Asphalt Shingle Stains
Asphalt shingle stains have several causes and several types of preventative measures and cures.
There are many common causes of black, brown, or gray stains appearing on asphalt roof shingles.
These causes include black algae, bleed-through from the shingles, dirt, soot, and organic debris.
Of these causes, if there is 'bleeding' of the shingles, this is usually an indication of a defective roofing product.
What is sometimes confusing about these stains that the pattern of a black stain running down the roof in a widening pattern can also be a case of black algae.
There is also the case of making a judgment between an algae growing on shingles and a fungus growing on roof shingles to zoom into the root case of stains. In this regard, a collection of the stained material using clear adhesive tape followed by a laboratory analysis should provide answers.
Inspect NY has a great explanation into how to make the judgment on what is the root cause of your asphalt roofing. Their website is located at inspect-ny.com/roof/shinglestains.htm.
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