Why You Have Black Streaks on Your Roof and How to Get Them Off

Why You Have Black Streaks on Your Roof and How to Get Them Off

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If you step outside and take a look at your house, or take a look at other houses while you are driving down the road, you will see that many of them have black streaks on the roof. A lot of people are busy, and the hustle and bustle of life turns days into months and months into years. One day you look up at the roof and realize it needs to be cleaned. You might see leaves, sticks, and other debris, especially if you live near trees.  All of those things are easy to identify and you know where they came from. If you see black streaks, however, you may not know what they are, where they come from, or how to clean them. That is what this post is going to be about.

Black Streaks on the Roof Come From a Cyanobacteria Known as “Gloeocapsa Magma”

Contrary to popular belief, black streaks on your roof are not algae, mold, or mildew. These black streaks come from cyanobacteria known as “gloeocapsa magma.” This particular form of bacteria travels via airborne spores that are carried by the wind until they attach to a roof or other surfaces. Over time, the bacteria accumulate, especially in areas that are dark and moist. For this reason, homeowners often notice the black streaks on the north side of their roof first. In addition to dark and moist areas, humidity and higher temperatures promote further growth. This is why southern states in the US tend to see a lot of gloeocapsa magma growing on roofs.

What Happens When You Have Black Streaks on Your Roof

Once gloeocapsa magma is present on your roof, it will continue to grow and spread through photosynthesis. This bacteria has the ability to protect itself from UV rays by creating an outer coating with a dark pigment. Although the bacteria is protecting itself from the sun, it is simultaneously attracting more heat to the roof because of the dark pigment. As gloeocapsa magma spreads, the overall temperature of your roof increases.

In the southern US, summer temperatures can reach 100+ degrees Fahrenheit. On a 100 degree day, asphalt shingles could be as high 160 degrees Fahrenheit, and that is without the added heat caused by gloeocapsa magma. When you take the black streaks into account you could be approaching 180-200 degrees if not higher. Temperatures that high will destroy your shingles and degrade your roof. You will find that the overall temperature of your house increases, and your electricity bill will be higher. In Charlotte, NC  where we serve customers, homeowners could save as much as 20% on their energy bills by getting their roof cleaned.

Need Roof Cleaning in the Charlotte, NC Area?

Call Apex Exterior Washing today for Roof Cleaning, Soft Washing, Pressure Washing, and Gutter Cleaning

(704) 856-9734

How to Get Rid of the Black Streaks on Your Roof

There are many different products and tools on the market for removing black stains on your roof. Some of them simply don’t do anything to remove the stains, some of them get rid of black stains but don’t kill the bacteria completely, and others get rid of the stains and eliminate the bacteria for good. Generally, the cost of the products and the equipment needed to do the job reflect the end result.

The recommended way to remove the black stains from your roof and eliminate the bacteria completely is by using a bleach based product. Some products require one application and others require many more because the bleach mix is not as strong. The stronger mixes do a better job of eliminating the black streaks but if you aren’t careful you could harm the landscaping around your home. 

Cleaning a Roof as an Exterior Cleaning Company

If you hire an exterior cleaning company, a stronger concentration of bleach will likely be used to get rid of the black streaks. Most pressure washing companies use a 4-6% sodium hypochlorite mix to clean a standard roof. Roofs with more growth may require a higher percentage and vice versa for roofs that are mostly clean. Standard practice is to spray down all plants before and after treating the roof with a bleach based mix. Additionally, you should always have at least one person on the ground spraying all plants and landscaping around the house where the mix is running off the roof. As long as this is being done, your landscaping is fully protected from any harm. Alternatively, some pressure washing companies place sprinklers around the house to keep water on the landscaping.

Cleaning a Roof as a Homeowner

If you are going to try to clean the black streaks yourself as a homeowner, it is safer to use a ready made roof cleaning product from a home improvement store. This is because most of the ready made products won’t damage your landscape and can be used with just one person. Products that might harm your plants would require a second person to be spraying the plants with a garden hose to dilute the water before it could kill your plants.

How to Prevent Black Streaks on Your Roof

Just like there are many products for removing black stains from your roof, there are products for preventing black stains. Some of the products are actually good for both. If you want to apply a preventative product yourself, there are many ready made options at your local home and garden store. In most circumstances, your best option is going to be hiring an exterior cleaning. This will save you from having to climb a ladder or walking around on the roof. 

A professional will also be able to get the job done much quicker and without damaging your roof, gutters, or other parts of your home. Most pressure washing or exterior cleaning companies offer maintenance services that cost much less than if you call them when you have a major problem or a lot of mold, mildew, algae, or bacteria growth. Additionally, they can clean your gutters, chimney, and other things while they are on your roof if you want them to.

How Much Does it Cost for a Company to Clean a Roof

Roof Cleaning is typically priced based on sq footage, hourly rate, or with flat rate pricing. Other factors such as the amount of landscaping surrounding your home, steepness of roof, number of stories, and type of material will also affect the total cost. A standard 2,000 sq foot, one story home with average slope asphalt roof will cost around $600. That ends up being around $0.30 per sq foot and you can expect the job to take anywhere from 2-3 hours. Most exterior cleaning companies won’t get a ladder out for less than $600 because of the risk associated with the job.


No one wants to have black streaks on their roof. It negatively affects curb appeal, destroys your roof, and hurts the insulation of your home driving up electricity costs. As bad as they look, blacks streaks can be removed fully and the only way they can come back is if new spores land on your house and start to grow. Making sure the roof has been fully sanitized instead of just knocking off the surface layer of bacteria is key. At the end of the day, hiring a professional is the best way to get the job done right and doesn’t cost too much when considering the cost of home products and what you are spending on your electric bill while the black streaks are on your roof.

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