How to Remove Black Roof Stains

Our home is 10 years old and the asphalt roof shingles are starting to stain badly on the north exposure. Is there something that we can use to clean off the staining and treat the shingles to prevent further staining?-Tim

Hi Tim,

Your stains are probably caused by the airborne spores of a blue-green algae known as Gloeocapsa Magma, which is often mistaken for mold or mildew. While doing little harm to your shingles, the black streaks caused by the algae are unsightly.

Algae can be killed and the stains removed using chemical cleaners, though they usually return over time. Use a cleaner specially made for killing algae, or by spraying a mixture of one part bleach to four parts water with TSP (trisodium phosphate) or other detergent added in a garden pump-up sprayer. Allow the bleach to remain on for 15 to 20 minutes, then rinse it off with a hose.

Note that bleach may kill or damage plants, so wet down or cover any shrubs or flowers that will come in contact before starting. Repeated use of harsh chemicals or pressure washing can damage or shorten the life of your shingles.

Once the roof is clean, consider installing strips of zinc or copper—which are toxic to algae—along your roof below the ridge. Molecules of the metal will then wash down the roof each time it rains to keep new algae from forming. A better solution is to specify algae resistant shingles, which have copper granules embedded in them, the next time you have your roof replaced.

For more information, check out our article on How to Remove and Prevent Algae Stains on Asphalt Shingle Roofs.

Good luck with your project,



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9 Comments on “How to Remove Black Roof Stains”

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  • Pam Says:
    March 20th, 2018 at 11:39 pm

    We live in the NW by a salmon creek. We have found that a light sprinkling of dry baking soda on the black mold on a dry day eliminates the mold when the rain returns. We purchase the baking soda from Costco and use a battery powered flour sifter to spread it on the roof surface. It is not costly. It doesn’t kill plants or our protected salmon. After the next rain the roofs are restored to their previous color as the baking soda disolves. It does take a person who is agile, not afraid of heights, and in our case younger than 70 since our roofs are multi-level and our buildings two stories high!

  • Jim McIntyre Says:
    May 23rd, 2017 at 11:44 pm

    Hi Dennis, After my new roof was on for about 1 year I read about this algae problem. I ordered and installed the zinc under the first row of shingle. Its now about 4 years later and today after cleaning the gutters I can see algae and moss growing on bottom 6 foot of roof which is only about 25 foot peak to bottom. Should I add a second roll of copper about 1/2 way down roof to totally prevent this problem as black streaks are starting to develop also. I think I would try copper this time cause the zinc flashing I see on other roofs seem to work better. If it’s more costly it will be worth it to get rid of problem once and for all. Thank You Jim Mc.

  • Greg Neumann Says:
    October 30th, 2016 at 12:05 pm

    I had bad black roof stains. I used Just plain ole concentrated bleach in an ortho dial n spray. I use The richest setting which gets me around 15 to 1 ratio. Kind of weak, but very fast application. Did it 3 times in one year. It took a full year,. Stains are now gone. Now I Do it once a year. Pro’s :Cheap and easy! Cons: takes time for stains to go away (year).

  • David Shepheard Says:
    June 12th, 2016 at 11:29 am

    I suspect the solution in this article didn’t work for some because it is 25% bleach. If the Algae is heavy, a 50% solution will work better. After cleaning, a product such as “Wet and Forget” should further fade the black stain that may remain and inhibit for a time the return. On the question of why the algae is so widespread now vs 20 or so years ago, suspicion is that it goes back to the change in the materials in roof shingles in the 80’s when the base material in shingles was changed from rag felt soaked in asphalt to a fiberglass mat base. The weight was reduced so much that a filler (calcium) was added to keep the shingles from blowing off. The calcium provides a growing medium for the algae that the old asphalt did not. I would like to hear more from an expert on this theory.

  • Dana Says:
    April 19th, 2016 at 1:54 pm

    I too had disappointing results with this formula and a simple garden hose rinse. I had to get out the pressure washer to really clean the roof but needed to use caution to not damage it. Not to mention the danger of using a pressure washer on a pitched roof. These are tough stains to completely remove as the algae is embedded deep in the shingle grit. If I were not selling the house I’d be installing copper flashing to prevent having to do this repeatedly over time eventually wearing and damaging the roof.
    Wondering why this is so prevalent in the North East now? I don’t recall this problem 15-20+ years ago.

  • tommy Says:
    September 14th, 2014 at 9:35 pm


  • Bob in humid Florida Says:
    November 7th, 2012 at 4:46 pm

    Hi Danny.
    The northside of my roof was very black with algae, and had lichen in some places as well. I tried a specialty roof cleaning product, and then used the chlorine based formula with TSP you provided. While the specialty did work somewhat, the chlorine bleach formula worked hands down! I learned right away that little to nothing happens by simply trying to rinse either product off with a garden hose. In fact, I could not see any difference from my original black roof by simply rinsing. What really worked was using the “flat” position on my multi-position hose faucet end, holding it about 6 inches from the shingles. The difference was immediately evident, and pretty astounding, and the end result is that my old black roof looks almost new again. I’ll add that I didn’t notice any damage being done to the shingles by my “high pressure” flat position garden hose system, with a basic faucet pressure of 50 psi, probably double by using the flat position. This is time consuming work, and it took me 3 days to complete my roof at a cost of about $30 in chemicals (bleach, TSP). BTW, if I had continued to use the specialty roof cleaning at $25 a gallon (making 9 gallons finished solution), my project would have cost me about $150. My neighbor down the street was recently charged $1000 to have his entire roof cleaned, and we both agree that my roof turned at better, even though his “pro” used a much higher water pressure than I used, at the risk of damaging his roof (the special cleaner stated to use 300 psi). Thanks for the tip on the cleaning formula, as it saved me a lot of money and my roof now looks great!

  • Official Comment:

    Ben Erickson Says:
    July 6th, 2011 at 9:13 am

    Hi Dennis,
    While the bleach mixture will kill the algae and lighten the stain, it will take time to fade away and algae growth will come back over time if preventative measures aren’t taken. Check out the photo of the cleaned roof in our article on How to Remove and Prevent Black Algae Stains to see how my roof looked after I cleaned a section of it using the bleach/TSP formula. While it didn’t look like new, it was a lot better. Also, note the lack of stains below the metal flashing, which is basically the same as the zinc or copper preventative. Your best bet in the long run is to use shingles that are made not to stain when you replace your existing roof. Good luck with your project.

  • Dennis Says:
    July 5th, 2011 at 7:48 pm

    I used this mixture on my roof twice in two days with no results.I mixed it properly,I followed directions exactly two times and it just did not work.Kinda disappointed me.Alot of work for nothing.Sorry ,but this is a true comment.

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How to Remove Black Roof Stains