example, power washers and chemicals may damage the shingles and reduce the life of your roof. Other chemicals such as bleach may cause staining on other areas of your building and can be unsafe if not handled properly.