6 Tips for Treating Fungus, Algae, and Mosses on Your Roof

Amy Pawlukiewicz
Written by Amy Pawlukiewicz
Reviewed by Ami Feller
Updated January 3, 2022
Fragment of luxury house with nice landscape
Photo: karamysh / Adobe Stock

Reclaim your roof from invasive fungus, algae, and mosses

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Have you noticed multicolored stains or streaks on your roof? If so, it might be time to get out your ladder or call in a professional. Roof fungus, algae, and moss are not only an eyesore, but they can also hurt the integrity of your roof and cause structural damage if not removed quickly. Here’s what you need to know about the different things that can grow on your roof, plus how to treat them.

Types of Roof Fungus

An old roof covered with fungus
Photo: Алексей Пахомов / Adobe Stock

Four main types of fungus can grow on your roof and cause structural problems for your home, as well as become potential health hazards to you and your family. They all have the same root cause: humidity and moisture. If you live in a particularly humid climate, you’re more likely to see fungus growing on your roof.

Algae

Algae is a type of fungus that’s typically a blackish-green color, and it’s attracted to moisture. If not dealt with quickly, algae can eat away at your shingles. When spores land on wet spots on your roof, they will spread and multiply. Be on the lookout for algae if you live in a moist climate.

Mildew

When mildew appears in your shower, it’s unsightly and can be hazardous to your health, and mildew on your roof is no different. Roofs that don’t have good drainage systems are prone to mildew, which spreads rapidly in warm, wet areas. Mildew is usually light gray, pink, or black.

Mold

Mold is the most dangerous type of fungi that can grow on your roof because it’s hazardous to your health. This type of fungus is slimy and black, brown, or dark green. It usually grows on wood and in drywall, where it’s easy for water to permeate. It also has a pungent smell that makes it hard to miss.

Moss

Moss on roof tiles
Photo: magicbones / Adobe Stock

The reason why moss grows on roofs is because of moisture, shade, and debris. And while it can be a beautiful addition to the sides of your home, it comes with some risks. Moss can cause dry rot because it traps moisture in your roof and allows it to seep into the structure. Don’t leave moss unattended on your roof—no matter how much you love those old-world cottage vibes.

Tips to Treat Roof Fungus, Algae, and Mosses

Now that you’ve identified what’s growing on your roof, what can you do about it? Since any job that requires you to work on your roof comes with inherent risks, hiring a professional is always the safer option. However, if the growth hasn’t damaged the roof’s structural integrity, you can take care of it yourself.

1. Make a Rinse

Since bleach kills fungus, start by making a DIY fungus cleaner. While wearing rubber gloves and a protective mask, make a solution that is half bleach, half water. Transfer the solution into a pump sprayer, which will make it easier to distribute it on your roof than pouring the solution from a bucket. You can also buy a pre-made roof cleaning solution from a local home improvement store.

“The product and process of cleaning a roof is often called a ‘soft wash,’” says Ami Feller of Feller Roofing. “it is called a soft wash because it is a very gently process that won't compromise your roof materials with pressure. There are many companies out there that do soft-washing fairly inexpensively. They also can clean the rest of the exterior of the home, sidewalks, driveways and even playground equipment.”

2. Get Out Your Ladder

Removing fungus from your roof means that you have to go on top of it. If you’re comfortable with this step, ensure that you have a harness to secure yourself. Never get on your roof without having someone on the ground to hold the ladder or call for help in case of emergency. Keep in mind that whatever is growing on your roof will make the surface more slick, so call a professional if there’s a lot of growth or you have any doubts about your safety.

3. Spray and Wait

Once you’re up on the roof and secured into your harness, use the pump sprayer to liberally distribute the solution onto the surface of your roof. You should let the solution set for 15 to 60 minutes to kill the growth. The amount of time you leave the solution on the roof should correspond to the severity of the infestation.

4. Rinse

Once you’ve waited the appropriate amount of time, use a garden hose with low to medium water pressure to rinse off your mixture. Start at the top of your roof and rinse downward toward your gutters, and then rinse it thoroughly to ensure you’ve removed all of the solution. 

Since bleach can kill plants or scorch the leaves, rinse off any plants that came in contact with the runoff from the solution. If you’re concerned about damaging your plants below the area where you’re working, you can put down a tarp or plastic sheeting to protect the plants.

5. Check and Repeat

While wearing your gloves, check to see if the roof still feels slimy when you run your hand over it. If it still feels slippery, apply another round of the bleach solution, let it sit for another 10 to 15 minutes, and then rinse it again. If it doesn’t feel slimy, then your work is done.

6. Address Other Roof Issues

There are outside factors that may be contributing to the growth of mold on your roof.  Ensure any overhanging branches are trimmed back, since they allow excess water to flow onto your roof. 

You can also apply a moisture-resistant treatment to your shingles to block out wetness. Check to see that your attic is vented correctly and not trapping heat, which can encourage moisture. Finally, clean your gutters to ensure that debris doesn’t build up, which can trap water.

Additional Precautions

Aside from ladder safety, there are some other precautions to keep in mind while treating your roof for fungus.

  • Never add ammonia to a bleach solution. It creates a poisonous gas.

  • Don’t use a power washer to distribute the solution or rinse, as it can knock off your shingles, or remove their necessary grit.

  • Mixing water with the fungus can make the roof extra slippery, so exercise extreme caution if performing the task yourself.

  • Performing regular maintenance on your roof will help prevent any mold growth.

Hiring a Professional

Hiring a professional to eliminate your roof fungus problem is the best choice to avoid unnecessary safety risks. The cost to hire a professional roof cleaner usually runs between $300 and $600. Professional roof cleaners will be able to quickly identify what kind of fungus is growing on your roof, and then remove it. Since they are trained to work with all kinds of roofing, you also won’t have to worry about breaking your shingles.

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