How To Clean Roof Stains

Helpful tips on how to clean roof stains

(Updated Nov. 30, 2021)

gray shinglesYour 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 clean roof stains:

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 algae stains 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 on asphalt shingle roofs, making them age prematurely and will damage the shingles.

Tip #2: Prevent future algae from growing.

map of algae growthIf 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 ridge. Then, when it rains, a solution will form and run down the roof’s shingles to prevent moss growth, fungus, and algae growth.

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 full step-by-step instruction, it’s not that difficult and it’s affordable.

Tip #3: 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.

How to clean roof stains

The best way to clean your roof of unwanted moss is to simply use a broom or brush to remove the offensive green stuff. In fact, this is a good way to maintain your roof every six months or annually. It also gets the rest of the debris off your roof, too. Don’t brush too hard, though, as you may remove the necessary granules.

If you notice fungus or algae growing on your roof, there are steps you can take to clean your roof. Depending on the roofing materials, such as metal or slate shingles, pressure washing is an efficient solution. These materials are largely waterproof and are strong enough to handle the force of the water.

Using a pressure washer on architectural or composition shingles will cause damage to the roof, however. Either by washing the protective granules of the shingles or by weakening the shingles themselves. If you hit the shingles at the wrong angle, you could be shooting water under the shingles, too, causing even more damage.

Should I try roof cleaning chemicals?

Yes, you can get on your knees and get to scrubbing that algae. Just remember, that while occasionally cleaning your roof with special chemical cleaning solutions is OK, consistent use will eventually wear your shingles down. In turn, this makes your roof more susceptible to leakage. So make sure you use it with caution.

Fortunately, there are a few cleaning products on sale that are specifically made to clean moss and algae off of your roof. Here are my favorite three: Wet & Forget, Moss Out, and Hose’n Go.
But if you happen to be a DIY kind of person, then you can make a bleach solution along with trisodium phosphate and water.

Be very careful when mixing these chemicals. Here is an instruction manual on how to do it. Using a sprayer attached to a garden hose, get complete coverage of the area to make sure the roof is cleaned. You’ll want to cover other materials because the mixture can stain metal or wood and leave a filmy residue on glass.

Before trying to clean your roof on your own, please take all necessary precautions. Even if you consider yourself fairly handy, the slope of your roof can make any cleaning very dangerous, especially on a two-story home. To protect yourself – and the condition of your roof – consider contacting a roof washing contractor.

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