How to Prevent Mold and Mildew Growth On House Siding
May 09, 2025
Mold, Mildew, Moss, and Lichens, OH MY!
Do you know the difference between these green growers? Do you know how to react when you see them on your house siding?
Keep reading to learn more about what they are, what you can do to prevent them, and whether they should affect your house siding choices.
Mildew
What Is Mildew?
Mildew is a fungus, a type of mold. It loves wet, shaded areas with little circulation. These conditions foster mildew growth:
- High humidity
- Lack of direct sun
- Overhanging trees that block airflow
- Sprinklers that frequently wet your siding
- Poor foundation drainage
Should Mildew Affect My House Siding Choices?
Mildew can grow on all kinds of surfaces, but certain types of house siding are more susceptible to mildew.
- Fiber cement siding, sometimes called Hardie board
- Stucco siding
- Wood siding, including engineered wood
- Vinyl house siding
How Do I Prevent Mildew On My House Siding?
The best way to help prevent mildew from growing on your home is to take preventive measures. Although you cannot fix every condition that mildew loves growing in, you can:
- Solve your foundation drainage problems by talking to a landscaping or foundation professional.
- Relocate sprinklers to prevent them from dampening your siding.
- Trim trees and shrubs away from your home to improve air circulation.
How Do I Clean Mildew Off My House Siding?
If you find mildew growing on your house siding, you can remove it using a pressure washer and a commercial mildew remover. Follow the instructions on the product packaging for best results. Always check your siding warranty to ensure your cleaning methods won’t void it.
Some homeowners may be tempted to use chlorine bleach to remove mildew. However, chlorine evaporates too quickly to kill the mildew, which can cause regrowth. Chlorine bleach can also damage or discolor your siding, harm nearby plants, and corrode any metal fasteners or flashing it comes in contact with.
Hydrogen peroxide, also called oxygen bleach, is a better alternative to chlorine bleach if you want to remove mildew from your house siding. Hydrogen peroxide breaks down into water and oxygen, so it’s safe for plants and most siding choices for houses. It penetrates porous surfaces to kill mildew from the root and prevent regrowth.
Mold
What Is Mold?
Mold is a fungus. Its spores travel through the air. If the spores land on something moist, they may begin consuming and digesting anything they can to survive, such as wood and other household construction materials.
Mold loves moisture, organic materials for nutrients, and oxygen. It thrives best in temperatures between 40 and 100°F.
What Types of Siding Does Mold Grow On?
Mold strongly prefers siding made of organic materials, like wood or engineered wood. However, even siding made of inorganic materials, like vinyl, can still foster mold growth. This is because organic materials can collect on the surface of your house siding and provide mold with the nutrients it needs to thrive.
How Do I Stop Mold From Growing On My House Siding?
Like mildew, prevention is the best way to avoid mold on your siding. Clean your gutters, remove organic material growing on or near your siding, and ensure any ductwork that opens outside your home is free from moisture.
If you do need to remove mold from your house siding, you can use a mixture of 30% vinegar and 70% water, or dilute a quart of oxygenated bleach per gallon of water to use as a cleaning solution.
A Note On the Dangers Of Mold and Mildew
Mold and mildew can be dangerous for humans and pets. They are especially harmful for people with allergies, asthma, or weakened immune systems. Exposure to certain types of mold can trigger allergic reactions, respiratory issues, and fungal infections of the lungs. This is why it’s important to quickly address the growth of mold and mildew on your home.
For bad mold problems, look into professional remediation. It’s worth it to help save your house siding at any cost – and to protect your family.
Lichens
What Are Lichens?
Unlike mold and mildew, lichens are more complex. A lichen is made up of two living things, working in symbiosis.
- a fungus that serves as the shelter
- an algae that makes its own food using photosynthesis
Lichens can live in harsh conditions and come in many colors and shapes. Some look like crusty patches or little leaves. When they grow on your siding, they can cause damage and discoloration.
Why Do Lichens Seem to Love My House Siding?
Because lichens are kind-of a mold and kind-of an algae, they love house siding, but they’re so tough, they can truly grow anywhere, even on rocks. They love clean air, a little bit of sunlight, and a little bit of moisture.
How Do I Remove Lichens From My Siding?
Lichens can harm exterior wood surfaces, gouging out small notches and grooves over time. This can hold rainwater and lead to rot or other water-related damages. If you see lichens growing on your home exterior, act fast, because they can be tough to remove.
Removing lichens requires you to:
- Remove the organism.
- Clean the siding surface.
- Protect against future infestations.
Start by cleaning away organic debris. Use a push broom or similar brush to remove stuck-on patches of lichen. Then, spray on a combination of vinegar, water, and a tiny amount of dish soap. The soap helps the vinegar stick to the lichen.
After a few days, you’ll notice that the lichens have begun dying off. Once dead, use your broom or similar brush to remove any remaining pieces of lichen. Rinse any remaining residue with a garden hose.
Moss
What Is Moss?
Moss is a type of simple plant that doesn’t have flowers, seeds, or roots. It has tiny thread-like structures called rhizoids that help it cling to surfaces and soak up water.
It reproduces with spores rather than seeds. These tiny spores float through the air until they land somewhere damp and shady, where they like to grow. Moss looks like green fuzzy patches, similar to a carpet.
What Types Of House Siding Does Moss Grow On?
You’re most likely to see moss on your roof, but it can cling to and grow on siding surfaces, especially those made of wood or engineered wood.
How Do I Stop Moss From Growing On My House?
Like with mold, mildew, and lichens, your best bet to stop moss in its tracks is to reduce moisture and improve airflow around your home. Remove any organic matter that these pesky plants and fungi can cling to, especially from your gutters. Use any of the gentle cleaning methods prescribed for mold, mildew, or lichens to address moss growth.
Should Mold, Mildew, Moss, and Lichens Affect My House Siding Choices?
Fears of mold, moss, mildew, or lichens shouldn’t steer you away from any siding in particular. But if you know your home is prone to developing it, it’s wise to select a house siding that is less hospitable for these pesky green growths.
Certain types of house siding, like wood, engineered wood, stucco, or fiber cement board, can help create ideal environments for growth. Even vinyl siding can develop mildew or mold over time – but it tends to be easier to clean. Seamless polymer siding, a patented siding product made of polypropylene resin, resists mold and mildew growth.
