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close up of brown shingle roof with black streaks
close up of brown shingle roof with black streaks

Top Causes of Black Streaks on Roof and How To Fix Them

Have you noticed black streaks on your roof and wondered where they came from? Algae called Gloeocapsa Magma causes these black streaks. The blue-green algae feed on the limestone filler found in asphalt shingles. 

Below, we’ll explore how to prevent and remove those black streaks on your asphalt roof. If you follow the information below, you will no longer see any black stains on your roof shingles.

Pressure washing with a power washer and soft washing will make a real difference in removing dirt and black stains. So if you’re looking for answers on removing streaks on roof shingles, look no further.

What Causes Black Streaks on a Roof?

close up of black streaks on rooftop

The causes of black streaks on roof shingles include algae growth. Algae are also known as “roof algae” or black mold. Black algae on your roof grow in warm and humid areas where there is moisture and shade. 

Humid conditions, pollution, and dust can cause black streaks and algae spores to appear on roofing materials and new shingles. 

Asphalt shingle roofing may have algae-prone areas where you’ll see mildew growth. The humidity may lead to algae growth by trapping moisture via roofing materials. 

In addition, poor quality materials used during installation and improper installation practices may lead to algae stains. Inferior materials may lead to issues and black streaks running on a new roof as they cannot withstand the harsh weather when the rain hits.

Essentially, black streaks on roof shingles occur due to:

  • Algae growth
  • Pollution
  • Dust accumulation
  • Poor quality materials
  • Improper installation

Furthermore, you may see black streaks due to soot and dirt, which get trapped in your gutters or come from overhanging trees. 

Why Are Algae Common to Asphalt Shingles?

Black and green algae or hardy algae are commonly found on asphalt shingles. The gloocapsa magma algae are known as a type of bacteria that require food to survive. 

Asphalt shingles have limestone and calcium carbonate, which are often used to fill gaps on roofs and within asphalt shingles. 

Limestone-based fillers are a common ingredient of these shingles, as the material has a lower cost than other types of substances. The algae feed on and grow on these limestone-based shingles.

How Did Algae Get On My Roof To Begin With?

contractor inspects black streaks on roof and moss growth

Algae particles are often floating in the air outdoors. The wind takes it from place to place. Further, animals may carry these particles. You’ll see squirrels and birds moving from roof to roof, carrying these particles. 

The Gloeocapsa Magma can end up on the roof and shingles, as the algae love to feed off of limestone.

Generally, spores found in the air travel from one roof to another. As such, you may see multiple homes in your neighborhood with black streaks on their roofs.

How to Prevent Black Streaks on a Roof?

You can prevent algae growth on your roof and improve the curb appeal of your home. Regular cleaning and maintenance of your roof can prevent black streaks from appearing. The cleaning process is key in keeping roofs free of stains.

You can do so by regularly washing off dirt and debris with a garden hose or pressure washer. Complete inspections to guarantee that the roof surface does not have any signs of harm or deterioration, as that could result in algae growth. 

The materials you’ll need include rubber gloves for safety and goggles for eye protection. By taking proactive measures like these, you can keep your roof looking its best for years to come.

Algae-resistant shingles will also play a role in preventing black streaks on your roof. As such, you should install algae-resistant shingles on top of your roof whenever you’re updating the look of your home.

Quality materials and proper installation practices are key to preventing black streaks on a roof. Ensure that the shingles employed are of superior grade and are treated against ultraviolet radiation and other weather conditions to decrease the risk of dark streaks. 

Applying protective coatings or treatments is another great way to prevent black streaks from appearing on your roof, as it can alleviate the sun’s rays and help keep moisture away.

How Do You Get Rid of Black Streaks on Your Roof?

Can you remove algae stains and mold from your roofing systems by following specific steps? You’ll see that removing black streaks from a roof is a challenging and dangerous task that should only be attempted by professionals. 

Pressure washing or soft washing are the most common methods used to remove these stains and protect any shingles or copper and metal materials. Pressure washing involves using high-pressure water to blast away dirt, debris, and algae growth. 

Soft washing uses a low-pressure system and special cleaning solutions to break down the algae without damaging the roof. Chemical treatments and solutions are also available for removing black streaks from roofs. 

Frequently Asked Questions (FAQs)

Take a look below to learn the answers to some common questions about black streaks on roof shingles.

close up of contractor working on old streaked roof

How do I get rid of black streaks on my roof?

Use a pressure washer with a cleaning solution to treat affected areas from the bottom to the top in overlapping metal strips. 

Start at the bottom of your roof and work up in overlapping strips until all areas have been cleaned. Rinse off any remaining residue before leaving your roof to dry completely.

Are black streaks on my roof bad for the asphalt shingles?

The roofing shingles or copper strips on your roofs can become damaged if you don’t bother using a cleaning solution and a power washing method to remove algae growth. You may face poor drainage and broken shingles as well as general corrosion over time due to the black streaks on your roof.


Professional roof cleaners can help you identify the source of the problem, remove existing streaks, and provide advice for future prevention. 

With their specialized knowledge and experience in dealing with these issues, professional services are invaluable when it comes to protecting your home from black stains. Contact experts from Melo Roofing today to get an estimate on your roofing project. 

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