Get A Free Consultation

If you live in the midwest you’ve probably noticed dark streaks on your or your neighbor’s roof. But what are the dark streaks on your roof and what causes them?

These dark streaks are typically visible on the north or east side of the roof. Contrary to what you might think, it’s not mold or dirt- rather staining from airborne algae. Often times people refer to this as fungus or mold, but this algae is a very common eyesore on roofs all throughout the US and especially the greater Columbus area.

Let’s break down what to do if you find these dark streaks on your roof and how to prevent them in the future.

dark streaks on roof

What Causes Black Streaks on Your Roof?

The unfortunate reality is that standard roofing shingles are quite susceptible to black streaks caused by algae growth. You may have had a roof installation in the past ten years and noticed one particular side of your home (typically north or east), the roof is dark and stained with weird streaks.

Since your roof is such a large portion of a home’s exterior, and algae is difficult and expensive to clean, the discoloration can become an aesthetic nightmare which decreases the value of a home. Even though roof streaking is caused by what’s called blue-green algae (cyanobacteria), the streaks are black due to the dark-pigmented sheath that algae uses to protect itself from the sun’s rays.

Algae can easily spread in the right conditions:

  • Wind can carry algae spores from roof to roof
  • Hot and humid conditions promote algae growth
  • Shaded areas with heavy tree growth are excellent breeding grounds

Algae discoloration most often occurs on north and/or east-facing surfaces but can show up anywhere on your roof. In fact, an algae infection typically takes hold well before the black streaking is visible.

roof algae stains

How to Remove Algae (Dark Stains) from Your Roof

If you just noticed dark stains or algae starting to form on your roof, we would recommend removing it ASAP. While the most common complaint about roof algae is that it is ugly and ruins your homes curb appeal, it can also damage your shingles and reduce the life of your roof. This is why it is crucial to remove algae as soon as you see it start to take hold.

The Best Way to Remove Algae and Dark Streaks from Your Roof

Removing roof algae is actually not too difficult. With powerful solutions like Wet and Forget, you can remove algae from your roof without any scrubbing! All you need to do is attach the bottle to your garden hose and apply it to your roof. After a few days you should start to see a difference. If not, just apply another coat and you should be good to go.

Is it too Late to Remove Roof Algae?

If you have been living with a dark streaks and algae growth for years, it is very possible your shingles are nearing the end of their life. While you can try to remove the algae, it might be best to consider replacing your roof with algae resistant shingles.

Replacing Your Roof with Algae Resistant Shingles

CertainTeed, GAF, and other shingle manufacturers have developed shingles with algae-resistant technology. These shingles are made with a blend of standard surface and copper-containing granules to create an algae resistant layer. Since copper possesses natural anti-algae properties, the copper in the granules is gradually released over time to provide a reliable, long-term protection from algae formation.

This technology helps keep your roof looking and performing it’s best far longer than your standard shingle.


One of the first shingles we suggest to homeowners struggling with algae growth are Certainteed’s algae-resistant shingles. They carry a limited warranty against contamination from blue-green algae during the first 10 to 15 years. The warranty states all algae-resistant shingles will remain free from blue-green algae during this period and will pay, without proration, the reasonable cost to replace or clean the affected shingles. All CertainTeed shingles that Best Exteriors, Inc. installs have Certainteed Streakfighter technology embedded into them!


How to Get the Most Out of Your New Roof

If you are considering replacing your roof with algae resistant shingles, make sure to also do your research when selecting a contractor to trust with installing your new roof. While your shingles will be some of the best available, a poor installation can render them useless.

If you happen to be in the greater Columbus area, make sure to give us a call at Best Exteriors! Our team of local professionals are always happy to help homeowners get the most out of their roof.

Give us a call at (614) 964-BEST or fill out our contact form to schedule a free consultation!

Drew Paetow

We’ll have you love your home project so much that people will drive by and comment on how good it looks. That is our promise to you.

Recent Articles

Work with Best & Forget the rest