Friday, November 10th, 2017 by Matt Cheney
We often get many questions regarding "black streaks" that seam to appear on a roof and look like they are running down towards the eave. Blue/Green algae is a common problem that is mostly located in the southern regions of the U.S. due to our warm weather and humidity. It will show up mostly on roofs that are under tree cover or on the face of the roof that is facing north.
We recently had a customer call us from Travelers Rest with this exact problem. They were worried that the algae was harming their roof and wanted an inspection performed to determine the amount of damage. We went out to survey the roof. During our inspection, we did note that most of the algae was growing on the northern most face of the home. There were some smaller slopes that also had small amounts of algae streaking down them. After completing our inspection, we advised the homeowner that the algae was not doing a whole lot of harm to the shingles but rather helping them. Algae can form a protective barrier over the shingle that will help keep the sun's UV rays from deteriorating the asphalt in the shingle.
The downside to algae is that it can make the shingles brittle and hard to repair. Roof that have a lot of tree coverage can get lichens growing on them which will damage the shingle as they can eat into the asphalt.
Most manufacturers today will blend copper oxide into the shingles to help deter algae. The standard algae warranty is 10 to 15 years with one manufacturer actually giving a lifetime, no algae warranty. Alternatives to copper oxide can be zinc or copper strips nailed across the top of the roof. When the rain runs over these strips it washes off tiny metal particles that will kill the algae and prevent it from growing back. The final solution would be to hire a company that will "wash" your roof. A solution will be mixed that is sprayed on the roof. It will sit on there for a certain amount of time and then be rinsed off. Make sure they do not pressure wash the roof as high pressure can hurt the shingles. Typically, this process takes one day and may keep the roof clean for a short time.
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