Home Improvement Expert Danny Lipford

How to Remove and Prevent Black Algae Stains on Asphalt Shingle Roofs

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Black stains on roof

Black stains on an asphalt roof caused by algae.

If you live in a humid area of the country, you’ve probably seen unsightly dark streaks on asphalt shingle roofs. Though often attributed to an accumulation of dirt, defective shingles, mold, or mildew; the most common culprit is actually a blue-green algae known as Gloeocapsa Magma that is spread by airborne spores.

While algae growth does little harm to roofing, the stains don’t help the overall appearance or resale value of your home.

Areas Susceptible to Algae Stains

Areas Susceptible to Algae Stains

You may also have noticed that algae stains are absent directly below the metal flashing around chimneys or roof vents. This is due to fact that copper and the zinc coating on galvanized sheet metal are toxic to algae. Every time it rains, trace amounts of metals are washed down the roof, inhibiting algae growth.

Absence of algae under metal flashing

Absence of algae under metal flashing

Algae Resistant Shingles

In recent years, roofing manufacturers have begun mixing copper granules into roofing products to produce algae resistant shingles. If you live in an area susceptible to algae growth, be sure to specify this type of shingle when replacing your roof.

Chemical Cleaning

Algae stains can be removed by cleaning, though they usually return. While an occasional cleaning might not harm your roof, repeated use of harsh chemicals, or the erosive effects of pressure washing, can damage or shorten the life of asphalt shingles.

There are several products on the market specifically designed to remove algae stains from roofs, such as Wet & Forget and Moss Out. A mixture of trisodium phosphate (TSP), bleach, and water will also remove stains. Oxygen bleach lightens stains as well and is less harmful to the environment, but it doesn’t produce as immediate or dramatic an effect as chlorine bleach.

Roof cleaned with oxygen bleach and chlorine bleach . Galvanized vent prevented algae growth.

Roof cleaned with oxygen bleach (left) and chlorine bleach (center). Galvanized vent (right) prevented algae growth.


Here’s what you’ll need to clean your roof:

  • Cleaner
  • Pump sprayer
  • Garden hose with spray nozzle
  • Safety glasses or goggles
  • Rubber gloves
  • Safety rope
  • Old clothes
  • Slip resistant shoes
  • Ladder

Safety

Working on a roof can be dangerous, and it becomes even more hazardous when wet, so be sure to take adequate safety precautions. Avoid working on steep roofs, wear slip resistant shoes, and use a safety rope where needed. When working with harsh chemicals, be sure to protect your skin and eyes.

Bleach can damage or kill other plants in addition to algae, so wet down any grass, shrubs, or other plants where runoff will occur before and after applying bleach. Covering bushes with plastic after wetting them down helps as well.

Cleaning

It’s best to clean your roof on a cloudy day to prevent the cleaner from evaporating too quickly. If you know the manufacturer of your shingles, contact them or check their website for specific recommendations on cleaning. When using a product made for cleaning roofs or oxygen bleach, follow the directions on the container.

While the recipe for cleaning a roof with bleach can vary, the basic formula is:

  • 1 quart bleach (6% sodium hypochlorite)
  • 1 gallon water
  • 1/4 cup TSP (trisodium phosphate) or other heavy duty cleaner (don’t use a cleaner that contains ammonia or is not recommended for mixing with bleach, as it can result in poisonous chlorine gas)

Pour the ingredients into a pump type garden sprayer, mix well, and spray.

After wetting down the roof with the solution, allow it to remain on the roof for about 15 minutes before rinsing off with a hose.

Prevention

To keep algae from coming back once your roof is clean, install a strip of copper or zinc coated sheet metal along each side of the roof just below the ridge. To be effective, 2”- 4” of metal should be visible on the roof.

While copper is more toxic to algae, galvanized sheet metal is much less expensive. Both copper and galvanized metal are available in rolls of various widths and thickness both online and from local metal suppliers. You can also purchase zinc strips specifically made to eliminate roof algae from Z-Stop.

Narrow strips of sheet metal can be attached directly to your roof using roofing nails or screws with a rubber washer. For wider pieces of sheet metal, loosen the self-sealing tabs on the top row of shingles with a putty knife, slip part of the sheet metal under them, and nail it in place under the shingles with roofing nails.

The methods used to eliminate and prevent algae on your roof can also be applied to moss.

Further Information



Please Leave a Comment

48 Comments on “How to Remove and Prevent Black Algae Stains on Asphalt Shingle Roofs”

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  1. vicki meister Says:
    August 2nd, 2008 at 10:14 am

    where do i buy some trisodium phosphate?

  2. Dot Moran Says:
    August 13th, 2008 at 10:42 pm

    There is a large pond on another persons property across the road from our house. Since these algae spores are air borne, could that contribute to the discoloration on our roof?

  3. Omprakash De Says:
    September 10th, 2008 at 11:52 am

    What % of Zinc Oxide ,I have to add in a Cement bag to prevent gorworth of moss on side work.

    Thank You

  4. Terry Reed Says:
    September 20th, 2008 at 2:21 am

    Found a service called SHINGLE RENEW has a better recipe and tells where to buy cheap,safe chemicals.Informative how to on Cleaning asphalt shingles yourself…http://www.ShingleRenew.com

  5. Zan Says:
    August 17th, 2009 at 3:40 pm

    Thanks for the help. How long before you see an effect on the shingles with the TSP soulition.

    Thanks, Zan

  6. Official Comment:

    Ben Erickson Says:
    August 19th, 2009 at 11:27 am

    TSP is a strong cleaner (it’s available at home centers and paint stores), but since you aren’t scrubbing your roof with it, it mainly acts to reduce the surface tension and allow the bleach to soak in without running off the roof. It’s the bleach that actually kills the algae. The effect of the bleach should be visible right away, though it will become more pronounced once it has had time to dry. Oxygen bleach, on the other hand, can take several days to a week before the difference is very noticeable.

  7. sembatya habib Says:
    September 14th, 2009 at 6:15 am

    i want to clearly know how to remove and prevent algae, moss on clay roofing tiles; the procedure,the cleaner, and other tools so that we can start this project in uganda.

  8. Official Comment:

    Ben Erickson Says:
    September 14th, 2009 at 7:58 am

    Hi Sembatya,
    The above article on removing algae from a room can also be applied to removing moss. Additional information on removing moss can be found in our article How to Remove Moss from a Roof. Good luck with your project.

  9. rita Says:
    April 6th, 2010 at 5:24 am

    Please let me know how to remove green algae from tiles on the ground and on cement. thank you

  10. Official Comment:

    Ben Erickson Says:
    April 7th, 2010 at 10:58 am

    Hi Rita,
    Try spraying the algae with a mixture of 1 part bleach to 4 parts water with a little detergent added to break the surface tension. Make sure the detergent doesn’t contain ammonia and the directions say it’s okay to mix it with bleach. Mixing bleach with ammonia, or cleaners containing ammonia, can result in forming poisonous chlorine gas.

  11. Mark Trine Says:
    April 26th, 2010 at 11:32 am

    After putting down the zinc strips what adhesive or sealant should be used to cover nail heads and hold shingles to the zinc strips?

  12. Official Comment:

    Ben Erickson Says:
    April 27th, 2010 at 12:46 pm

    Hi Mark,
    If you buy a product like Z-Stop, mentioned in the article above, they include nails with a rubber washer on them to prevent leaks. You can also buy roofing nails with rubber washers on them that are used for metal roofing. If you use a wider strip of stock copper or galvanized sheet metal, slide a couple of inches of the metal under the shingle tabs and attach it with roofing nails beneath the tabs so they’re hidden (a dab of roofing cement on each one would be a good idea). Good luck with your project!

  13. Steve Rock Says:
    May 19th, 2010 at 6:52 pm

    While the article identifies TSP as trisodium phosphate, the photo shows a package of Red Devil TSP/90 Heavy Duty Cleaner which, based on Red Devil’s site, is actually sodium metasilicate, pentahydrate (ref: http://www.reddevil.com/pdfs/msds_0261_0265.pdf). Will this also work? Is it preferred over trisodium phosphate?

  14. Official Comment:

    Ben Erickson Says:
    May 20th, 2010 at 8:15 am

    Hi Steve,
    I don’t know if the TSP/90 cleaner pictured works better than trisodium phosphate or not, but it did do a good job of cleaning the algae stains off the roof we tested it on. Thanks for the feedback!

  15. Arly Sutroa Says:
    August 29th, 2010 at 4:13 pm

    If you use ferrous based nails for nailing zinc strips, the iron will oxidize the zinc in the strips and the strip will corrode and eventually detach from the roof. Hot dipped galvanized nails will slow down the process but eventually you will have to reinstall the zinc strips. A non-metallic or plastic/rubber coated metal fastener would be preferred to reduce the zinc corrosion

  16. Official Comment:

    Ben Erickson Says:
    August 31st, 2010 at 10:50 am

    Hi Arly,
    Good point, thanks for the tip!

  17. michael matulaitis Says:
    October 5th, 2010 at 2:15 pm

    Hi Danny,
    Do you know of a product that I can spray on my roof shingles so that the little stones won’t wash away?
    I did not have a ridge vent, and my roof is failing on on the south side. I am going to re-roof the south side and
    install a ridge vent. I would like to protect the other side from further erosion of the aggregate.
    Mike

  18. Ralph Says:
    November 10th, 2010 at 11:40 am

    I have run into what looks like black roof algae on a fiberglass deck below a kynar-painted metal roof (the roof is OK) in a coastal North Carolina environment. It cleans up readily, but comes back in 6 to 8 weeks. This is the first time I have run into this problem. Have you run into this before? If there is a cleaner with residual algea resistance, it would be interesting. I’m guessing that the other choice is to paint the deck with an algae resistent paint.

    Thanks,

    Ralph

  19. Carolina Allison Says:
    November 22nd, 2010 at 11:52 pm

    What do I need to remove algie from cement? Is there anything I can do to prevent it from comming back? How do I remove it from wood, privacy fence?
    Thank you for your help!

  20. Official Comment:

    Ben Erickson Says:
    November 30th, 2010 at 9:14 am

    Hi Carolina,
    The same methods used to clean the roof in the article above can be used to clean your cement and fence, or you could use a pressure washer to remove it. Good luck with your project!

  21. Bob East Says:
    January 28th, 2011 at 12:38 pm

    I think the use of bleach is not only hazardous but it’s environmentally friendly. The bleach and TSP will wash into the surrounding ground and on it’s way can damage gutters and vegetation. I prefer the use of a product called Spray & Forget which you spray on the roof or any surface contaminated with algae or moss and it does a great job. It isn’t instantaneous like bleach and can take months but it’s the safest way to eliminate the problem

  22. Marv Says:
    March 10th, 2011 at 2:47 am

    After discovering that I had this “stuff” on my roof last summer, I spent a dozen or so hours doing internet research to find what to do about it : First , I did ~ 25% of my Garage roof – THE WORST AREA ! – using the homemade brews described, followed by a modified pressure washer WASH using VERY LOW PRESSURE and a SPREADER WAND to keep from concentrating the stream in small areas : a 20′ x 30′ area took several hours to to do the actual cleaning ( the tool , equipment & supply mixing took just about the same time ! TOTAL TIME WAS A FULL HALF DAY !

    THEN , I wanted to use the COPPER or ZINC metal protection routine ; but found the COST WAS FAIRLY HIGH ! That was UNTIL I remembered that CONGRESS DEVALUED THE MOST BASIC PART OF OUR MONEY TO MAKE IT CHEAP TO PRODUCE !

    The American PENNY is a COPPER-COATED-ZINC-SLUG ! SO , I collected several dollars worth of PENNIES , I cleaned them with a QUICK soak in DILUTED BLEACH, and quickly rinsed them with a water bath ; then distributed them along the top row of shingles @ ~6″ spacing : SO FAR THIS IS CLEANING THE UNTREATED ROOF AREA FROM LAST YEARS EFFORT QUITE GOOD !

    ALSO , the ACTUAL COST WAS ~495-PENNIES : $4.95 !

    What WAS a pain was waddling along, placing them !

    My next development will PROBABLY be to expand the technique to using (drilled) PENNIES as “washers” on roofing nails ; even though the existing Pennies are still right where I placed them ( I have a rather shallow slopped roof) : Even though this is a rather LABOR INTENSIVE approach , the COST IS VERY CHEAP – compared to purchasing Zinc strips – which I ALSO now have !

    I will do another (back-side) roof area this year ; using PENNY-WASHERED-ROOFING-NAILS for tacking down the Zinc Strip(s) ; even though they come in 50-Foot Lengths , it is NOT a good Idea to put them down that way ; the Zinc is VERY SOFT , and will tear itself loose from the Nails due to Heat-expansion-contraction if NOT cut to 5′-10′ Lengths.

    ZINC PRODUCT : “MOSS BOSS” from Menards INTERNET SALES – NOT from their local store ! IT IS ~ 100%-PURE-ZINC ; NOT GALVANIZED CRAP METAL THAT WILL RUST & STAIN WHITE SHINGLES ! I verified their claim of Purity by MELTING a thin strip using SOLDERING equipment – it IS soft as Lead !

    If you want to try this Product , be PREPARED to deal with VERY SOFT METAL ! If you have problems working with Aluminum Foil, you may want to avoid this! IT IS THICKER & STRONGER THAN ALUMINUM FOIL ; just making a POINT !

    By Summer, this year, I hope to have a WHITE ROOF , again !
    (With small DOTS nailed inconspicuously near the ridge)
    ///MRB

  23. Official Comment:

    Ben Erickson Says:
    March 10th, 2011 at 7:33 am

    Hi Marv,
    Thanks for the tips on how to remove black algae stains from a roof!

  24. Bill Says:
    October 16th, 2011 at 4:27 pm

    A good efficient roof cleaning formula is 1 gal Chlorox, 1 gal water, 4 oz of dishwashing detergent (that doesn’t contain ammonia and is safe to mix with bleach) and 4 oz of sodium silicate (same as sodium metasilicate, often available in bags at auto parts stores sold as radiator flush). Mix the soap and water well first then add the bleach. This will cover 200 sq. ft. Spray the black stains first then the entire roof so the stains get a second dose. DON”T RINSE!!! The bleach degrades into salt which kills microbial growths and the sodium silicate does the same. They’ll get reactivated by high humidity, dew, fog or rain to eliminate more growth. A few hard rains will flush off the stains.
    The sodium silicate naturally adheres to the roofing and is slowly released to deter regrowth for awhile. Once stains redevelope and stay then it’s time to recoat the entire roof since this dark algae can develope anywhere upon it.
    This job goes much faster if you can borrow or rent a 12 volt diaphram garden sprayer with a large tank and a slew of hose (preferably on a reel) Be sure to wear rubber boots plus gloves and stay upwind while applying the solution.
    I’m a housepainter and have been using this formula and method for decades on customers’ homes. It works faster tha Spray & Forget at much less cost. S&F could be used as an preventative treatment after the stains been removed, tho I’d mix it with water in a tank before application, That’ll provide a more uniform coverage opposed to the inefficient hose-end sprayer that dispenses product in a scattered fashion so more product needs to be sprayed to get the desired results. (ie: 50 sq. ft. vs 100-150 sq. ft. when premixed)
    I wouldn’t bother with metal strips. You’d be better off dissolving copper sulfate in water then applying that to the roof to deter any growth. You could use that instead of bleach/soap for stain removal. Costs much less and isn’t as nasty yet does take a bit longer for the rain to remove the crud. Use 1 oz CS and 4 oz Ivory Liquid per gallon and treat the roof as stated above. The crud will turn brown and get washed off by rain as it decays into dirt. The copper also will deter regrowth for awhile, too. Copper isn’t dangerous to use. It’s a needed nutrient for plants and animals. Our bodies naturally slough off any excess copper we consume in foods or random contact while plants welcome it since the mineral is usually in short supply from dirt. I also treat customers’ roof with copper sulfate for cleaning and stain prevention since it works great. Haven’t done mny in the past few years due to our Texas drought. All this funky stuff needs moisture to develope and grow. We’ve been so dry little developes and what does get’s whiped out by the sun’s UV rays. Even existing nasty stains on homes have nearly disappeared. The sun turns them to dust and our rare rainfalls washes off the debris. Then it stays dry as a bone to deny any regrowth. There are some “professional” roof cleaners in drought stricken areas that started claiming their straight bleach treatments will keep a roof clean for 5 years gauranteed. Boy howdy will they be in for a surprise when humidity levels and annual rainfalls return to normal! Now if you have a steep pitched roof then I’d use one of them since they’re equiped and insured. Their product (an old painter’s trick) does work quite well plus gives immeadiate results that consumers rather have instead of waiting awhile. Just be ready for them to hem and haw around when you make a warranty claim since they’ll be dealing with a slew of those.

  25. Official Comment:

    Ben Erickson Says:
    October 16th, 2011 at 7:39 pm

    Hi Bill,
    Thanks for the helpful tips and feedback on cleaning your roof!

  26. Bill Says:
    October 16th, 2011 at 9:12 pm

    Hiya Ben,
    It’s not rocket science if one does their homework a for the cause, the common materials used to get rid of the crud and practical methods to get rid of them. My rain-rinse methods save customers the cost of rinsing and me the liability of possibly washing off granules (which naturaly come off due to weathering).
    I mostly deal with dark Algae (Gloeocaspa Magma) here in the south. It thrives on the calcium carbonate that’s steadily extracted from the granules by mildly acidic rainfall. New roofs take awhile before enough comes out to support GM growth. Once it starts coming out GM will be a constant problem, Using products that will deter their growth helps delay future treatments, GM is the same crud that turns concrete (and composite decking) black so keeping these surfaces clean of te crud too, will help prevent it’s spread back onto your and neighbors’ surfaces. This is why neighbors should act in conjunction in having these surfaces cleaned since it reduces the amount of GM spores to be broadcasted across neighborhoods.
    Perhaps these DIY’s that frequent this site could encourage neighbors to do the same on a given weekend? They could chip in on a sprayer rental to reduce costs plus lend a hand. It’s always wise to have a “groundman” present when a worker is on the roof in case something happens.
    Heck, if you drain and flush your vhicles’ cooling system then you can use the old antifreeze and flush on your flat concrete! Just add a few gallons of bleach, douse the cement and rinse away 30 minutes later. It’ll put the whammy to the crud and allow easy removal with a hose or pressure washer. Once done and dru then treat the surfaces with copper sulfate to deter regrowth. These surfaces can be retreated with copper every two years to deter regrowth, Can do that when retreating the roof.

  27. Tom from Cobb Says:
    November 15th, 2011 at 11:58 am

    I have very bad stains on my roof and have tried the bleach + TSP mixture as well as Spray and forget. ( The Spray and forget was used first with no results then tried the bleach / TSP mixture ) I have done this exact to the instructions given and the stains are still there. My roof is steep and difficult to walk on. ( I think it’s a 10/12 pitch ) Could it be these solutions are just running off to quickly and not having time to soak in or did I wait to long to address this. These stains have been on the roof for aprox. 5 years.

    Thanks for any recommendations

  28. Gary Says:
    November 20th, 2011 at 6:30 pm

    After researching different opinions on the matter, I tried what the shingle manufacturers (all of them) suggest. Something like 50 50 bleach/ water with some tsp. Not much help!
    So, today I used a 10% bleach/water and a little dishwashing detergent, then pressure washed it. Fantastic results!
    Granted these 10 year old strip shingles (designed to last 20 years) did lose their adhesion to one another but I know after one sunny day, they will reseal.
    I went back over it again with the bleach solution and left it, for good measure.
    As we all know bleach will kill mildew.
    I have been a residential builder for 30 years.
    I am looking into installing some zink strips. I am worried that any metal fasteners will cause corrosion. The rubber washered nails are designed to be used with some corrugated roofing and they work well there to seal out water. They will do nothing in respect to sealing out water on a shingle roof. The rubber may create a barrier between the bottom of the head of the nail, but what about the shank?
    Any fasteners/protrusions left uncovered are chanceing leakage.
    I am luckey enough to have a very walkable roof, so was not too difficult.
    Good luck all.

  29. Official Comment:

    Ben Erickson Says:
    November 20th, 2011 at 9:38 pm

    Hi Gary,
    Thanks for the feedback on your roof!

  30. Doug Says:
    April 22nd, 2012 at 2:14 pm

    A great roof cleaning product for removing black algae stains and moss on you roof is Roof Resolve.

  31. Heather Stiles Says:
    April 26th, 2012 at 5:07 pm

    I have about 1000 square foot of composition roofing that I need to get the moss off from. I’d like to make and use oxygen bleach. Can you help with the ratio of baking soda, hydrogen peroxide and water in large quantities?

  32. Bill Says:
    April 26th, 2012 at 9:33 pm

    Heather,
    Here’s something easier to mix, is less expensive plus provides enough to retreat the roof once. Get 2 lbs of copper sulfate root killer and some regular Ivory Liquid dishwashing detergent. Dissolve the copper in a plastic gallon milk jug with water. You’ll be combining 1 oz. of that with 20 oz. of water (6.5 oz. per gallon of water) Add 2 oz. of Ivory Liquid per gallon and mix well. Apply 1 gallon per 100 sq. ft. to the entire roof then give the moss another dose once the first application dried. The moss will die off and turn brown. Let it decay away naturally for awhile before trying to sweep it off or just let the wind and rain remove it over time.
    The copper applied above the growths will leach out to inhibit moss growth for 1-2 years or more. You’ll have enough copper solution left over to retreat the the roof once the moss starts redeveloping.
    Copper runoff does nothing to plants below except make them healthier since it’s an essential mineral they require just like humans. Miracle-Grow contains copper along with Centrum Silver. It’s not harmfull unless applied or consumed in gross amounts. The soap serves as a nuetral wetting agent/spreader/sticker which enables the solution to soak into the roofing granules, spread out as an uniform film on the moss and stay there instead of running off. Since it is a detergent it’ll get reactivated by rain to help loosen and suspend any dirt/crud so the rainfall can rinse that off the roofing.
    Now if you live where cleaning off mildew from exterior surfaces is a constant chore the just hit the moss with the same bleach solution. That’ll kill it off but won’t inhibit regrowth so just rewet the roof with the bleach solution whenever cleaning off the rest of the place. That’ll help keep it in check without fooling around with two seperate solutions.

    Hope this helps!
    Bill
    East Texas

  33. Bill Says:
    April 27th, 2012 at 12:06 am

    ARMA (American Roofing Manufactureres Association) provides effective recipes for dealing with biological crud on roofing. Those use powdered clothes detergent but work better if you substitute a powdered coolant system cleaner that contains sodium silicate and borax since those will deter regrowth for awhile. Just wet the roof down with the solutions then give the growths/stains a second application. Don’t bother rinsing since future dew and rain will reactivate the sodium silicate and borax to kill off remaining growths. Heavy rains will wash the growths and stains away. When the roof starts redeveloping stains or growths then that’s time to hit the roof again. You can retreat the entire roof or just the sections prone to the cruds’ developement.
    Now let’s discuss granule loss from shingles. Moss and lichens have hyphae that will dislodge granules. The black algae doesn’t and simply adheres to those and each other so actually can prevent granule loss if their colonies become dense. Once those are dissolved with cleaning agents and rinsed away with any sort of pressurized water will remove any granules that naturally lost their bond due to weathering to the asphalt base and wind up in the gutter or on the ground. That’s why I prefer to let the rain rinse the roof instead of blasting the surfaces with a pressure washer or even a strong stream from a garden hose since it keeps me out of trouble. If hard rains do remove an excessive amount of granules along with the stains then the shingle may be defective or suffered hail damage during the storm or from those in the past that initially loosened the granules. Adjusters know it can take 2-3 years for hail damage to become appearant so usually honor the claim. Most don’t mind if you periodically spray the roof with bleach to control unwanted growths. On the otherhand there are adjusters who are complete jerks that try to deny claims for any reason. Our area had “roof cleaners” that went out of business by being sued by customers whose claims were denied because they had the roof cleaned previously using pressurized water for a rinse, which the adjusters’ claimed was the reason for the granule loss. The same adjusters then OK’ed claims where the homeowners just sprayed a bleach or copper solution on and left it since it’s been a common practice for decades if not centuries without ill effects to the roofing surfaces. They can’t argue about doing that either if you use the ARMA recipe or a product sold for that purpose such as Bayer Advance 2 in 1 Moss and Algae Killer sold at the big box stores. (it’s a RTU product with it’s own hose end sprayer which makes it easy to apply yet inefficiently. You’ll get better results busting off the sprayer and mixing the contents with 4 gallons of water in a bucket then applying that @ 1 gal per 100 sq. ft instead. One bottle costs around $15.00. At that price you can buy some coolant cleaner plus 3 gallons of Chlorox which will make 7-10 gallons that’ll treat 700-1000 sq ft. instead with a residual effect to deter regrowth. Bayer’s product doesn’t offer that either)
    If you’re dead-set on using oxygen bleach then your best bet is sodium perborate. It’s made with borax which is a natural biocide. When applied and left it leaves a film of borax that’s reactivated by moisture to continue eliminating unwanted biological growths. It just needs to be dissolved in hot water to fully dissolve into solution compared to the less effective sodium percarbonate. You can add Ivory Liquid to enhance it’s effectiveness. The stuff can be bought in bulk at reasonable cost (sacks or buckets) at Univar, Rodgers & Van Waters and other chemical supply houses. Get your friends and neighbors to chip in since it also works great on wood fences, decks and concrete/masonry surfaces. Those can be treated the same way as roofs if you want to save labor and water by avoiding rinsing. You also can add some anti-freeze to the mix to retard evaporation plus give it additional antimicrobial properties. It’s safe to use as long one takes the typical precautions when applying any sort of cleaner or pesticide.
    Hope this helps some of you folks out. There’s no need to buy expensive products being hyped when one can make something better for less from products readily available on store shelves. The trick is to get rid of whatever’s present with minimal effort then keep it from redeveloping with periodic retreatments before it get’s established again. Doing this inexpensively is an added bonus!

  34. Official Comment:

    Ben Erickson Says:
    April 27th, 2012 at 8:09 am

    Hi Bill,
    Thanks for all the helpful info on removing black roof stains!

  35. Sam Says:
    May 6th, 2012 at 9:08 am

    We used a roof cleaning service called Roof Shampoo. It was like getting a new roof. The products are all eco-friendly and don’t contain bleach, so we didn’t have to worry about killing our flowers or bushes. And they used a very low pressure rinse. The contractor put his hand directly under the water spray to prove the pressure was so low. I was truly amazed at how well the cleaning worked. I’m telling you, our roof looks brand new. We didn’t have to wait for rain or anything like that. When they finished the cleaning, all the stains were completely gone. We were glad we made the decision to hire them. We researched how to get rid of our ugly roof stains for months before we decided which way to go. There are so many different ideas on this subject. Well, roof shampoo worked for us. After we had it done, my sister who lives in Ohio had hers cleaned by roof shampoo too. She was really happy with the results and her neighbor is going to do it too. The services are available in a lot of states.

  36. Roof Cleaning Reading Pa Says:
    May 21st, 2012 at 4:27 pm

    I am a professional Roof Cleaner business owner of Colonial Power Washing and Painting in Reading Pa who uses safe methods of roof cleaning. Never is there a time to use a Power Washer on a shingle as it will remove the granules. The safest chems to use is Chlorine although it has to be mixed in a certain ratio to water with an added surfactant.

    As far as “Safe products for the environment that will not harm landscaping” My question is how will it kill the algae on the roof, but not the vegitation surrounding it? That makes no sense in my opinion. Everyone gets so hyped up on the environmental thing with chlorine yet:

    We add it to our pools and allow our children and grandbabies to swimin it. We add it to water for purification reasons when needed when power is down and drink it. We swim in the Ocean which is salt. Secret:Chlorine and bleach break down to salt eventually…

    We pre wet all of our landscaping and even cover if need be if there are no gutters present. We also bag all of our down spouts before we apply our Detergents. We then apply our Roof Revolution(TM) to the entire shingles using specially calibrated low pressure pumps while still watering down the surroundings as well as after the spraying of our shingle cleaner is applied.

    The results are always a like new looking roof which we give a 5 year warranty on staying clean, but more often than not it stays cleaner longer than that.

    Itsnot rocket science, but it takes much in field work experience to master it and it is not for the casual weekend warrior as we also wear safety gear and osha approved breathing masks.

    Borax and TSP have been used in the past by guys who have been cleaning roofs for over 30 years and are leaders in the industry. The problem with TSP is is gunks up your pumps and also will etch your window glass and exterior paint job if you donot take care. Borax is a biostat that willkeep the bugs away as people in the pest control service will tell ya.

  37. T Michael Says:
    July 30th, 2012 at 11:33 am

    How to clean black and green alge and lichen from a low sloping asphalt roof?

  38. Dan Cronauer Says:
    November 28th, 2012 at 1:56 pm

    The only way to clean a roof is using non pressure soft-wash. I work cleaning roofs. This method works the best and will not cause any damage to the roof surface. As mentioned above TSP can etch glass, and isn’t need during the process.

  39. Lee Says:
    November 28th, 2012 at 3:00 pm

    Dan, do you use a cleaning product with the soft-wash?

  40. Grant Says:
    April 22nd, 2013 at 4:05 pm

    alright…I have a couple of questions! 1. I need a recipe that will clean a roof and not harm the plants and house as Im applying it.
    2. If it is best to use a bleach on a roof how much watering is needed to keep from killing plants and streaking the houses paint?
    3. I need to know what is the best practice to get instant results.
    4. If you can please give me the directions to how to make your recipe (like you were telling a 5 year old) haha

    thanks everyone

  41. Kirk Warner Says:
    August 27th, 2013 at 2:20 pm

    Simple cover your plants just as painters do. Using bleach is recommended by most shingle roof manufactures and the ARMA, (Asphalt Roofing Manufactures Association).

    ARMA statement:
    “The most effective method of cleaning algae and moss from a roof is w ith a 50:50 mix of laundry strength liquid chlorine bleach and w ater. Apply with a sprayer and allow the solution to dwell on the roof surface for 15 to 20 minutes, and then rinse thoroughly with low pressure water”.

  42. Phoebe Monroe Says:
    April 29th, 2014 at 6:51 am

    Thanks to everyone for their wonderful comments, suggestions and tips. This has to be the best website out there for roof stains.

    After reading all the comments I now understand why my approach didn’t work.

    Not sure which suggestion I will try next but I am sure I will have the prettiest roof in the neighborhood once finished!

    Thanks again,
    Phoebe

  43. Sophia Liam Says:
    May 22nd, 2014 at 7:40 pm

    I didn’t realize those stains were algae! Cleaning the roof makes so much more sense now. I do have one question. How do you know if the cleaner is able to be mixed with bleach? Will it always say so on the label or do you have to do some online digging?

    Thanks,
    Sophia Liam

  44. Anthony Hopcraft Says:
    June 21st, 2014 at 7:18 am

    I have been using nano titanium dioxide on roofs and they never get moldy because of the photo catalytic activity. Roofs stay cleaner longer

  45. Mark Friedmont Says:
    June 23rd, 2014 at 3:48 pm

    We had Roof Shampoo clean our roof too and it looks like brand new. I made sure I checked the amount of granules in the gutter before and after and it was very little. That was a major concern for me. They told us that they use very low pressure, but at high volume to rinse the roof. He also explained that the reason their product kills the algae on the roof and not my plants was because plants have a “cuticle” surrounding them while algae does not. Whatever, my roof looks great!

  46. Bruce Sullivan Says:
    June 29th, 2014 at 6:39 am

    There are many marketing efforts about roof cleaning. No wonder the home owner becomes confused. That said. The most effective and long lasting process, in most cases, involves the use of sodium hypochlorite (pool chlorine)as the lead ingredient.

    Sodium hypochlorite is used for household and laundry cleaning, sanitation, deodorizing and disinfection, municipal water, sewage and swimming pool disinfection, medical environment disinfection, disinfection purposes in food industry and food manipulation, textile industry and pulp and paper bleaching, chemical synthesis, as a multisite fungicide in agriculture and horticulture.

    Given such, it isn’t the use of that which should be of concern, but the person using it. That is why hiring a roof cleaning expert is the best route to go.

    Yes, you can hire some franchise that boost eco-friendly cleaning solution and then they get up on your roof with a pressure machine because the solution they are using won’t properly clean the roof, they need pressure to remove it. Why anyone has to get on a roof and then run some machine/pressure over it is beyond me. Not to speak of the potential liability involved from such a process.

    With the proper ratio of cleaning solution, lightly sprayed upon the roof, let dwell for short period of time and then rinse with garden hose pressure will do the job. Which is all done from a ladder, not getting on the roof. The roof will stay clean for 6 to 8 years subjectively. Plus the cost of such a service is about 10% of the roof replacement cost on average.

    We have never had an issue with landscaping cleaning this way. Nor has it had any adverse effect on the environment, like you going to start your car does.

    For those that claim the use of “very low pressure” beware, if they have anything other than a garden hose in their hand to rinse they are using pressure!

  47. scott schoppert Says:
    July 1st, 2014 at 9:18 pm

    IF YOU ARE GOING TO REROOF YOUR HOUSE SOON USE ATLAS PINNACLE WITH SCOTCHCARD PROTECTION ON IT, IT WILL KEEP ALGE FROM GROWING FOR THE LIFE OF THE ROOF. YOU MUST USE THER PROCUT HIP AND RIDGE SHINGLES TO GET THAT LIFETIME PROTECTION.

  48. Hugh Kim Says:
    November 11th, 2014 at 10:47 am

    You may have not had an issue with killing landscaping, I did! Last spring I was bamboozled into having a pressure washer clean my roof with the no pressure sodium hypochlorite tsp method. I got the same smooth talking, very convincing verbiage from him as Bruce Sullivan just wrote. My results…….. $7300 damage to my landscaping and $800 replacement cost to my corroded and piitted nickel hardware on my entry and sliding doors. Lesson learned…….if you decide to use bleach, use the method listed in this article and do it yourself. Don’t pay someone $450 to splash $25 worth of bleach on your roof like I did.

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