What Causes Dark Streaks on Roof Shingles?

Home 9 Roofing 9 What Causes Dark Streaks on Roof Shingles?

The sight of black streaks on your roof may be concerning to some homeowners. These unsightly black streak marks on your shingles not only diminish the overall curb appeal of a house but can also raise concerns about the roof’s health and longevity. Is your roof dirty? Is it soot or dirt? Is it mold, mildew, or something worse?

Dark streaks on roof shingles are caused by algae growth, not dirt, mold, mildew, or soot as many people assume. The algae growth doesn’t necessarily mean that your roof needs replaced, but it is a good idea to treat the algae. 

Mysterious Dark Streaks on Roofs

Dark or black streaks can appear on various types of roofs, particularly those made of asphalt shingles. The primary culprit behind these marks is a hardy, prehistoric type of algae called Gloeocapsa magma, aka blue-green algae, which tends to thrive in warm and humid environments. These microorganisms are especially prevalent in regions with high humidity levels, making them a common sight on roofs across the East Coast. 

Dark Streak Prevention and Solutions

Regular Roof Cleaning: Regular roof maintenance is essential to prevent the accumulation of moisture and debris that facilitate algae growth. This will help eliminate dark or black streaks on your shingles.

Gentle cleaning using a mixture of water and mild detergent, or specialized roof cleaners, can help remove existing streaks and discourage future growth. Bleach is also an effective removal solution, but it can cause damage to any nearby foliage. 

Do not scrub or power wash your roof. Both can remove the granules from your asphalt shingles, decreasing their effectiveness and lifespan. 

Trim Overhanging Trees: Trimming branches and overhanging trees near the roof can reduce shade and allow more sunlight to reach the surface, thereby minimizing conditions conducive to algae development.

Professional Roof Cleaning Services: For more stubborn cases or larger roofs, hiring professional roof cleaning services can be a viable solution. These experts use specialized equipment and cleaning agents to effectively remove black streaks without causing damage to the roof.

Dark Streaks on Roof Shingles

With care, you can eliminate the black streaks of algae on your roof, but they aren’t really a concern when it comes to the longevity of your roof. However, careful cleaning can remove the streaks to maintain the roof’s curb appeal. 

Algae on Your Roof’s Shingles

There’s no need to worry if your roof starts accumulating streaks. Black streaks on your roof are just algae, not mold, mildew, dirt, or chimney soot. Having them on your roof isn’t a serious condition, but they may be something that you want removed. 


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