What are those black streaks on my roof?
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This is a condition that exists on millions of homes across the US. The streaks are a kind of algae called Gloeocapsa Magma. It is most prevalent int Southeastern part of the country and but has been spreading North so that much of the Midwest has been affected.
The shaded side of the house will usually be the most affected side. This is due to water evaporating more slowly than it is by the shade. Gloeocapsa Magma is quite hardy and withstand extreme temperature ranges along with drought and UV. The algae loves high levels of humidity.
Although unsightly the life of the roof is not affected by the growth. The main reason for the spread of Gloeocapsa magma is because of the increased use of limestone in the manufacture of shingles. Limestone is used as a filler because it is heavy, adding to the weight of the shingle and it is cheaper than asphalt.The organism feeds on the limestone. If you factor in the moist nature of the shaded side of the house it makes an idea environment for this algae. Once the algae appears on your roof it will get more and more noticeable. The algae can be airborne and thus spreads from roof to roof.
What can you do? If your roof is not ready for replacement you can have ot cleaned by a company that specializes in this or you can do it your self. The DIY route is risky and we don’t recommend it. Many of the cleaners on the market contain bleach. You must exercise care using bleach so as to not damage your plants. The folks that offer this service usually wet down the shrubbery to ensure that it is not damaged. The streaks will return more quickly than they originally did the first time because you are not killing the spores but dying their black shells that form the streaks.
The other solution is to install zinc or copper strips near the peak of the roof. The small amount of the metal that runs off when it rains will kill the algae. You want see a change over night, but it is an effective solution.
If you are installing a new roof and want to make sure that these don’t reappear make sure that your roofing contractor installs algae resistant (AR) shingles. If this black algae is prevalent in your area then it’s probable that these kind of shingles are the only ones that will get installed. These algae resistant shingles contain some copper coated granules along with the standard mineral granules. These work in the same way that the strips at the peak do.
The greater benefit is that the copper is spread over the entire roof instead of just at the top. This will prevent the possibility of having a greater concentration of copper at the top of the roof, avoiding a lighter shade at the top than at the bottom. The copper granules on the new roof will prevent Gloeocapsa magma from taking hold on your roof along with the spread throughout your neighborhood.
