Roof Algae Cleaning Myths Debunked

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There’s a lot of false information about roof algae cleaning floating around right now, and I guess this is to be expected because it’s still a relatively new industry and most homeowners still aren’t that familiar with it.  But I’m tired of seeing all the confusion and decided that it’s time to set the record straight.  It’s time to blast some common roof cleaning myths out of the water once and for all.  So, without further ado, I give you the top ten myths about roof stain removal.

Myth #1:  Black roof stains are caused by tar, acid, dirt, or jet fuel. Roof stains are caused by a hardy type of blue-green algae called Gloeocapsa Magma.  All it takes is for one algae spore to land on your shingles and take hold and then it’s off to the races.  The algae will continue to multiply and spread, its growth fed by the limestone filler in the shingles and moisture.

Myth #2:  Algae on roof shingles is really a signal that it’s time for a new roof. Simply the presence of algae stains does not necessarily equate with needing a new roof.  In many cases all a roof needs is a good professional cleaning to restore its original look and health.  You might notice that roofers don’t like roof cleaners very much, and this is because we keep them honest.  If a roofer tells you that you need a whole new roof just because of some algae staining tell him to take a walk and look up your local non-pressure roof cleaning company instead.  You’ll save a huge amount of money.

Roof Algae CleaningMyth #3:  Roof algae removal will have no real impact on a home’s curb appeal. Most people are shocked when they see how much better their home looks after a roof cleaning.  I think this is because most homeowners have gotten so used to seeing the stains on their roof that they’ve completely forgotten how good it once looked.  I’ve lost count of how many times I’ve cleaned the roof of a house that had been on the market for months with virtually no activity and within days of the cleaning it finally started getting serious offers.  I’ve said it before and I’ll say it again that no matter how beautiful your landscaping, no matter how clean your windows, no matter how precise the painted trim, if your roof is covered in filthy algae stains then it will still ruin your curb appeal, if not in your eyes then in the eyes of your family, friends, neighbors, and potential buyers.

Myth #4:  Roof algae is only a cosmetic issue so it can be ignored for now. If not cleaned off and kept at bay roof algae has the ability to shave years off the life of your shingles.  It’s important to remember that roof algae is a living organism that needs food to continue to grow.  Guess what the favorite food of roof algae is?  That’s right – your shingles!  Shingle makers now use limestone filler in the manufacturing process which the algae just loves to chew on.  This will result in premature loss of shingle granules and general deterioration.  Shingle granules are vital to the health of your roof and home because they work to deflect UV rays and heat away from your roof surface.  If they are gone or covered with algae then you will have a hotter attic and higher AC bills.  You’ll also have to replace the roof a lot sooner, and with the average new roof these days topping $10,000 it’s just a no-brainer to keep your shingles clean and functional for a fraction of the cost.

Myth #5:  The best way to go about removing roof algae is with high pressure. I’ve beaten this one to death on this site but it bears repeating that, next to positioning your home in the path of a tornado, power washing your roof to remove algae stains is the worst thing you could possibly do to it.  Just because your concrete, deck, and brick siding were pressure cleaned doesn’t mean you should do it to your shingles.  Don’t you have any idea how flimsy and fragile your shingles are?  Don’t you realize how many thousand or tens of thousands of shingle granules will pop right off with the use of a power washing wand?  It just always blows my mind that people think this is a good idea.  Yes, blasting your roof with 2000 PSI will remove some of the stains, but if it removes some of your actual roof in the process then what the heck is the point?  If you bought a roof algae remover and somewhere in the instructions it says that you should walk up on your roof with a power washing wand in hand and unleash hell on your shingles then it’s safe to say that you purchased the wrong product.

Myth #6:  Chemical roof cleaning will damage shingles, gutters, and landscaping. If you’re using the right chemicals with the proper procedures and rinsing techniques then you have nothing to fear.  I’ve cleaned hundreds of roofs with non-pressure chemical methods and have never once seen a situation where we caused damage to someone’s home.  I also only clean roofs with a helper present who’s sole responsibility is to rinse the heck out of the grass, bushes, and perimeter landscaping so that there’s absolutely no chance of plant damage.  We usually do such a good job of rinsing that homeowners notice that their landscaping actually looks especially healthy and vibrant in the days following the cleaning.  ARMA (the Asphalt Roofing Manufacturers Association) and GAF (North America’s largest shingle maker) both recommend that shingles be cleaned with non-pressure, chemical methods, and any home inspector worth his salt would also concur.

Myth #7:  It’s only necessary to clean the sections of the roof that have visible stains. Just because you can’t see algae stains on certain parts of the roof doesn’t mean that it’s not already there and beginning to develop.  Keep in mind that in its early stages roof algae is completely invisible to the naked eye.  It’s not until the more advanced stages that it actually turns black and becomes visible.  So if you can see algae on even one section of your roof that means that it’s probably already taking hold on your entire roof.  I always try to explain this to my customers but occasionally I still get people who don’t believe it and demand that I only do a spot-clean to remove visible stains.  I reluctantly oblige their demands but am never surprised when I drive by a year later to see the untreated areas now completely covered in black algae!  Then they usually call me back with the standard, “You were right.  Can you please come back and clean the whole roof as you originally recommended?”

Myth #8:  Ambient temperature has no effect on the effectiveness of a roof algae cleaner. If you’re using the correct chemical mixture then it will be most effective when the temperature is above 50 degrees.  Below 50 and the power of the solution drops off rapidly.  If you absolutely must have the roof cleaned on a day when it’s right around 50 or a little bit lower just keep in mind that the chemicals will need to sit for a little bit longer on the roof to be effective.  So instead of giving it five minutes to kill the algae give it 15.  Then reapply if necessary.  On the flip side, if it’s an extremely hot day you may find that your chemical is
evaporating before it even has a chance to kill the algae.  In this situation you can simply soak the roof with water to cool it down before applying the chemicals.

Myth #9:  Roof cleaning is an easy DIY project that any homeowner can do in an afternoon. There’s nothing easy or quick about roof cleaning.  In fact, if you approach it with a cavalier attitude you run a good chance of injuring yourself.  If you want to have any chance of cleaning your roof safely and effectively then you need to set out a clear plan of attack, have safety procedures in place, and, above all, take your time.  Rushing through a roof cleaning only leads to trouble.  Unless you’re one of these guys that absolutely has to do every home improvement job on his own I would highly recommend that you just find a qualified, non-pressure roof cleaning company in your area.  Either you can hire somebody who has the equipment and experience to clean your roof in a few hours or you can spend an entire weekend doing it yourself and risking your life.  Your choice.

Myth #10:  Roof cleaning companies tend to overprice their work and take advantage of consumers. I guess I’m always a little disappointed when I tell someone that it will cost $300-$500 to clean their roof and they give me attitude and insinuate that I’m somehow ripping them off.  I think people hear that word “cleaning” and they think it should be cheap like carpet cleaning or house cleaning.  Think about it.  Does a carpet cleaner spend three hours at your house sweating his butt off and getting sunburned?  No.  Does a carpet cleaner run the possibility of paralysis or death by simply doing his job?  No.  Does a carpet cleaner spend $100 on chemicals for every single job?  No.  Can a carpet cleaner offer you a guarantee that the treated surface will stay clean for years to come?  No.  There’s so much more that goes into a professional roof cleaning than for any other kind of residential cleaning service that it’s really not even fair to lump them into the same category.  As a matter of fact, I actually think that most roof cleaning companies come in too low with their prices when you consider all the variables involved.  I also challenge you to name me one other home improvement service that can instantly transform a home’s curb appeal in a single afternoon for under $500.  Can’t be done.  And when you consider that it not only makes your home more beautiful but also extends the life of your expensive roof by a matter of years I think that having a roof cleaned is one of the smartest and most cost-effective things that a homeowner could possibly do to protect their biggest investment.

So now that I’ve cleared the air and educated you about the myths that surround the roof cleaning industry I hope you’ll take these words of advice to heart because they represent the straightest talk about this topic that you’re going to find.  I’m not here to serve up a load of BS just because I’m trying to sell a product.  I’m telling you like it is because there are too many lies flying around.  Either you can buy into one of the myths and be disappointed with the results or you can clean your shingles the right way and be satisfied with your new-looking, beautiful home that is free of roof algae.

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13 Responses to Roof Algae Cleaning Myths Debunked

  1. Excellent roof cleaning information, very well written!
    I posted this on my roof cleaning Blog, along with a link back to you!

  2. Min says:

    I think your information is very informative and I read it really carefully but what I didn’t find out was – what effect does algae have on a flat roof that is made with concrete. I don’t have shingles.
    I do have leaking problems and I don’t know if that can be solved with just a cleaning.
    Any help would be appreciated.

  3. admin says:

    Min- If there is leaking involved then I would get that solved first, and then you can worry about cleaning. Algae on flat concrete is probably more of an aesthetic problem than anything else but it is still worth contacting a local professional to get his or her expert opinion. Thanks for the comment.

  4. Lisa says:

    Great article, thanks. I can’t seem to find anyone in my area that does “roof cleaning”.
    Also, how do you prevent the problem from returning? Have you ever heard of roof-be-clean? If so, your thoughts? After reading about the product on their website, it seems like it could be a good solution to preventing moss/algae growth.

    • Zach Maynard says:

      In general any of those roof cleaning products don’t work Lisa. If it sounds too good to be true it generally is. If you still can’t find a roof cleaning contractor in your area, let us know and we can try to assist you.

  5. Paul Morgan says:

    It is an easy DIY job with a water hose and bleach/water mixture. I’ve done it for my house and it worked fine. It cost me about $12 in bleach. Use the outdoor bleach.

  6. brenda says:

    I live in the Charleston South Carolina area and have been unable to find someone to clean my algae stained roof. Two-years ago I hired someone with a pressure washing business with his assurances that he would use chemicals and a low pressure “witch.” Needless to say, the gutters and perimeter of my house were covered in granules…buckets full! And now the north side of my roof is stained again. Not in streaks, but in big patches. I am a single woman unwilling to climb up on the roof. But my house is a single story, simple roofline, sort of “l” shaped 1500 square foot house. I would consider spraying from atop a ladder. Although your site has lots of info I have been unable to find the actual recipe and technique for roof cleaning. Am I missing something on your site?

    • Zach Maynard says:

      Where are you from Brenda?
      The “witch” that was used on your roof is still a high pressure tool, and obviously did what it does. Which is clean your roof and take half the granules along with it.

  7. Ken says:

    Can you point us to some independent research that algae shorten the life of a roof, as discussed under Myth #4 above? And also to some independent data on the magnitude of this effect – do algae reduce roof life on average by 50%? 1%? or what? Obviously there will be considerable variation, but it matters whether the effect is major or trivial.

    ~ Thanks!
    ~ Ken

    • Zach Maynard says:

      Thanks for your question Ken, please check back frequently. There will soon be an article released that will cover your question!

  8. Marc Kunze says:

    Very informative information about roof cleaning. It definitely is another one of those household projects that will prolong the life of your home. It is also very much worth hiring a professional.

    Thanks!

  9. Laura Bezdan says:

    Dear Zach -
    Thank you so much for providing this resource. I like your writing style and greatly appreciate your content. This was a very good overview – concise information – exactly what I needed to know. You presented this information in such a way that I feel confident in your credibility.
    Thank you -
    LB

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