Cleaning Asphalt Shingles
Cleaning asphalt shingles is mostly due to an algae called Gloeocapsa Magma.
The algae is a blue - green strain which has has been causing problems throughout about 80% of the U.S., but especially in the more humid environments.
The growth of the algae usually occurs on the north or west side as well as shaded areas of the roof.
Furthermore, as the algae grows and decomposes, the resulting algae growth holds moisture, which accelerates its growth.
About 30 years ago the asphalt shingles were manufactured using an organic mat made of felt or other organic base composed of various cellulose fibers.
With the change in the 1970s to using fiberglass shingles, came the use of calcium carbonate (finely crushed limestone or marble dust).
The bad news is that the limestone is a favorite food source for the algae.
Often, the black or dark brown stains are mistaken as dirt, tree droppings, mold, fungus or mildew.
Beyond asphalt shingles, nearly all types of roofing are susceptible to staining and discoloration.
Lighter colored roofs are more vulnerable to having the algae apparent in the roof.
Other types of fungi and algae that can cause staining, but it is expected that 99% of roof stains are caused by Gloeocapsa Magma.
In some parts of the U.S., moss build up is a problem as well.
To clean the roof from stains, whatever the cause, one of the best and most honest guides, which was one of the main sources for the information on this page, is available at
For example, the PDF report takes a good look at Asphalt Roofing Manufacturers Association Technical Bulletin- Algae Discoloration of Roof, and the problem it contains.
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