What Is Roof Algae and How Do I Fix It?

What is roof algae?

Your roof can gather more than just dirt and leaves. If you leave it alone, your roof might also get some unsightly stuff like algae. Different types of algae, lichens, and fungi could grow as bacteria move in. Some folks confuse algae with “roof mold.” But usually, it’s this blue-green algae. When it dies, it leaves dark stains on your roof.

Algae can make your new roof look bad with stains and growths. It keeps getting worse each year until you get it cleaned by pros. Learn all about roof algae in this complete guide from the Certa Roofing experts.

Our residential roofing contractors want you to be able to spot roof algae, know the risks it could bring to your home, and when to bring in the experts for cleaning, roof repair, or roof replacement. We provide free roof inspections at locations across the country.

Identifying Roof Algae

When you see dark spots or black streaks on your roof, you might be seeing roof algae, also known as gloeocapsa magma. These marks might look like dirt or mildew, but they’re actually a sign of algae. Let’s look into how to recognize this problem:

  • Appearance:

    Roof algae usually shows up as dark streaks or spots. This happens because the algae makes a protective colored coating to shield itself from strong UV rays, which roofs get a lot of.
  • Affected materials:

    It’s often seen on asphalt shingles, which have fillers like fiberglass and crushed limestone that algae really like.
  • Spread of algae:

    Algae spores aren’t stuck in one place; they float in the air and can move from one rooftop to another easily. That’s why you often see it around your neighborhood.

To figure out what makes algae grow, think about these factors:

  • Environmental conditions:

    Water is a big reason why algae grows. Weather with lots of rain, humidity, or gutters that pour onto the roof can make a perfect spot for algae to thrive.
  • Surrounding flora:

    Trees hanging over the roof give shade but also drop leaves and stuff that can hold water, making it even better for algae to grow.

Even though it’s not harmful, roof algae can still hurt your roof’s lifespan. It can make the protective granules on your shingles break down faster, which could mean leaks sooner. To keep your home looking good and your roof strong, it’s important to clean it regularly. This not only makes your roof last longer but also makes your whole house look better, keeping it in top shape.

Causes and Effects of Roof Algae

Algae is a type of plant that lives in water but doesn’t have roots or leaves like other plants do. Roof algae can pop up in specific places. It likes places that are humid and warm. Algae grows quickest in shady, wet spots, like under big trees. It also needs stuff to keep living on your roof. Sadly, the limestone in many roofing materials gives the algae what it needs. The stuff in your roof helps the algae stick around, spread, and get darker.

Roof algae or fungus usually begin when a single spore lands on your home. If the conditions are right, like when it’s humid or rainy, it can start to spread. Rain helps, but it doesn’t have to rain for algae to grow if it’s humid enough. Things like overhanging branches, blocked gutters, water that stays put, a roof that soaks up water, and not enough airflow can all lead to roof algae. Clearing up these problems can help stop algae from taking over your roof.

Besides looking bad, algae can also harm your roof over time. It wears down some roofing materials, causing damage to the structure. Over time, algae can lead to:

  • Increased solar heat gain.

    Roof algae turn black because they have a pigment that acts like sunscreen for them. But for your home, this black layer absorbs more sunlight. That means your attic gets hotter, and your home overall gets warmer from the sun. You’ll feel this more in the summer.
  • Increased energy spending.

    Because of that extra heat from the sun, your HVAC system might have to work harder to keep your home cool. That means you’ll probably see higher energy bills, especially in upper floors near the attic. And if algae keep growing, your HVAC system will wear out faster, leading to more repairs and higher costs over time.
  • Structural damage leading to leaks & repairs

    If you ignore it for too long, algae can start breaking down the structure of your roof. This can lead to leaks and too much moisture inside your home. In the end, you might have to spend money on fixing or even replacing your roof, which you could have avoided.

Causes and Effects of Roof Algae

Different types of bacteria can show up on roofs in various ways. Sometimes what looks like roof algae might actually be moss, mildew, or mold. Roof algae usually appear black-green. They tend to thrive on surfaces like wood and asphalt shingles or concrete tiles, particularly in areas with little sunlight. One common kind of roof algae is Gloeocapsa magma. It’s a bacterium that feeds on water and releases oxygen. This bacterium is responsible for those black stains you might notice on your roof. These stains are algae buildups that can block the sun from clearing away the bacteria.

Roof lichen is a mix of algae and fungus. When these two team up, they can form living organisms. Lichens use roots to grip tightly onto your shingles, making them tough to remove. If you don’t deal with lichen, it can eventually strip off the top layer of your shingle, leaving a lasting mark on your roof. Roof moss is similar to lichen because it also has root-like parts that cling to your shingles. Moss’s “roots,” called rhizoids, can fasten the moss to your roof. Then, the moss can gather windblown soil and spores to create a layer of algae/lichen growth on your roof.

Unlike algae and moss, mold isn’t a healthy plant. Roof mold can show up as black or brown patches, or as slimy, stinky buildups. Mold tends to pop up where your roof has soaked up water. Mildew is similar; it thrives on damp surfaces and can lead to health issues. Mildew might look powdery and come in various colors, from black to pink. All kinds of roof bacteria bring various risks to your roof, house, and health.

How Many Ways Roof Algae Can Affect Your Roof?

Roof algae mostly affects how your roof looks, but roof mold is more serious. If you leave roof mold alone, it could seriously harm your roofing. So, it’s crucial to address any damage or stains on your roof by getting a professional roof inspection.

Appearance.

One common issue homeowners face with roof algae is how it looks. Many homeowners only notice they have algae when it starts making their roof look bad with black streaks, dark spots, or green mossy patches. Roof algae can really bring down the appearance of your home's exterior.

Home value.

If you're trying to sell your home, having roof algae can cause problems. It suggests that your roof might have significant damage and could need replacing. This could lower the resale value of your home until you get it fixed. Algae and lichen can stick to your roof, leaving permanent stains.

Wood rot.

If moisture seeps into your roof's wood, it could become a big issue. Standing water can make the wood soft and cause it to rot, which can permanently weaken it and make it unsafe. Wood rot can result in roof leaks, costly repairs, and the need for wood replacement.

Mold.

Another danger of trapped moisture in your roof is the potential growth of mold. When standing water and humidity combine with algae spores, it creates an ideal environment for mold to thrive. Mold can pose health risks to you & your family.

Integrity.

If you leave algae and/or mold on your roof, it could harm its structure beyond basic repairs. Allowing algae to spread across your roof for a long time might make the tiles impossible to fix and could drastically shorten the lifespan of a new roof.

Damage to other structures.

Algae spores can hitch a ride on the wind and stick to other structures around your residential property. While roof algae might begin on your house, it won’t take long before you see similar growth on sheds, barns, and carports.

Roof algae, fungus, mildew, moss, and mold can harm your health. Breathing in mold or mildew spores can lead to respiratory problems, allergies, asthma, nausea, vision issues, and other health risks. It’s important to act quickly when you spot algae on your roof.

Cleaning Methods

Having a clean roof does more than improve the look of your home. Roof maintenance also extends the life of your roof and preserves your home’s structure. Algae or mold buildup can discolor your roof and eventually damage your shingles, compromising the roof’s quality and health. This can void your warranty or lower your home’s value. Repairing or replacing a damaged roof is costly, so it’s important to take care of your roof by keeping it clean and well-maintained.

Many service providers in a community offer roof maintenance services. To best serve our clients and community, our team has identified the most effective techniques to remove stains, mildew, algae, and mold from your roof.

High-Pressure Power Wash

High-pressure power washing is a common method for cleaning roofs. It is affordable and quick, but it only suits certain types of roofs. It works well on metal or tile roofs, but the high pressure can permanently damage shingle roofs. Additionally, the pressure might not fully remove algae roots.

Chlorine Bleach Roof Cleaning

Chlorine Bleach Roof Cleaning

Chlorine bleach roof cleaning is an effective way to remove stains. This method uses a mix of chlorine bleach, sodium hydroxide, and other chemicals like trisodium phosphate. The process is simple: apply the chemicals, let them dry, and then reapply. Over the following months, these chemicals work to lighten and remove tough stains, moss, and lichens. 

This method is more cost-effective than others, but homeowners should be cautious. The strong chemicals can impact the environment, potentially harming landscaping or polluting waterways if they bypass runoff recovery systems. Additionally, the harsh odors can be harmful to people, pets, and wildlife. By working with professionals and trusted companies, homeowners can ensure a clean roof while protecting the surrounding environment.

Eco-Friendly, Low-Pressure Wash

Chemical-free, low-pressure roof cleaning is another option for homeowners that is gentle on both your home and the environment. By avoiding phosphates, chlorine bleach, and high-pressure washing, this method removes stains without causing damage. It keeps you and the surrounding environment safe. This gentle cleaning method also protects your landscaping and shingles, making it ideal for older roofs or homes in heavily forested areas.

Eco-Friendly, Low-Pressure Wash
Professional Roof Cleaning

Professional Roof Cleaning

A roofer with a license knows how to deal with algae on your roof. They’ll check your roof, see if the algae caused any problems, and clean it without making things worse. They might suggest stuff like special roof coatings or new gutters to stop algae coming back. And if the algae messed up your roof, they can plan repairs too.

When you spot signs of algae on your roof, get in touch with a roofing pro pronto. Waiting makes it tougher to fix. Save yourself trouble and cash by acting fast. Look out for discoloration, watermarks, dark spots, or peeling paint. If you see mold on your chimney, rotting wood, or crumbly drywall, get a roofing expert on the line ASAP. Ignoring it could lead to property damage and health problems.

Long-Term Solutions

To stop algae from growing on your roof, try these tricks as part of your regular home upkeep:

Tricks How to
Metal ridge flashing Put in galvanized metal ridge flashing for a lasting fix. The stuff it releases makes it tough for algae to grow, so your roof stays nice and clean.
Zinc strips Try putting zinc strips near the top of your roof. When it rains, the zinc washes down over the shingles, making it hard for algae to grow.
Sunlight and trimming Trim back any branches hanging over your roof to let in more sunlight. Less moisture and shade means algae won’t have what it needs to grow.
Algae-resistant shingles When you’re getting a new roof, go for shingles with copper bits inside. They’re made to fight off algae, giving your roof an extra layer of protection.
Copper or zinc strips If your roof’s already up, add copper or zinc strips. They let out ions that stop algae for about twenty years.
Chemical treatments Pros can use chemicals like copper sulfate on your roof to make it unfriendly for algae. But remember, let the experts handle it, and you might need a touch-up every few years.
Professional cleaning Having a pro clean your roof regularly doesn’t just make your home look good—it also stops algae from building up.

Follow the above tips, and your roof will stay strong and look good, without the ugly and harmful effects of algae.

Do You Need Roof Repair, Cleaning, or Replacement?

When you bring in a contractor to handle roof algae, they can spot when your shingles are beyond fixing. You might miss signs of shingle trouble or wood rot, but a contractor won’t. They’ll find these problems and suggest what to do next. You might just need algae cleaning, shingle fixing, swapping out a few shingles, or even a whole new roof, depending on how bad things are.

If algae only messed up a few shingles, fixing them should do the trick. But if it’s spread deep into your roof, or most of your tiles are affected, or if your roof’s just old, getting a new one might be smarter. A reliable contractor like Certa Roofing can tell you what’s what. And if you do need a replacement, we’ll hook you up with a top-notch roof and a lifetime warranty.

Conclusion

It’s really tough to stop roof algae if you’re in a humid or damp place. You can’t stop spores from landing on your roof, but you can stop them from growing. Trim all the trees that hang over your roof to let more sunlight in, which stops algae. Keep your gutters clean and remove stuff from your roof quickly. If algae is a big issue where you live, think about getting roofing that fights algae or use special chemicals on your shingles. If you see algae or mold on your roof, don’t try fixing it yourself. Get a professional roofer who has the right tools to handle the problem.

If you see dark spots on your roof, get in touch with Certa Roofing now to see how they can assist you. Just call us or fill out their simple online form.

FAQ's

You can make your own cleaning solution to get rid of algae and moss. Mix equal parts water and bleach together. This mixture is strong enough to kill off the algae and moss but gentle enough not to harm your roof and shingles.

Algae grows on the little bits of limestone in your asphalt shingles. As it grows, it eats away at the limestone, making your shingles weaker over time. Algae can also team up with fungus to form something even tougher called lichen. Lichen is really tough, more damaging, and tougher to get rid of compared to just algae.

Here’s a good mix: Combine one quart of bleach with one water gallon and add 1/4 cup of heavy-duty cleaner, such as trisodium phosphate. Avoid using cleaners with ammonia because they make dangerous fumes when mixed with bleach. Or, for a plant-friendlier option, mix 1 cup of oxygen bleach with 1 water gallon.

A mix of bleach and water is a great way to clean a roof with algae. Just mix equal parts bleach and water, let it sit for an hour, then rinse off the dirt and grime. This combo is safe and strong, giving better results than other cleaning methods.

Scroll to Top