What is the Black Stuff on My Roof and How Do I Remove It?

You’re pulling into the driveway after a long day at work when it hits you: the sight of those ugly, black stains on your roof. You have no idea what they are or how they got there. Even worse, you have no idea how to get rid of them. Well, you can take some comfort in the knowledge that you’re not alone. What you see on your roof is fairly common. We have plenty of experience dealing with it as well.

Black Streaks on Roof

The first thing to note is that what you’re seeing is the result of a cyanobacteria known as gloeocapsa magna. It’s also known as blue-green algae in the roofing business. Though gloeocapsa magna has literally been around for centuries, it didn’t make its ugly presence known as a major problem in the U.S. until the postwar building boom of the 1950s. Since the 1990’s, gloeocapsa magna has spread to just about every corner of the United States.

The Effects of Gloeocapsa Magna

The gloeocapsa magna bacteria makes its way to roof tops as algae spores carried by the wind, squirrels, birds, and even insects. Once on the roof, the bacteria begin to feed on the limestone filler used to create the protective granules asphalt shingles are known for. The bacteria also photolyzes any moisture on the roof to produce oxygen.

Homeowners don’t recognize an infestation at first because very little discoloration is observed. But over time, black stains develop as some of the bacteria die off to create a dark, tough, protective outer coating. Gravity pulls this coating down, leaving black streaks on the impacted roof.

The Wrong Way to Remove Black Streaks From Your Roof

There is a temptation among homeowners to try to address gloeocapsa magna with power washing. This is something you should absolutely NOT do. There are three reasons for this:

  1. Power washing will not get rid of the bacteria. You may get rid of the stains, but the bacteria will continue reproducing and eventually put you right back to where you started.
  2. Power washing virtually guarantees damage to your roof. The asphalt shingles were not designed to withstand the punishment of power washing, and they won’t. You will do more harm than good.
  3. Lastly, climbing up on top of your roof with a power washer is dangerous. Roof work is best left to professionals who know how to do it safely.

How to Properly Remove Black Streaks From Your Roof

The correct method of attacking gloeocapsa magna is with low pressure or non-pressure washing using a special solution that includes sodium hydrochlorite and copper sulfate. The solution almost immediately kills the bacteria and washes away the stains. As an added bonus, it is also effective for addressing other roof top issues including moss and lichen.

Any debris that remains behind is washed away with the next rain. Any moss and lichen left behind dries up and flakes off within a few weeks of treatment. A few more weeks and some subsequent rains will leave your roof looking like the bacteria, moss, and lichen were never there.

Why You Should Have Gloeocapsa Magna Removed

Now that you know what that black stuff on your roof is and how to get rid of it, you might be left with the following question: do I really need to address it? Absolutely. Gloeocapsa magna is considered harmful to roofing materials because it traps moisture.

A gloeocapsa magna infestation will not normally go away on its own. Over time, the bacteria will reproduce and take over larger and larger portions of the roof surface. It will trap moisture that will eventually work its way under shingles to cause premature aging and potential wood rot. The protective granules of your asphalt shingles will also be damaged as the bacteria spreads.

Professional Roof Cleaning

As previously stated, we urge homeowners not to try treating gloeocapsa magna on their own. This bacteria is very prolific and difficult to get rid of if you don’t know what you’re doing. Rather, call a professional with verifiable experience.

A & J Reliable, Inc. offers non-pressure washing for gloeocapsa magna, moss, and lichen. Trust us to handle that black-stained roof for you in a way that is both safe and effective. We will rid your roof of the ugly blue-green algae in no time at all. And when we’re done, pulling into the driveway at the end of a long day will be much more enjoyable.