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Guide for Algae & Moss Removal on Your Roof

July 22, 2020

Roof with streaks of mold on it.

If you live in the South, Midwest, or another region of the country that has warm, humid summers, you may have noticed stains and streaks showing up on your asphalt shingles. These stains look a lot like mold—but in fact, much of this so-called mold is actually blue-green algae (Gloeocapsa Magma). In some cases, what looks like mold might be more properly classified as moss.

In less frequent instances, the streaks on the roof actually are mold, which can be very dangerous for your family and more difficult to get rid of. The most serious mold cases can cause asthma, headaches, and other health problems, so it’s crucial to understand the difference.

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, it’s 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.

Another Less Common Occurrence is Moss

Roof moss removal

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 chlorophyll—the 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. 

Difference Between Moss and Algae

Though they might be grouped as the same thing because they grow in the same area of your home, moss and algae are actually quite different and distinct. 

Moss always appears more green and fluffy-looking than algae, though it might appear browner during dryer seasons. Moss will also grow up off the roof, while algae will grow flush to the shingles and fixtures, staying flat and unobtrusive. Algae will appear in many different colors such as gray, blue, green, or brown. 

A small amount of moss is relatively harmless, but left unattended, it can grow and eventually damage your asphalt shingles. Moss should be removed. Algae actually fosters the growth of mold, which can lead to very serious issues. Algae, too, should be removed quickly and efficiently. 

Roof Moss Removal: Cleaning Mold, Algae, & Moss 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. (Add ½ cup per gallon of trisodium phosphate for a stronger cleaning solution.)
bleach in a bucket for roof cleaning
  • 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!
  • Be patient. Allow the mixture to sit for approximately 30 minutes. During this time, the chemicals are killing the algae and moss and loosening its hold on your roof. Take precautions as this mixture can run off your roof and into your garden below so before you spray, cover any plants you wish to keep alive and rinse/wet everything down this solution may come in contact with.
  • 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.

Being up on your roof and tackling this kind of problem can lead to more issues and even put you in danger. So, while clearing away your roof of moss or algae can be done on your own, we don't recommend it. We recommend hiring a professional who knows exactly how to remove these unwanted organisms/plants safely and effectively.

Tips to Prevent Roof Algae & Moss

Roof algae and moss usually grow because of moisture and bacterial growth. You can stop that growth from ever starting in the first place, effectively making your roof last longer. Here are a few ways to prevent future growth once you have gotten rid of moss and algae:

  • Trim trees near the home: Overgrown trees often spread bacteria onto the roof and cause algae growth. Make sure to plant trees far enough away from the house and trim them back regularly so they aren’t hanging over the roof.
tree branch being cut
  • Get rid of standing water: Standing water is another factor that can contribute to mold and algae growth. Minimize standing water on the roof by fixing shingles, cleaning gutters, and performing small roof repairs as necessary.
standing water on a roof

How to Make Your Roof Last Long

Moss and algae growth, if left unchecked, will shorten the lifespan of your roof. In fact, there are several things you can do to extend the life of your roof, most of which involve keeping it clean and clear of debris and growth, such as:

  • Clean gutters
  • Keep attic ventilated
  • Have an annual roof inspection

All of these suggestions revolve around the similar idea that keeping things clean and organized will ultimately keep your roof lasting longer. Roof moss removal and algae removal will also certainly keep your roof functioning properly for a longer period. Take a look at some of the following tips to help prevent growth. 

Contact Roof Maxx

For a roof inspection you can trust and another way to extend the life of your roof, contact us at Roof Maxx. We can apply our sustainable, affordable treatment to add up to 15 years to the life of your roof. Some, but not all, of our dealers offer a roof cleaning service.

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