Has your roof gone streaking? Are you starting to notice ugly black streaks on the roof and wonder what they are? People often mistake the black streaks on the roof for mold, mildew, or soot. But it’s a hardy type of algae called gloeocapsa magma (aka blue-green algae.) Let’s take a look at some common questions about roof streaking.

How did I get algae on the roof?

Algae spores are airborne and are carried by the wind, animals, or even on clothing. Because of this, they can quickly spread from rooftop to rooftop. As the algae accumulate, it develops a dark, hardened outer coating causing the black streaks you see. Each year you’ll notice the streaks getting darker and darker if left untreated.

Does weather and location cause roof streaking?

Location and weather are a factor in algae growth on shingles. Roof discoloration can happen anywhere in the U.S. But homes in coastal, warm, and humid climates tend to create the friendliest environments for algae growth. Also, north-facing sides of the house and deeply shaded homes are especially at risk.

Why do shingles get algae?

Roof algae are more common today than in the past. Traditionally, asphalt shingles got their name because they were mainly asphalt, oil-based products, and felt materials. But today, most shingle manufactures have switched to shingles containing asphalt, but mostly made up of filler such as fiberglass and crushed limestone, which encourages algae growth. Crushed limestone is the algae’s main food source.

Are the black streaks on the roof harmful or dangerous?

Roof algae are not harmful or dangerous to you. However, it can be to your roof if left untreated. The algae can cause the protective UV granules that cover the shingles to come off, causing them to dry out.

Fungus, which is also airborne, can combine with the algae and form into lichen. This lichen feeds off of the algae and the shingle filler. Lichen can develop roots which makes it harder to remove.

Which types of shingles are most at risk?

Blue-green algae mostly affect asphalt shingles but can be a problem for other shingle materials too.

How can I prevent it from getting worse?

You can prevent roof streaking from getting worse by installing zinc or copper strips along with the top part of the shingles. When it rains, a solution will run down the roof’s shingles and prevent the new growth of moss, algae, and fungus.

How can I get rid of the algae?

Get rid of the black streaks on the roof by cleaning it yourself or hiring a professional roof cleaning service to eliminate the ugly black stains on your roof. If you decide on a DIY project, home improvement expert Bob Villa recommends this formula.

  • 1 cup of trisodium phosphate (available at hardware stores)
  • 1 gallon of bleach
  • 5 gallons of water

Caution! Do NOT use a pressure washer, even on its lowest setting. One wrong angle and you can cause damage to your shingles. 

Are any shingles algae-resistant?

Yes. If you’re replacing your roof, ask your roofer about asphalt shingles with streak guard protection. They are the most effective at reducing gloeocapsa magma algae growth. These shingles have algae-resistant mineral granules that incorporate metals, such as copper-lined mineral granules, to reduce algae growth.

Prevent roof streaks before they start with a roof a tune-up and extend the life of your roof. Has your roof gone streaking? A streaking roof is a roof that needs some TLC. Or do you need a roof repair or replacement? We can help. Contact Perry Roofing Company today! 479.306.4327