Tips for Dealing with Black Algae Stains on Your Shingle Roof

If you notice dark stains forming on your roof that seem to streak down the shingles from the top ridge all the way down to the roof base, then you may think that the stains are produced by dirt that has washed down the top surfaces of the shingles. However, dirt is rarely the cause of the problem. The issue usually develops due to the formation of a blue-green algae that typically appears dark green to black in color. In particular, Gloeocapsa Magma is the name of the algae causing the problem. Keep reading to find out how to kill the algae and also how to prevent it from coming back.

How Do You Kill Blue-Green Algae?

If you want to get rid of the stains on your roof, then you need to work to kill the algae. If you notice the stains on the shingles, then you may see that they are more prevalent towards the middle of the roof. Typically, there will be very little of the fungi near the flashing. Most flashing is made from a mixture of aluminum and zinc, with the zinc sitting on the outside of the sheet metal. A small amount of this zinc is washed off from the flashing and it covers your shingles. The zinc stops the algae from forming, because the metal is toxic to certain types of microorganisms, like photosynthesizing fungi varieties. 

If you take a cue from the clear parts of your roof, you can use zinc to kill the rest of the algae. Specifically, you can use either a cleaning agent with a metallic salt compound or you can use a cleaner that is made with zinc sulfate. Zinc sulfate is the same type of zinc that is contained in your multivitamin. Zinc sulfate cleaners as well as metallic salts that contain zinc are safe for your roof and your home. Zinc is also found naturally in the earth, so it does not harm the environment. 

Zinc cleaners can be purchased that attach to your hose. This is a good choice if you want to safely clean the roof from the ground. If you decide to go with this spray method, make sure to cover your roof entirely and allow the cleaner to sit for at least 30 minutes. 

Once you kill the algae, you will want to get rid of the staining. While a bleach solution can be used to release the stains, bleach can lighten the appearance of your shingles. Use an oxygen bleach powder or a mixture of TSP and water. Rinse thoroughly with water when you are done. 

How Do You Prevent New Algae Growth & Staining?

It can take some time to release the stains from your roof, so continue to apply your TSP or oxygenated bleach until the streaks start to fade. If the stains do not diminish or if you have light colored shingles that make the stains appear quite prevalent, then it may be wise to hire a roof cleaning professional who can scrub the stains from the roof with a scrub brush. While you can use the same sort of tactic for stain removal, it is not safe for inexperienced homeowners to climb around on a wet roof. 

Once stain removal is completed, you can prevent new algae growth by adding a metallic ridge cap to your roof. The ridge cap is the installation that sits on the very peak of the roof. A metallic one made from either zinc coated aluminum or copper will effectively kill any forming algae, much in the same way that you flashing does. 

The ridge cap can be secured in place with either roofing nails or roofing cement. Just make sure the edges of the cap sit flat against your to prevent a runoff issue. 

For more information or assistance, contact services like The Roof Doctor.


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