What Are Those Black Spots On My Roof?

You could have the nicest front door, the most immaculate landscaping or even the most expensive car on the block in your driveway, but if your roof isn’t in good shape it could make all else seem futile. We’re talking about those dark spots and ugly black streaks that may look like dirt or soot — they need to go. But where did they come from in the first place and how can you get rid of them? Find out below!

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What Causes Black Spots on a Roof?

Oftentimes, homeowners refer to those ugly black spots or “stains” on their roof as dirt, mildew, soot or mold. However, it’s actually caused by algae. Algae spores are airborne and they commonly land on and stick to roofs where they quickly grow and spread. 

But, why does it look black? Well it’s actually blueish-green in color, but it has the ability to form a protective barrier against UV rays, which is generally black in color.

Why Does Algae Grow on Roofs?

Back in the day, asphalt shingles were primarily made of asphalt. Today, lots of shingle manufacturers have switched over to a combination of asphalt, fiberglass and crushed limestone — all of which encourages algae growth. 

With that said, you will likely notice algae growth on the northern-facing slopes of your roof. This is typically the darker and wetter side of the roof which happens to be the ideal breeding environment for algae.

How Can I Remove Algae From My Roof?

While algae growth on your roof isn’t necessarily preventable, it can be removed rather simply if/when it does begin to grow. A simple roof cleaning, or roof shampoo, is likely all you need in order to get rid of the black spots. Most roof cleaning solutions contain a combination of chlorine bleach and/or trisodium phosphate.

While occasional roof cleaning with chemical cleaners won’t cause too much harm, it is important to note that repeated exposure to chemicals can cause aesthetic and structural damage over time. 

Roofing Services in Nassau & Suffolk County

At Preferred Exterior, we are a full service commercial, industrial and residential roofing company. We have built a solid reputation of performing high quality roofing and exterior work at very competitive prices, serving Nassau, Suffolk, Queens, Brooklyn, Bronx, New York and the Tri-State area for over 50 years.

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