How To Prevent Black Streaks from Appearing on Your Roof

How to Prevent Black Streaks from Appearing on Your RoofYour roof is one of the most important features of your home and taking great care of it will help it last longer. During your regular maintenance of the roof, have you noticed that black streaks have started to appear? They often show up on shingled roofs. Even though these streaks won’t cause immediate harm, they can cause the shingles to age prematurely. Here are some helpful tips on how to prevent black streaks from appearing on your roof:

Tip #1: Know what the black streaks are.

Black streaking atop roofs is usually made up of algae called Gloeocapsa magma. Over time, it will develop a dark and hardened outer coating, which allows for the black streaks that you see on the roof. The algae will feed on the limestone in the shingles and if it’s not taken care of, it will get more and more noticeable. It will continue to trap moisture and cause granule loss in the shingles, making them age prematurely.

Map of Algae Growth in the United StatesTip #2: Prevent future algae from growing.

If it’s not time for a roof replacement and if you want to just help stop more algae from growing on the roof, you can install zinc or copper strips along the top part of the shingles. Then, when it rains, a solution will form and run down the roof’s shingles to prevent moss, fungus, and algae from continuing to grow. It’s important to note that this won’t remove the algae that is already there – it only prevents new growth. In addition, avoid using bristle brushes or power washers, as these can cause the UV-protectant granules on the roof to wear away.

Here is a link describing exactly how to do it at Ask The Builder. They will provide a full step by step instruction, it’s not that difficult and it’s affordable.

Tip #3: Try a Chemical Cleaning.

Yes, you can get on your knees and get to scrubbing that algae. Just remember, that while occasionally cleaning your roof with special chemicals is OK, eventually with consistent use, your shingles will start to wear down, making your roof more susceptible to leakage. So make sure you use with caution.

Fortunately there are a few cleaning products on sale that are specifically made to clean the green off of your roof. Here are my favorite three, Wet & Forget, Moss Out & Hose’n Go.
But if you happen to be a DIY kind of person, then you can make a simple mixture of bleach, trosidoim phosphate and water. Be very careful when mixing these chemicals. Here is an instruction manual on how to do it. 

Tip #4: Replace the roof.

Is your roof more than 20 years old and the black streaks have started to take over? It may be time for a new roof. When you go to replace your roof, re-shingle the roof with algae-resistant shingles. This will help prevent streaks from returning in the future and will help your roof last longer.


Proper roof maintenance is incredibly important and if you don’t keep up on it, it could be a very costly and time-consuming mistake. Roof repairs and roof replacement can be a big hit to your finances, so keeping on top of preventative maintenance will benefit you well into the future. In addition, have a professional roofing specialist inspect your roof on occasion. These professionals have the experience and expertise to notice the signs of roof damage before you might notice them.

Have questions? Contact us today!

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