The cause of black streaks on your roof

Black streaks on roofs are a common problem that homeowners face. These dark stains can ruin the appearance of your home and make it look unkempt. In addition to being unsightly, black streaks can also cause damage to your roof, reducing its lifespan and requiring costly repairs. But what is the reason for these black streaks to appear on your roof? In this article, we’ll explore the various factors that lead to roof streaking, from algae growth to environmental factors, and provide some solutions for preventing and removing these stubborn dark stains. 

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Disclaimer: The information provided in this article is intended for general guidance and should not be used as a substitute for professional advice or services. While we strive to provide accurate and up-to-date information, we cannot guarantee that the information contained herein is correct, complete, or current. Additionally, when it comes to specific roofing needs and solutions, it is always best to seek the advice of a licensed contractor or roofing specialist. If you are in need of roof cleaning or repair services in the Spokane, WA area, we recommend contacting Advance Roofing LLC at for reliable service and expert advice.

Why do black streaks appear on roofs? 

Black streaks on roofs are a common issue that homeowners face. The primary cause of these streaks is algae growth, which can occur on any roof surface. This growth is often fueled by airborne spores that are spread easily through the air. Once these spores settle on the roof surface, they can quickly take hold and begin to proliferate, leading to the appearance of black streaks. 

The filler materials used in asphalt shingles are particularly conducive to algae growth, as are the humid conditions that are often present in many areas of the country. North facing roof portions are particularly prone to black stains, as they are the areas that receive the least amount of sunlight, which creates an ideal environment for algae growth. 

To prevent black streaks from forming on your roof, regular cleaning and maintenance are essential. There are several methods for cleaning a roof, including the use of pressure washers, power washers, and garden hoses. Algae-resistant shingles can also be installed to prevent the growth of algae on the roof surface. In addition, the installation of zinc or copper strips can also help to inhibit the growth of algae and prevent black streaks from forming. 

Algae Growth

Algae Growth

One of the common causes of black streaks on roofs, particularly asphalt shingle roofing, is Algae growth. Algae are microscopic organisms that thrive in humid and shaded areas, making your roof an ideal environment for them to grow. Once they are established, they can spread quickly, leaving black or dark streaks on your roof. These streaks can be unsightly and can even reduce the lifespan of your roof. In this section, we will explore the causes of algae growth, how to prevent it, and the best ways to clean your roof if algae has already taken hold. 

Gloeocapsa Magma 

The black streaks that appear on asphalt roofs are caused by Gloeocapsa Magma, a type of blue-green algae. The algae produces a dark pigment that makes the streaks more visible as it grows. Over time, the algae can cause premature aging and damage to shingles, which can potentially lead to leaks. 

It’s important to remove Gloeocapsa Magma as soon as possible to prevent further damage. While it’s tempting to use a pressure washer or bleach to remove the black stains, these methods can cause more harm than good. Pressure washing can damage shingles and dislodge granules, while bleach can strip shingles of their protective layers and leave them more vulnerable to algae growth in the future. 

Instead, consider using a mixture of water and oxygen bleach or hiring a roofing professional who uses specialized cleaning solutions and equipment. In addition, roofing manufacturers now offer algae-resistant shingles with copper granules or zinc strips that can prevent the growth of algae on roof surfaces. Proper maintenance and cleaning can extend the life of your roof and help it maintain its appearance. 

Algae-Resistant Shingle Roofs

Algae-Resistant Shingle Roofs

One effective way to prevent black streaks from forming on your roof is to invest in algae resistant shingle roofs. These shingles contain copper granules that act as a natural deterrent to the growth of algae on your roof. Copper is known for its toxicity to organic material, including the algae that often forms on roofs, and it effectively reduces the likelihood of black streaks forming. 

Using copper granules in algae-resistant shingles is an affordable option compared to installing copper strips, making it a more accessible solution for many homeowners. By opting for algae-resistant shingles, you can save on the costs of periodic cleaning services while enjoying a lasting solution that prevents black streak formation. With algae-resistant shingle roofs, you can rest easy knowing that your roof will remain clean and streak-free for longer periods, without the need for constant maintenance and cleaning. Invest in algae-resistant shingle roofs for a more effective and affordable solution to protect your roof from black streaks caused by algae growth. 

The Role of Copper Granules and Copper Strips 

Copper granules and copper strips are materials used to inhibit algae growth on roofs. These materials act as a natural biocide that prevents algae from taking hold on your roof. Copper is toxic to algae and other organisms, and the copper granules or strips release small amounts of copper ions onto the roof surface when it rains, which kills algae and prevents it from growing. 

Copper granules are typically embedded in asphalt shingles, while copper strips are attached near the roof’s ridgeline. The copper granules in asphalt shingle roofs gradually release copper ions, which run down the roof over time and inhibit algae’s growth. On the other hand, copper strips are installed on the roof’s ridgeline and slowly release copper run-off that spreads out across the roof’s surface. 

While copper and zinc are considered natural elements, there are potential environmental impacts to using them on roofs. Run-off from copper and zinc strips can harm aquatic life in nearby streams or ponds. Additionally, excessive copper could increase soil acidity levels, potentially reducing plant and microbial activity. However, studies show that these environmental impacts are generally minimal, and copper and zinc strips are an effective, safe way to inhibit algae growth on roofs.

Cleaning Solutions for Black Streaks on Your Roof 

Black streaks on your roof can be a frustrating and unsightly problem that many homeowners face. These dark stains are caused by the growth of algae, which can thrive in wet, humid conditions. While there are a variety of preventive measures that can help keep algae at bay, once it has taken hold on your roof, cleaning solutions become necessary to remove it. With the right cleaning products and techniques, you can safely and effectively remove black streaks from your roof, restoring its appearance and protecting it from further damage. 

Pressure Washer or Power Washer 

Pressure washers or power washers are a popular option for cleaning roofs due to their efficiency and speed. However, caution is necessary to avoid causing any damage to roofing surfaces. While pressure washing may be suitable for metal roofs, it should not be used on shingle roofs, as it can cause granule loss and void warranties. 

It is essential to consult a roofing professional before using a pressure washer or power washer on any roof surface. A professional can advise on the appropriate cleaning method and solution specific to your roof type, ensuring no damage is caused during the cleaning process. In summary, while pressure washing can be the fastest and most efficient way to clean roofs, it is necessary to exercise caution to avoid causing any harm to roofing surfaces and risking costly damage. 

Garden Hose with Detergent Solution

Garden Hose with Detergent Solution

Black streaks and algae stains on your roof can be unsightly and even cause damage to your roof. Fortunately, a simple solution of detergent and clean water can effectively clean and remove these stains with the help of your garden hose. 

  • First, mix a solution of detergent and clean water in a garden sprayer. 
  • Make sure to use a detergent that is safe for your roof and will not cause damage. 
  • Spray the solution onto your roof and let it sit for at least 15 minutes. 
  • This will allow the solution to penetrate the stains and loosen any dirt or debris. 
  • Next, rinse the roof with a garden hose, starting at the top and working your way down. 
  • Be sure to use low to medium water pressure to avoid damaging your roof. 
  • The combination of the detergent and water will effectively remove the black streaks and algae stains from your roof, leaving it looking clean and new again. 

Using a garden hose with a detergent solution is a cost-effective and easy way to clean your roof and remove black streaks and algae stains. Regularly cleaning your roof can also help prevent future growth of algae and other stains, extending the life of your roof.

Chlorine Bleach Mixture 

Cleaning your roof with a chlorine bleach mixture can effectively remove dark stains and black streaks caused by algae growth. To create the mixture, mix sodium hypochlorite (chlorine bleach) and sodium hydroxide with trisodium phosphate (TSP) to create a powerful formula. 

Using a pump sprayer, apply the solution to your roof, making sure to fully saturate the affected areas. Allow the formula to dry for 15-20 minutes, then apply a second coat, ensuring that the entire roof surface is covered. 

Be careful when handling bleach and wear safety equipment to avoid injury or irritation to the skin and eyes. Make sure to also protect any foundation plantings by covering them with a tarp or watering them thoroughly before and after application. 

After applying the bleach mixture, rinse the roof thoroughly with a garden hose to remove any remaining dirt or debris. Remember to use low to medium water pressure to avoid damaging your roof. This method is effective in removing algae stains and black streaks, leaving your roof looking clean and new again. 

Commercial Cleaners and Solutions 

There are several commercial cleaners and solutions available for removing black streaks on roofs. It is important to select a product that is specifically designed for roof cleaning and not just any household cleaner. Choosing the right commercial cleaner can make a significant difference in the effectiveness of the cleaning process. 

  • One of the most popular commercial cleaners for roof cleaning is an oxygen bleach solution. This type of solution is effective for removing black stains on roofs caused by algae. It is also environmentally friendly and safe for use around plants and animals. 
  • Another option is a chlorine bleach solution. While this can be effective for removing stains on roofs, it can be harsh and corrosive. It is important to handle it with care and protect any surrounding vegetation. 
  • There are also commercial cleaners that come in a spray bottle and can be easily applied to the roof surface. These cleaners often contain ingredients such as sodium hydroxide, which can be effective for removing dark stains on roofs. 

It is important to select a commercial cleaner based on the severity of the staining and the type of roof you have. Some commercial cleaners are designed specifically for use on shingle roofs, while others may be more appropriate for metal or tile roofs. 

Professional Cleaning Services

Professional Cleaning Services

Hiring professional cleaning services for your roof can have both benefits and drawbacks. One benefit is that professionals have access to more effective and safer cleaning solutions, as well as the necessary equipment for the job. This can result in a more thorough and efficient cleaning process. Additionally, it can reduce the risk of damaging your roof since professionals have experience in working with different roof materials. 

However, hiring professionals can be more expensive than DIY methods. It is important to keep in mind that the cost will vary based on the size and condition of your roof. Despite the cost, hiring professional cleaners can save you time and effort. Instead of spending time researching and purchasing cleaning solutions and equipment, professionals can complete the job quickly and efficiently. 

Overall, the decision to hire professional roof cleaners should be based on personal preferences and budget. While it may be more expensive, the benefits of a thorough cleaning and reduced risk of damage may outweigh the cost for some homeowners. 


Black streaks on your roof can have a number of causes. While some DIY methods exist for removing the stains, it is important to carefully research and select the right cleaning solutions and techniques to avoid damage to your roof. Additionally, hiring professional cleaners may be more expensive but could result in a safer and more thorough job overall. 

Answers to Your Questions About Removing Black Streaks from Your Roof

What causes black streaks on roofs?

Black streaks on roofs are typically caused by algae that thrives in damp environments. The algae can cause discoloration and damage to roof shingles over time.

How can I prevent black streaks from forming on my roof?

Regularly cleaning your roof and removing debris can help to prevent black streaks from forming. Additionally, proper ventilation and insulation can reduce moisture buildup which can also prevent algae growth.

Are there any DIY methods for removing black streaks from a roof?

Yes, there are several commercial cleaners available that are specifically designed for cleaning roofs. Oxygen bleach and chlorine bleach solutions are two popular options for removing black stains caused by algae. It is important to read the instructions carefully before using any cleaner or solution on your roof.

Is it necessary to replace my entire roof when I have black streaks?

It depends on the severity of the staining and damage caused by the algae growth. If the stains are minor or localized, it may not be necessary to replace your entire roof. However, if the staining is widespread or has caused significant damage it may be better to replace your entire roof as opposed to just repairing certain areas.