Maintaining the correct basement humidity is important for your comfort and the integrity of your home. High humidity in basements can lead to mold growth, damage to belongings, and respiratory issues, while overly dry conditions can cause structural problems. With proper monitoring and the right equipment, you can effectively manage basement moisture throughout all seasons.

You’ve heard the phrase: “It’s not the heat, it’s the humidity.”This common expression inspires knowing nods or annoyed eye rolls. But when it comes to your basement, humidity isn’t just about comfort—it’s about protecting your home’s foundation and your family’s health.

Humidity describes the amount of water vapor in the air, but when we’re talking about comfortable and safe basement environments, it’s relative humidity that matters most.

Relative humidity takes into account air temperature, says Kelly Smeltzer, indoor air unit enforcement coordinator at the Minnesota Department of Health.

“We know that the air can hold a maximum amount of water at each temperature,” Smeltzer says. “Relative humidity is the ratio of how much water vapor is in the air compared to how much potentially could be in the air at that temperature.” Smeltzer adds, “Dew point is the temperature when air hits 100% relative humidity.”

But back to your basement. Smeltzer says indoor and outdoor humidity are measured the same way, and maintaining the ideal basement humidity is crucial. He advises keeping your basement’s relative humidity within seasonal ranges. The U.S. Environmental Protection Agency (EPA) recommends maintaining indoor relative humidity between 30 percent and 50 percent to prevent mold growth and maintain good indoor air quality. This general guideline applies to all indoor areas, including basements.

Does a dehumidifier cool a room?

While dehumidifiers do not directly lower the temperature of a room, they can make it feel cooler by reducing humidity levels. High humidity makes the air feel muggy and uncomfortable because moisture in the air slows sweat evaporation, which is the body’s natural cooling mechanism. By capturing excess moisture, a dehumidifier enhances evaporative cooling, making the environment feel more comfortable even though the ambient temperature remains unchanged.

Why Are Basements Humid?

Basements are humid because they’re underground and often lack great ventilation.

The naturally cool and enclosed nature of basements makes them prone to moisture issues.

“Since basements are below grade, they have a lot more contact with the soil than the rest of the house,” says Smeltzer. “Water can seep into the basement from the soil, from poor grading around the landscape, and from cracks that develop in the foundation over time.”

Many homeowners also have laundry rooms and bathrooms in the basement, and Smeltzer says these contribute to higher humidity levels due to steam and water use. If not properly ventilated, this excess moisture can build up quickly. Dryers and basement showers must be vented outdoors to prevent damp conditions.

Additionally, materials such as drywall and flooring in finished basements can hide moisture issues behind walls and under floors. Before renovating, it’s crucial to address any existing moisture problems to prevent mold growth and structural damage.

The problem of Basement Humidity

High humidity in your basement isn’t just uncomfortable; it can lead to significant health problems and structural damage to your home.

“A lot of our common indoor allergens thrive in humid environments,” says Smeltzer. Mold, dust mites and insects are drawn to damp spaces, and their presence can trigger allergies and asthma.

Mold needs moisture to grow, and a humid basement provides the perfect conditions. When warm, moist air meets cool surfaces, condensation forms, creating an ideal environment for mold. “The higher the relative humidity in your home, the more likely you are to have condensation problems that lead to mold,” says Smeltzer.

Once mold takes hold, it can spread quickly and be difficult to remove. It can grow on drywall, flooring, paint, wood studs, carpet, and paneling. Nearly any surface in your basement can become a breeding ground for mold.

What Should Basement Humidity Be in Summer?

Summer indoor relative humidity (including the basement) should be less than 60%, Smeltzer says. Inexpensive hygrometers can be purchased at hardware stores to help you keep track of basement humidity and take action if needed.

What Should Basement Humidity Be in Winter?

Winter indoor relative humidity (including the basement) should be between 20% and 40%, with regional variation, Smeltzer says. Colder climates, such as the Upper Midwest, typically experience lower humidity levels during winter. However, if levels drop too low, it can cause issues such as dry air and static electricity.

Tips for Lowering Basement Humidity

Smeltzer recommends the following steps to ensure your basement stays cool and dry all year round.

Address water sources first

  • Repair leaks and mop up spills quickly. Mold only takes 24 to 48 hours to grow when there’s a moisture source.
  • Use sump pumps to remove water from your basement.
  • Slope soil away from the foundation to direct water away from basement walls.
  • Seal cracks and gaps in windows, doorways and walls to prevent moisture infiltration. Simple solutions like caulking and weatherstripping can effectively close these openings.
  • Don’t overwater plants as. Plants hate soggy roots, and the excess moisture can raise the humidity in your home.
  • For immediate moisture absorption, consider using chemical absorbers like silica gel in problem areas—these are inexpensive options available at most home improvement stores.
  • Regularly check for signs of condensation on pipes and cold surfaces, which indicates humidity levels are too high.

Improve ventilation and air circulation

Proper airflow is crucial for controlling basement humidity. Stagnant air allows moisture to settle and concentrate in problem areas.

  • Install exhaust fans in basement bathrooms. After showering, use the exhaust for 30 to 60 minutes.
  • Use humidifiers sparingly.
  • Vent dryers and other appliances outside of the house to prevent moisture buildup indoors.

Using a dehumidifier

When selecting a dehumidifier, sizing is critical. An undersized unit will run constantly without effectively controlling humidity, while an oversized one might cycle too frequently and wear out prematurely.

  • Use humidifiers sparingly. Dehumidifiers in the summer reduce basement humidity.
  • Position your dehumidifier centrally with adequate clearance around it, and ensure you regularly clean filters and empty the collection tank.

FAQs

What is the best humidity level for a basement?

The ideal basement humidity level is between 30% and 50% year-round, though this varies seasonally. In summer, keep humidity below 60% to prevent mold growth. In winter, humidity between 30-40% is generally recommended, though in very cold climates, slightly lower levels (20-30%) may be necessary to prevent condensation on windows and exterior walls.

Can high humidity damage my basement?

Yes, high humidity can cause significant damage to your basement and home. Excessive moisture can lead to mold growth, wood rot, rust on metal fixtures, deterioration of drywall and insulation, and even structural damage to your foundation. High humidity also creates an environment conducive to dust mites and other allergens that can affect indoor air quality and health.

What size dehumidifier is best for my basement?

The appropriate dehumidifier size depends on your basement’s square footage and typical humidity levels. As a general guideline:

  • Up to 500 sq. ft.: Use a 10-pint dehumidifier.​
  • 500–1,000 sq. ft.: Use a 14-pint dehumidifier.​
  • 1,000–1,500 sq. ft.: Use an 18-pint dehumidifier.​
  • 1,500–2,000 sq. ft.: Use a 22-pint dehumidifier.​
  • 2,000–2,500 sq. ft.: Use a 26-pint dehumidifier.​

For damp environments or areas with high humidity, consider increasing the capacity by 10 pints to ensure optimal performance. Features like automatic shutoff and continuous drainage can enhance convenience by reducing the need for frequent manual emptying.

How can I tell if my basement has a humidity problem?

There are several signs that indicate your basement may have excessive humidity:

  • Visible condensation on windows, pipes, or walls.
  • Musty, damp odors that persist even after cleaning.
  • Visible mold growth on surfaces.
  • Warping or damage to wood elements.
  • Peeling paint or wallpaper.
  • Rust on metal surfaces.
  • Efflorescence (white, powdery mineral deposits on concrete or masonry.)
  • Readings above 60% on a hygrometer.

If you notice any of these signs, it’s important to address the humidity issue promptly before it leads to more serious damage.

About the expert

Kelly Smeltzer has worked for the Minnesota Department of Health in the Indoor Air Unit for over 10 years. Her responsibilities include public outreach and education on Indoor Air Quality (IAQ) concerns, inspections related to air quality laws, and coordination of the unit’s enforcement activities.

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Ally Childress
Ally Childress writes practical, informed stories and how-to guides for Family Handyman and Reader’s Digest. An experienced electrician, Ally's beat naturally includes electrical and construction topics. She also tackles cleaning, gardening, technology, bugs and anything else you can throw at her. She has a knack for finding just the right subjec...
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