Black Streaks That Make You Shriek !

Black streaks running down your roof are a type of roof algae known as Gloeocapsa Magma. These pesky bacteria tend to cluster in groups and locate themselves typically on the north side of roofs where the lack of sun can stimulate their growth. They like to feed on limestone – a key filler ingredient in asphalt shingles.

For the ones that are exposed to sunshine, they have a unique method of survival. According to the microbe wiki at Kenyon University, when exposed to strong sunlight, the bacteria form a black/dark green sheath around itself as a form of protection from ultra-violet rays. The pigmented covering is what shows up as dark streaks on the roof.

You may have noticed that the stains don’t appear below any copper- or zinc-coated metal flashing that you may have on the roof around chimneys or vents. This is because the coating is toxic to the algae. Each time it rains, trace amounts of the metal are washed down the roof, preventing the growth in that area.

The bad news is that if your roof is plagued by algae, it’s not going to go away. Cleaning will remove the stains but they usually return. Repeated cleaning can actually cause damage to the shingles if harsh chemicals and power washing are used.

Arnold's Home Improvement uses shingles when performing a roof install that is infused with a minimum of 10% more copper-containing granules with a 3M ceramic coating that allows copper ions to release slowly over time, third party verification and a Lifetime Manufacturer Warranty that guarantees protection against black streaks! 

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