What Are Those Ugly Black Streaks on My Roof?

Black Streaks on the Roof Take a look around and notice if any roofs you see in the Poconos have black streaks on them… If so, guess what? You’re seeing blue green algae!

Now most people just assume those black streaks on roofs are dirt or perhaps soot. However, the reality is that gloeocapsa magma, aka blue green algae, is growing on the roof. Typically it starts with small spots, but over time develops into quite visible streaks after about two months or so.

Why Does Blue Green Algae Look Black?

Wait a minute, though. If it’s blue green algae, why does it look black? The algae actually forms a protective outer coating for itself to avoid damaging UV rays. And this coating looks black to most people’s eyes; it is a dark pigment after all.

Where are you likely to see black streaks on roofs? They especially show up on asphalt shingles. A grey roof with black streaks is all too common. Keep in mind that algae spores are airborne, so they can be carried by wind, animals and more– going from roof to roof and easily spreading around a neighborhood. Meanwhile, asphalt shingles made of fillers like crushed limestone are great food sources for algae– so they’re essentially eating your shingles.

Wherever the weather gets hot and humid you’re likely to get algae growth on shingles– even in the colder states like PA– which still do have hot spells each summer, right? The only areas in the continental U.S. where this doesn’t occur much would be out West in states like Colorado and Arizona where they have very dry weather year ‘round.

If you have dark streaks on your roof is that a bad thing? Well, that algae growth can dislodge shingles and/or dry ‘em out over time. Fungus can combine with algae to form into lichen, developing roots, and that can cause havoc with roofing. So should you get the streaks removed? Sure. They can be removed by a simple roof cleaning.

Ask Roofing by Bruce about this, by calling 570-424-8891. Or email info@brucescentral.com. Based out of East Stroudsburg, PA, Roofing by Bruce we handle roofing repairs, installations, inspections and more.