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Dirty Roofs in Dayton Ohio Area

You may have noticed over the past couple of years a growing number of homes with dark black streaks running down the roof. Maybe you have seen this on a friend’s roof or a relative’s roof, but beware, if those streaks are on your neighbor’s roof, your roof may be next. It may already be discolored. Those streaks sure are ugly but wait, it gets worse.

Those streaks are actually algae (gloeocapsa magma) eating the limestone filler in the shingles. This filler was added to shingles about 30 years ago when asphalt shingles were largely replaced with the heavier, more wind-resistant fiberglass shingles we have today. Algae love limestone.

You may notice that the discoloration is primarily on north-facing roofs. This is similar to moss growing on the north side of a tree. Since north-facing roofs generally get the least amount of sun, they stay wet longer from rain and morning dew day after day. This, combined with the limestone smorgasbord, creates a perfect home for any algae spores that may land on the roof.

The algae spores are not actually black when they land on a roof. If there are black streaks on only a north-facing roof, the other roof faces are probably infested also. The algae spores just have not turned black yet. They create that dark sheath to protect themselves from ultraviolet rays. Unfortunately, this dark pigment can also affect energy bills since dark colors absorb more heat than light colors.

The spread of the algae (and the corresponding black streaks) from roof to roof is likened to that of dandelions spreading from yard to yard. If your neighbor has them, you probably will too. Another similarity is the best method to get rid of them. Mowing your yard can make a lot of dandelions disappear…for a little while, but the only way to keep them gone is to kill them. The same is true for the algae on a roof.

There are numerous methods for killing the algae and there are pros and cons to all of them. The only method approved by the Asphalt Roofing Manufacturers Association, the Roof Cleaning Institute of America and the American Roof Cleaners Association involves the use of a cleaning agent composed of water, sodium hypochlorite, some general cleaners and a surfactant. This method does not involve pressure spraying the roof (never do that) but lightly spraying the cleaning agent onto the roof to kill the algae.

Pressure spraying a shingled roof removes the protective granules from the shingles and decreases the life of the roof. The algae itself will also cause granule loss as it grows. Proof of this can be easily found in the gutters of a home. A dark or black streaked area of a roof will have many more granules in its corresponding section of gutter than a section of the same roof, which has not yet turned dark or black.

Cleaning a roof can be a do-it-yourself project but it is time consuming and dangerous without the appropriate equipment. A quick online search for “roof cleaner” or “roof cleaning” in your city and state will generally result in a couple of certified roof cleaners. They can often clean a roof without even stepping onto it and should take appropriate safety precautions, which will benefit the homeowner, the property and themselves. One such certified roof cleaner is Midwest Improvement Services locally owned in Troy, OH.

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About the Author

Bill Timmerman, Midwest Improvement Service - Ohio Roof Cleaning
Troy, OH 45373
937 231 7249

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