Mold Vs. Mildew (When to Worry and When to Clean)

july 9TH, 2020 UPDATED 8:00PM CT
Mold vs Mildew - What's the difference and what should you do - San Antonio Roofing

So you have mold and/or mildew build-up on your roof, now what? Mold and mildew are some of the most common problems when it comes to roofing. But what causes mold and mildew to grow and why is it such a problem? Today we’ll answer both of these questions and learn when to clean vs. when to worry about your mold and mildew problems. So let’s get started.

What is the difference between mold and mildew?

The terms mold and mildew are commonly used interchangeably but they are actually two different things. Mold is a species of microscopic fungus that grows anywhere there are problems with moisture. Mold can build up on clothing, paper, ceilings, walls, floors, and roofing.

Mildew is a specific type of mold and typically has flat growth behaviors. It’s also found wherever there are high moisture levels but is most commonly found around window sills, showers, and similar places.

What is algae?

Algae is a type of plant that can grow on your roofing. Like mold and mildew, algae thrives in moist environments. It’s commonly found growing on roofs because it uses the sunlight for photosynthesis (as its food and water source). This makes your roof the perfect place for algae to grow. Depending on what type of algae is growing on your roof, it could also be a health concern.

The main difference between mold and algae is that algae feeds on the powder in asphalt shingles, while mold feeds on the organic matter that has fallen onto your roofing. The good news is that roofing companies really don’t care about the differences because most cleaning products and solutions are designed to kill mold, mildew, algae, and other similar build-ups all at the same time.

How do you remove mold, mildew, and algae on your own?

If you only have small amounts of mold, mildew, or algae on your roof, you may be able to clean it yourself. The standard method for removing buildup from asphalt shingles is to mix chlorine bleach with water and spray it on the spot. Once sprayed, allow the solution to sit for 5-10 minutes and then rinse off with your garden hose. Keep in mind, however, that if you leave the bleach sitting on your roof for too long it can damage your shingles. Bleach also has a tendency to kill other living things like plants so you need to be sure to remove it well to prevent it from leaking down into your gutters during a rainfall.

Is it safe to clean my own roof?

It depends. Do you have experience climbing on roofs? Do you have the proper safety equipment to climb on your roof without injury? If you answered no to either of these questions, you probably shouldn’t be cleaning your own roof – especially if it has a steep slope. Flat roofs can be safer to climb on, but there is still a risk that there could be soft spots in the roofing that you could fall through. If you don’t how the knowledge or experience to clean your roof, it’s a job that is best left to the professionals.

What do professionals use to clean roofs?

If you hire a professional to clean your roof, they won’t be using bleach and water. Rather, they will use a stronger commercial roof cleaning product. A professional roof cleaner will not only be able to clean clearly visible mold from your roof, but will also be able to check in the harder to see spots. They can also suggest maintenance tasks that can help you to prevent mold and mildew growth from reoccurring.

How can I prevent mold and mildew growth?

As we mentioned earlier, mold and mildew travel through the air and eventually land on your roof. Unfortunately, there’s nothing you can do to stop this from happening. With that being said, mold and mildew will not nest on your roof unless it is in a certain condition. If your roof is dry and clean, mold and mildew won’t be able to thrive there. But if moisture buildup is an issue, this will create the perfect environment for mold and mildew to expand.

In return, the best way to prevent mold and mildew buildup on your metal roofing or roof shingles is to have bi-annual inspections. A professional roofer will be able to take a quick look at your roof to ensure that there are no leaks or problems that could cause moisture damage. In other words, they can catch problems before they occur.

Of course, there are other things that you can do yourself to help prevent the buildup of mold and mildew as well. This includes, but is not limited to:

Trimming the tree branches around your roof. 

In order to prevent mold and mildew build-up, as well as pest infestations, tree branches should be at least 6 feet away from your home.

Keeping your gutter clean. 

It doesn’t take long for dirt and debris to clog up your gutters and when it does water cannot flow freely, resulting in moisture. Clean your gutters regularly to prevent this from happening.

Adding ridge vents. 

When your roof can breathe, moisture buildup is less likely. Ask your professional roofing contractor about the installation of ridge vents and how they can benefit you.

Installing zinc or copper strips. 

Copper and zinc both contain minerals that act as natural repellents for mold. You can install strips made of these metals under your shingles and when it rains the metal will run off onto your roof, preventing mold and mildew buildups as it does.

Consider a moisture-resistant roofing material. 

Copper and other metal roofing materials are your best fight against mold and mildew buildup. Alternatively, you could invest in a specialized treatment for your shakes or shingles.

What are algae resistant shingles?

If you are concerned about roofing mold, mildew, and algae buildup, you could also consider installing algae resistant roof shingles. Ask your local contractor about resistant shingles that can inhibit the growth of algae on your home and roof. Always be sure that you request non-toxic shingle options for the health and safety of your home and environment around it.

Do I have mold damage?

If you have already noticed mold on your roof, you could have mold damage. It’s important that you check your roofing thoroughly so that you can catch small problems before they become big ones. Here are some things to look for that can help you determine if you have mold damage:

Watermarks. Check along the ceilings and walls in your attic for any signs of dripping water or water marks. If you have some, you may have a small leak in your roof.

Discoloration. Any discolorations or dark spots in your attic or on your paint could be caused by moisture damage. Repair it quickly to prevent mold and mildew growth.

Peeling paint or plaster. These can both be signs that water has started to leak in and can be a cause of concern.

Rotting wood. When wood gets wet, it starts to rot. Rotting wood is not only a problem for mold and mildew but it also attracts pests and insects. If you have rotting wood, you’ll want to have it repaired promptly.

Other signs that you may have a problem with moisture include crumbing drywall, musty smells in your attic, or any water leaks or seepages.

Why does it matter?

Most homes that have mold and mildew buildup are the same homes that are vulnerable to roof leaks. And once the mold spreads from your roof into your home, it now becomes a health hazard. Molds can travel throughout your home through your HVAC system, allowing toxins to spread through your air. Molds have been linked to a variety of health concerns including asthma, allergies, and other respiratory problems. For this reason, mold and mildew growth should be dealt with promptly.

Trimming the tree branches around your roof. 

In order to prevent mold and mildew build-up, as well as pest infestations, tree branches should be at least 6 feet away from your home.

Keeping your gutter clean. 

It doesn’t take long for dirt and debris to clog up your gutters and when it does water cannot flow freely, resulting in moisture. Clean your gutters regularly to prevent this from happening.

Adding ridge vents. 

When your roof can breathe, moisture buildup is less likely. Ask your professional roofing contractor about the installation of ridge vents and how they can benefit you.

Installing zinc or copper strips. 

Copper and zinc both contain minerals that act as natural repellents for mold. You can install strips made of these metals under your shingles and when it rains the metal will run off onto your roof, preventing mold and mildew buildups as it does.

Consider a moisture-resistant roofing material. 

Copper and other metal roofing materials are your best fight against mold and mildew buildup. Alternatively, you could invest in a specialized treatment for your shakes or shingles.

Schedule a Roof Inspection with the Experts at

McAllen Valley Roofing Co.

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