What are those black stains on my roof?

The roof stains or black streaks that you see on your roof is simply an algae that's using the limestone filler in your shingles as a food source. I live in West Chester, PA and bought my first home in 2002. Never do I remember any black stains on my roof or any of my neigbors homes. Being in the exterior cleaning business, I quickly began to notice these stains starting to appear on the northern side of many homes in Chester & Delaware County PA. After researching the issue, I learned that this was always a problem in the Gulf states, but with the moisture and humidity in recent years, this type of algae has unfortunately found a home here.

My first instinct was to simply take a pressure washer to it, but that would obviousely remove those little granules that are on the shingles and would actually shorten the lifespan of the roof. I then found out through ARMA, which is the Asphalt Roofing Manufacturers Association, the proper way to remove the algae from the shingles.

There are several ways to clean a roof, but it quickly became apparent that for immediate results, it's best to use the suggested method of cleaning that the shingle manufacturers (GAF, Ownes Corning, etc.) recommend. In addition, the Roof Cleaning Institute of America certifies its members under the condition that they only use this roof cleaning system. It produces immediate results, which typically lasts 3-5 years, and until we hear of an alternative method that produces the same results, we'll continue to follow the ARMA and RCIA guidelines.

Mike Trafficante - owner of Premier Power Wash & Roof Cleaning