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How To Clean Algae From Roof

How To Remove Roof Algae

How to Clean Roof Algae


Clean roof shingles with Stain Solver. This roof is covered with different species of roof algae. You can see where the lead is helping to keep the roof clean. If there was a copper strip along the entire roof ridge, the roof would be perfectly clean. or THE IMAGE to purchase the copper strips and solid copper nails.

DEAR TIM: Many of the roofs in my neighborhood are covered with black streaks, mine included. What’s causing this to happen and can the roofs be cleaned? I’m able to walk on my asphalt shingle roof with ease, but am afraid of hurting the shingles by cleaning them. Once the roof is clean, is there a way to prevent the streaking from returning? Could all of this been prevented? Molly G., Jacksonville, FL

DEAR MOLLY: Hundreds of thousands of roofs on homes and other buildings suffer from the stains you’re plagued with. It’s a harmless algae that’s gorging itself on the powdered limestone filler that’s often added to the liquid asphalt in shingles to help add weight to them.

This limestone never used to be a component of shingles. When the matts used to build shingles switched from traditional felt paper to fiberglass, the manufacturers had a problem getting the shingles up to the minimum weight requirement. Someone decided to use powdered limestone dust, but they didn’t realize that it was a delectable food for the tiny algae. Fortunately, the algae doesn’t harm the shingles.

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Should You Remove Moss

When you get a roof replacement, you may want to have your roofers install the new roof over top of the old. In certain circumstances, this can help you save money. However, if your old roof has moss growth, can you still use this method?

You may need to deal with the moss before the full roof replacement. Your roofers will need to remove all the shingles on your old roof, or they may need to remove the largest chunks of moss with a pressure washer and then apply the new roof. It is only advisable to use a pressure washer because you no longer need to worry about the condition of the old roof. The new one will offer the protection your home needs.

How To Use Bleach Mixtures On Your Roof

The following procedure is for bleach-cleaning only using JOMAX. If JOMAXis not available in your area, use a TSP mixture with bleach added.

  • Bleach mixtures can injure sensitive plants. Because it is difficult to totally protect them from the mix, spray them down with clean water before applying the mix and immediately after, whether you cover them or not!
  • Using a plastic pump-type garden sprayer, thoroughly soak the affected area with your choice of chemical. Allow it to sit for at least 5 minutes.
  • Wash off all dirt and fungus residue. NOTE: Though powerwashing was recommended for years, the industry has moved towards low-pressurecleaning due to evidence of permanent asphalt shingle damage caused by high-pressure powerwashing.
  • Allow the roof to dry thoroughly. Inspect the roof for any remaining fungus… if it isslimy, or any sort of residue comes off on your hand, repeat the above steps. You must let the roof dry before a second application of mix. A second application of cleaner will not have its full effect on a damp surface!
  • If you think it wise to leave the bleach-brew on the roof longer than therecommended time, thinkagain! As mentioned earlier, long term exposure to bleach can damage most any surface, and yourroof is no exception. However, this piecemeal approach is the likelyto cause the least damage.

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    Another Less Common Occurrence Is Moss

    If you see green fuzzy stuff on your roof it is most likely moss. Moss loves cool, damp environments. If you have moss on your roof it will be commonly found on the North slopes in addition to overhanging treses or overhanging sections of the roof causing shade and allowing moisture to hang around and the moss to grow.

    Moss spores can become airborne and make their way onto roofs via wind, birds, squirrels, and other small animals, in the same way that algae makes its way to your roof.

    Once the moss spores land on a roof, they will gather in the spaces between shingles and eventually grow into thick spongy moss.

    Algae is a term for a large group of photosynthetic eukaryotic organisms. They are typically aquatic and lack the roots, stems, and leaves of other plants, though they still contain chlorophyllthe green pigments found in most plants. However, they are not plants but rather organisms also spread by spores, much like moss.

    Mold is the result of algae left too long on a roof. Algae needs perpetual moisture to exist, so they grow best in humid areas. When algae keeps the roof damp for long enough, rot can set in, commonly leading to mold growing and spreading.

    Should You Hire A Professional

    Roof Cleaning

    The answer depends on you. Maybe you cant get up on your roof anymore to clean it. Or you dont have any time.

    Well, if youre facing any problem, a professional roof cleaning service is your next best choice.

    Luckily, theres a ton of roof cleaning services today. You wont have a difficult time looking for them. But, the only thing youll need to watch out for is their price. They dont come cheap!

    Sure theyre using the standard bleach and water, but youre also paying them for their services! Well, thats the trade-off. You wont tire yourself, but youll need to spend some bucks to clean your roof.

    Nevertheless, always pick someone reliable. Reputable cleaning roof services are everywhere. Ask your friends and family they might have someone to recommend.

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    What Are The Dark Streaks On My Roof

    You may have noticed dark streaks across your roof. Given that moss grows upright on surfaces, and algae stays low and flush to the surfaces it grows on, its likely any dark streaks you see are algae.

    Algae staining on roofs all start out being spread by wind, birds, and varmints, affecting homes across much of the United States.

    This algae normally begins its lifecycle as airborne spores that will settle on your roof, especially those roofs that have asphalt shingles. The northern exposure of roofs has the most chance for algae to survive/thrive because that part of the roof is exposed to the least UV and dries last after morning dew and rain.

    As the algae grows and spreads, it begins to look like large black streaks on your shingles.

    How To Clean Tile Roof With Bleach

  • Add ½ cup gallon of water into the bleach
  • Mix the solution in a garden sprayer
  • Use a ladder to climb the roof
  • Inspect the areas with algae, moss, mildew, and the likes.
  • Spray the solution in the garden sprayer on your tile roof.
  • Wait for about 20 minutes.
  • Spray again until the algae is completely removed.
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    Clean & Prevent Black Algae Or Green Algae Stains On Roofs

    • about roof algae stains and black marks on asphalt roof shingles: causes, effects on roof life, cure & prevention

    InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

    Roof algae stains:

    Algae and occasionally fungal growth discolors roof shingles.

    This article explains methods for cleaning off and preventing future roof stains due to algae or “black fungal growth” or green algae on roof shingles, the effects of these conditions, and how to cure or prevent them.

    We discuss algae and occasionally fungal growth that discolors roof shingles. How to identify & prevent black algae growth and stains on roof surfaces. Advice about roof cleaning methods: chemicals, brushes, washing, power-washing roofs.

    We provide a list of type of stains and colors that appear on roof shingles and on other roofing materials.

    We also provide an ARTICLE INDEX for this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

    Choose The Right Day And Prepare The Area

    Removing Algae Stains From Roof Shingles

    Check the weather forecast and choose a cool or overcast day with little to no wind so the spray hits your shingles, not the neighbors. Those conditions allow the cleaning solution to soak deep into the algae colonies without evaporating too quickly.

    Next, repair any loose shingles or flashings, and clean the gutters and downspouts so they can drain freely.

    Then prepare the area by moving lawn furniture and covering vegetation, because youre going to have overspray. Even though the product we chose isnt toxic, the runoff can be pretty ugly. So a little prep work will save you cleanup time later.

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    A Brief History Of Algae

    Roofing manufacturers can provide shingles specifically made with an alternative type of mineral granule that resist algae growth. Earlier roofing manufacturers tried an algaecide coating to prevent algae growth. In the late 1980s manufacturers began using zinc granules but zinc was discontinued out of environmental concerns for using a heavy metal on roofs.

    Zinc can also emit a white rust that builds up as a white stain or oxide. By 1996 manufacturers were using several coatings on asphalt shingles to reduce algae growth, including cuprous oxide coated granules mixed in with other granules on the shingle surface. The percentage of copper-coated granules affects the resistance of the roof to algae.

    Is algae the same as mold on roof shingles? Kirbys 1996 article confused algae and fungal growth on roofs as equivalent, which may be ok since the same chemicals that resist algae growth may also resist fungal growth and stains. We discuss removing sooty black molds on buildings below. By the way, most of the roof surface samples we have tested have been shown to be algae, not fungal and not extractive bleeding stains.

    Shingle product names that include an AR suffix or 3M Algae Block are products manufactured and warranted to be algae-resistant .

    See CAUSES of ROOF STAINS and CATALOG of ALL ROOF STAINS for the causes and types of stains that occur on building roofs.

    Our complete list of types of black stains on building roofs is at CATALOG of BLACK STAINS on ROOFS

    Put Your Solution On The Garden Sprayer

    If youre looking for the best results, start by mixing your chemical solution with a gallon of water, and a quart of chlorine bleach.

    Mix them well and place them in your container. You can even use a pump-style garden hose sprayer to get the job done fast.

    Youre given a lot of leeway in terms of where you want to pour your cleaning agent.

    As long as its a low-pressure sprayer, its all good. But, never pour your solution and use a pressure washer! Youll damage your asphalt shingle in the end!

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    Two Common Types Of Algae On Your Roof

    Fire Moss – Fire Moss is less common than the Gloeocapsa Magma below but is still very prevalent on many roof substrates, from cedar shake to asphalt shingles, it loves to latch on and reproduce. When fire moss gets out of hand, it will push up your shingles allowing water to get underneath and severely degrading your roof.

    Gloeocapsa Magma – This is the old “black streak on my roof” culprit. It is most common on Asphalt shingles and can is a spore based algae, it lives on the limestone in your shingles. When it feeds it degrades the limestone and eventually if left untreated, will take over the whole roof making it look all black when that is not the color of the shingle itself, that is in fact the algae growing on the shingle.

    Roof Moss Removal: Cleaning Mold Algae & Moss From Your Roof

    How to Remove Mold From Your Roof

    We don’t recommend trying to handle roof algae and moss removal on your own. We recommend hiring a professional.

    If you are a DIY person capable of climbing a ladder and not afraid of heights, you may be able to tackle algae or moss removal yourself.

    The safest method for your roof and the environment is to use a product called Spray and Forget or Wet and Forget. These products can be purchased at most local hardware stores, can be put into a hose-end sprayer, and applied in many cases from the ground or a ladder or the edge of the gutter. These methods can take 3-6 months to work but are the safest. Take some time to research these products before use.

    Another more aggressive method for quicker results is the use of water and bleach. Below are the general steps for this method:

    • Mix 1 part oxygen bleach cleaner with 1 part water.
    • Pour the bucket of solution onto the affected area of the roof and let it soak for 30 minutes.
    • For larger sections affected by algae or moss you could put this solution into a spray pump and apply. Be extremely careful not to step on wet algae or moss as it is very slippery and could cause a slip and fall!
    • After 30 minutes, rinse the mixture off with your hose on a low-pressure setting. NEVER PRESSURE WASH YOUR ROOF. The moss won’t come off your roof immediately, but within a few days, it will dry up and blow off with the wind. If your roof is pretty well-covered in moss, you might need to use a leaf blower to get rid of the remains.

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    How To Use Bleach To Cleanroof Shingles

    Using bleach is a fast and efficient way of cleaning and keeping your roof shingles clean. It can be is used to clean stained and dirty roof shingles.

    Some of the items you will need for the method below include water, chlorine bleach, 1 cup of powdered laundry soap, a stiff roof broom/brush, ladder pump garden sprayer, a large bucket, a ladder, gloves, apron, goggles and rubber soled shoes with good gripping.


    Bleach irritates mucous membranes, the skin and the respiratory system. Do not forget to put on protective gear gloves, lab coat or plastic apron, and goggles

    Bleach reacts readily with other chemicals, so caution should be exercised when using this chemical. Ensure the area is well ventilated when diluting or using bleach.Cold water should be used for dilution as hot water decomposes the active ingredient, sodium hypochlorite, rendering it ineffective.

    What Causes Roof Algae

    Algae is a nonflowering aquatic plant that does not have roots or leaves like other plants. Roof algae can develop in certain environments. It thrives in humid atmospheres, where heat and moisture combine. Algae grow fastest in shady, damp areas, such as under large trees. It also needs nutrients to continue surviving on your home. Unfortunately, the limestone filler in most roofing shingles provides nutrients to the algae spores. The inorganic materials found in your roof will allow the algae to survive, spread, and darken.

    Most cases of roof algae or fungus start with a single spore finding its way to your home. The wind can blow a spore onto your roof, and from there it will take off if the conditions are conducive enough. Rainy weather can increase the chances of algae development, but it does not need rain if there is enough humidity in the air. Overhanging branches, clogged gutters, standing water, a porous roofing material, and poor roof ventilation can all cause roof algae. Taking steps to clear your roof of common issues can help you stay ahead of algae growth.

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    Cleaning Roof With Bleach And Water

    Cleaning the roof with bleach and water is one of the easiest and most efficient ways to take care of your shingles. However, following the right procedure is essential to consider in ensuring you experience good results. Here is the step-by-step process on how to go about it.


    • Bleach


  • Use the ladder to climb and inspect the roof so that you can find areas affected by algae, moss, mold, bacteria, mildew, and other micro-organisms.
  • If you have vegetation and plants around your home, make sure you wet them first to protect them from the bleach mixture.
  • Mix the equal parts of the bleach and water in a 50:50 ratio to form a bleach cleaning solution.
  • Pour the mixed solution into the garden hose sprayer.
  • Take your ladder and climb the roof, and then spray the shingles with the solution.
  • Wait for the solution to work on the roofs surface for about 20 to 30 minutes.
  • Finally, rinse with water thoroughly.
  • If you plan to use this method, ensure you do it during morning hours when cloudy and without rain. Also, avoid cleaning on a sunny day because the bleach will evaporate. If you clean and some organisms remain, repeat the process until the roof is sparkling clean.

    Problems With Using Bleach On Asphalt Roofs


    There is some concern regarding the use of chlorine-based productson asphalt roofs. Household bleach can damage asphaltdue to its high sodium content. Apparently, the sodium causes anelectrochemical reaction that reduces the elasticity of the asphalt leading to stiffness, brittleness and curling of the shingles.

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    Do It Yourself And Save Big Bucks

    Professional roof cleaners charge hundreds of dollars the bigger the roof, the more hundreds youll spend. And they have to repeat the cleaning every few years. If your roof slope isnt too steep and youre comfortable working on it, you can clean it yourself and save the dough.

    Youll need a full-body harness, a garden sprayer, a garden hose and a nontoxic, noncorrosive roof-cleaning chemical. Some manufacturers sell a special tool applicator and rinsing tool, but if the staining isnt severe, you may not need them.

    Solving Your Algae Problem

    Rather than resort to yet another round of harsh chemicals and high-pressure water, you can consider the Kelly Roofing Roof Rain cleaning solution:

    • Degreasing agent
    • Sealant
    • Biannual maintenance

    When you partner with Kelly Roofing to take care of your tile roof, you get our years of experience, our dedicated roofers, and our innovative products. Kelly Roofing uses Roof Rain, a 100 percent natural biocide made from oranges. It dislodges the algae and cleans off the black streaks without harming your landscaping or the environment.

    The professional roofers at Kelly Roofing use soft washing techniques to gently and patiently remove the algae, restore the luster of your tiles, and clean them thoroughly. Once the roof is completely dry, our Roof Rain sealant coat, also made from natural products, is applied to stop algae from regrowing. Mildly acidic, this coating prevents algae from finding a home on your home.

    Your roof will then have a 2-year warranty against regrowth of algae, and when the Roof Rain sealant starts wearing off at 2 years biannually Kelly Roofings crews revisit your home and reseal the tile roof.

    This will effectively lengthen the lifespan of your tile roof, saving you time AND money. Plus, instead of having a clean, streak-free roof for a short time between cleanings, you will have a 100% clean roof all of the time!

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