What are the Black Streaks on My Roof?

I hear it more and more lately.  What are the black streaks on my roof, and where did they come from?

The black streaks that are showing up on more roofs in West Michigan is caused by Gloeocapsa Magma. Which is a tyoe of algea that loves to feed on the limestone in the shingles. The increase in black streaks on a roof make it look like it is really dirty,and not so nice looking. There a some people that will tell you that the roof needs to be replaced when it has black streaks on it. This is just not true, and if a roofing company tells you that it needs to be, find a roofing company that is honest . This blackish algae creeps it way across neighborhood roofs, gradually turning your home’s asphalt shingles an ugly dark brown or black. Roof algae is most prevalent on north and west-facing shingles and in neighborhoods with lots of mature trees.

Why is it growing on my roof

Humidity, warmth, shade and a constant meal of limestone ensure that a bloom of roof algae will survive. The black that is seen is a cover of dead algea that protects the live algea below.

Will it harm my shingles

There is very little information as to the damage GM in itself will cause to roofing materials. Some state it is only an aesthetic problem while others state it causes damage. Both the American Roof Manufactures Association (ARMA) and Canadian Asphalt Shingle Manufacturers Association (CASMA) state that GM is only an aesthetic issue, giving a home poor curb appeal. One thing is certain, however, roofs with GM can attract other life forms that do cause damage.

When the algea is allowed to stay on a roof, lichen will begin to grow. Lichen is a photosynthetic fungus that has roots that wrap around the granules, feeding on the nutrients of the GM and the filler in the shingles.Lichen will damage shingles as they knock the granuls off and feed on the inner layer of the shingle. Once on the roof, lichen cannot easily be removed. Even if it dries out, it can come back to life when rain or moisture appears. Scrubbing or power washing the lichen will only do more damage.


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