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Black Streaks and Staining on Your Roof

Sep 6th, 2016 // Blog

Is your home’s roof line marred by unsightly black stains and streaks? This eyesore — common in humid environments, such as the Indianapolis area — is more than just an ugly sight. In fact, few things are more damaging to your home’s asphalt shingles. So what causes the black streaks and stains, and what can you do about it? The experts here at Bauerle Roofing give you the run down on these mean streaks.

What causes the black streaks and staining on your roof?

A lot of people assume that the black streaks and stains on asphalt shingle roofs are caused by dirt, but the culprit is actually a living organism.

A cyanobacteria known as gloeocapsa magma, or simply “GM,” is to blame for those unsightly marks. GM — which is a form of mold or fungus — is spread by airborne spores. It thrives through photosynthesis, and by feeding off the limestone composite and filler found in most asphalt shingles.

The black staining is more commonly found on the north- or east-facing roofs, due to the protective coating the GM grows to shield itself from UV light. However, the same organism appears blue-green in no- or low-light areas of the roof. GM also prefers cooler, shady areas of the roof where moisture is present.

What problems do the black streaks and staining on your roof cause?

While some say black streaks and stains are just an aesthetic issue — it actually opens your roof up to serious problems that are more damaging than bad curb appeal. The presence of GM on your asphalt shingle roof often leads to the development of lichen or moss.

Lichen’s roots wrap about the granules in the shingles, and once it is anchored into the shingle it is very difficult to remove. Even when dried out, it can be rejuvenated and by moisture. Moss and lichen retain moisture — holding it close to your shingles. This can be especially damaging during the winter months when the water freezes.

What can you do to remove and prevent black streaks and staining on your roof?

It may be tempting to try to remove the GM-caused streaks and stains yourself, but don’t risk it. You not only put yourself in a dangerous situation by climbing up on the roof, you may also cause more harm to your roof than the GM.

Asphalt shingle roofs should never be cleaned using a high-pressure washing system, as the force of the water blast severely damages asphalt shingles.

Copper- and zinc-coated sheet metal is toxic to GM, and it can help kill existing organisms and prevent any future problems. Attached to your roofline, the ions in the metal strips are washed down the roof during a rain storm. The copper or zinc ions attach to the GM and keep it from thriving and growing.

If it’s time to re-roof — and you know your home is prone to black streaks and staining — there are asphalt shingles available with built-in algae-resistant granules.

Prolong your roof’s lifespan and enhance your curb appeal. Contact the experts at Bauerle Roofing today for a free evaluation and to discuss your options 317.985.2344

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