Black streaks forming on existing roof

Old 07-16-02, 07:12 AM
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Black streaks forming on existing roof

Could not find another place to put this.
Anyone have an answer for why these black streaks form?
Can they be cleaned off?
Is it a sign of a rapidly deteriorating roof?
Old 07-19-02, 08:18 AM
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Unhappy Fungus / Algae

The black streaks forming on your roof are most likely a form of fungus or algae. If so, it is not deteriorating your roof.
Why and where it forms is pretty much a mystery. It is an airborne disturbance that will pick a house and land on it. Once it lands, it spreads very rapidly and can turn your roof completely black. It almost always starts on the north face of most roofs... don't know why.
We DO know that fungus/algae doesn't like certain products in leads and other metals such as zinc and copper. You may notice that this fungus/algae will not grow under any turbins, lead pipes, or metal flashing on the roof. That is because the rain hits this and washes down the roof keeping the fungus/algae from growing.
The good news is that it CAN be cleaned off with a bleach/water solution. The more bleach the better, but watch for the runoff on your landscaping. Bleach and flowers do not mix well. The unofficial mix to use would be 1/3 bleach, 1/3 water, and 1/3 TSP (Tri Sodium Phosphate - common detergent).
There is a company named Chicago Metallic that makes a product called "Shingle Shield" that is made specifically to clean roofs. They also have a "zinc strip" that can be installed to keep the algae from returning once cleaned.
TAMKO Roofing Products also has a system called "Roof Reclaim" that cleans and protects your roof from algae and then gives a warranty. You can find out more about that at .
To find out more about fungus/algae, the Asphalt Roofing Manufacturers Association (ARMA) has technical bulletins on their website. You may want to check them out.
Good luck.

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