Roof Streaks: “The Big Black Marks”

June 12, 2015
I have heard people say that the black streaks on roofs are caused by everything from acorns cracking on the surface to tree sap or shingle degradation due to granule loss. While these might be possibilities, the fact is that in most cases, the stains and streaks are a form of algae or moss. Roof algae, commonly known as Gloeocapsa Magma, is a type of algae that thrives in humid and warm climates and usually appears first on the North slope of the roof where shade is prevalent and moisture tends to accumulate. The result is usually a black streaked roof. Roof moss is more prevalent in the Pacific Northwest and Canada and it is an actual moss growth like what can be found on a tree or rock. Roof algae and moss spores are carried by the wind until all roofs in the area are infested.
Roof moss is very dangerous because it will grow underneath the roof shingle and act like a sponge soaking up water after a good rain. Eventually the moss will cause roof leaks if not treated. Roof moss also accumulates on the North side of the home or where shade is most prevalent.
Roof algae, once attached to a shingled roof, feeds on the dead organic matter used in the manufacturing process of the shingle. As the fungus breaks down the asphalt shingle, the ceramic granules protecting the surface of the shingle are loosened and begin to fall off. This causes the roof to deteriorate prematurely and diminishes the roof’s abilities to reflect heat rays. If not treated, the roof algae will reduce the life of your roof, diminish your home’s curb appeal and increase your home cooling expenses.

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