Ugly black stains on roof shingles are frequently mistaken for fungus, mildew, dirt or oil, but are in fact caused by a resilient type of algae. This common problem has Increased during the past 20 years and it is showing up on roofing all over The United States.
The algae have a tendency to move from roof to roof as wind or even animals transfer the algae spores at will. The appearance of the algae is more prevalent on lighter shades of shingles that have a tendency to reflect sunlight and heat. Darker shades of shingles tend to heat up more and kill off any algae spores that try to reside on it.
Typically the appearances of the algae streaks are generally considered cosmetic in nature and do not drastically diminish shingle life, nor does the alga significantly hamper the shingles in providing water resistance.
Manufactures of shingles have come to the conclusion that the crushed limestone that they employ in the making of the shingles actually nourishes the algae and they are now taking steps to provide shingles that have an embedded chemical that will kill the algae.
There are an array of do it yourself chemicals on the market for the homeowner who wants to take action and clean the algae off their roof as well as numerous companies that specializes in such algae removal.