Skip to Main Content

What Is Relative Humidity?: How It Affects Your Crawl Space

measuring air moisture with tool in crawl space

Many of us learned about relative humidity in school but may have yet to grasp its impact on our daily lives. We now realize it’s more than a concept; it’s a phenomenon that significantly affects our homes.

Learn about relative humidity, its effects, and the encapsulation methods that keep your home safe and dry.

What Is Relative Humidity? 

moisture meter in insulation

Relative humidity is a percentage measuring the amount of water vapor (moisture) in the air compared to the maximum amount the air can hold at a given temperature. The maximum amount of water vapor that air can hold varies with temperature. Warm air holds more moisture than cold air.

In simpler terms, relative humidity tells us how “full” the air is with water vapor, and this “fullness” changes depending on the air temperature.

What Is the Optimal Indoor Humidity Level?

mand and woman arms behind heads relaxing on couch

While the Environmental Protection Agency (EPA) doesn’t specify ideal ranges, maintaining an indoor relative humidity between 30% and 60% is generally recommended for comfort and preventing moisture-related problems. This range prevents window condensation in winter and discourages mold growth year-round.

Lower humidity levels outside this range may cause dry skin and cracks in wood furniture, while higher humidity increases dust mite and allergen risks. You can measure humidity with a hygrometer for a direct reading or use a psychrometer, which measures dry-bulb and wet-bulb temperatures.

Why is Relative Humidity Important? 

Indoor humidity that is either too high or too low can cause problems affecting your health and your home’s comfort. Relative humidity is important for the following reasons:

hand adjusting indoor thermostat

The Effects of High Humidity  

  • Mold Growth and Increased Allergies: High moisture creates favorable conditions for mildew and mold growth, increasing allergy symptoms.
  • Structural Damage: Extreme moisture fosters fungi and mold, contributing to musty odors, wood rot, and damage to wooden support beams, floors, and furniture.
  • Utility Bill Increase: High humidity increases HVAC use in warm weather due to cooling inefficiency; in cold winter months, it increases heating use, leading to high energy bills.
sick woman with blanket sneezing into tissue

The Effects of Low Humidity

  • Virus Spread: Some studies suggest that low humidity may allow certain viruses to survive longer.
  • Less Attractive to Pests: Damp crawl spaces attract pests. Lower humidity makes the space less hospitable to these unwanted guests.
  • Foundation Cracks: Very dry crawl spaces can cause cracks in concrete foundations due to shrinkage.

How to Manage Relative Humidity in Your Home 

Manage the humidity level in your home by implementing the following:

crawl space encapsulation installation

Crawl Space Encapsulation 

If you have a dirt crawl space, moisture can seep into your home through the ground, increasing your relative humidity. To avoid this problem, you need to invest in professional crawl space encapsulation.

This entails covering the dirt floor and walls with a 20-mil vapor barrier. What this does is lock out outside air and prevent moisture from seeping through the dirt floor. 

Open exterior crawlspace vent.

Seal Crawl Space Vents

Warmer air holds more water than cooler air. As such, it is common for outdoor air to be more humid during the summer months.

This is also true for homes in the coastal regions because the surrounding air absorbs the water from the ocean. That said, open vents allow warmer outdoor air to circulate your crawl space.

This warm air damps its moisture in your home through condensation, leaving you with a humid crawl space. To prevent this, tightly seal off your crawl space vents and door to prevent outdoor humidity from entering your crawl space. 

dehumidifier in crawl space

Install Dehumidifiers 

Dehumidifying your crawl space or basement is another good way of controlling your relative humidity levels. A dehumidifier clears excess moisture from the air in your home, making the indoors less muggy and less attractive to mold and other thirsty insects and pests. 

If the air in your home feels damp, musty, and uncomfortable, contact JES Foundation Repair to schedule a free crawl space inspection

Have a Humidity or Crawl Space Concern? JES Can Help!

JES Ownership Tour in Baltimore, MD.

Have you noticed damp indoor air or musty odors inside your home? Crawl space moisture should be addressed immediately to prevent damage.

If you reside in Virginia, DC, Maryland, or parts of West Virginia or North Carolina, contact JES for a free crawl space inspection. We protect your home from the inside out, ensuring your family’s safety and health.

    Contact Us For Your Free Inspection

    * All fields are required.

    Crawl Space Humidity FAQs

    Maintaining the correct humidity level in your crawl space is essential for several reasons. It helps prevent structural damage to your home, deters mold and mildew growth, and improves overall indoor air quality. Proper humidity levels also make your home more energy-efficient by reducing the load on heating and cooling systems. Contact us today to learn more.

    Costs vary based on your crawl space size and condition. JES Foundation Repair offers free inspections, no-obligation quotes, and financing options to meet your budget.

    Indicators of high humidity in a crawl space include musty odors, visible mold or mildew, condensation on pipes or insulation, and wood rot. These signs suggest the humidity level is above the ideal range, potentially leading to structural damage and health concerns. Contact us today to schedule your free inspection.

    Related Resources

    Shaye Glisson

    Shaye Glisson

    Shaye is an SEO Content Writer for Groundworks with over twelve years of experience creating helpful content across various industries, including home services and retail. She is a Gulf Coast native and writes from her firsthand knowledge of the area's hurricane and flood impacts on the local community. In her free time, Shaye enjoys exploring the local food and music scenes.

    Publish Date:

    Last Modified Date:

    JES Foundation Repair service area map of the Mid-Atlantic region.

    Our Locations


    8361 Town Center Ct
    Nottingham, MD 21236


    311 Central Rd.
    Suite 2-02
    Fredericksburg, VA 22401

    Hampton Roads & NE NC

    2569 Quality Ct
    Virginia Beach, VA 23454

    Northern VA & DC

    7940 Gainsford Ct.
    Bristow, VA 20136


    309 Quarles Rd
    Ashland, VA 23005

    Southwest Virginia / Roanoke

    2033 Cook Dr.
    Salem, VA 24153

    Western Virginia

    456 Old Courthouse Rd
    Appomattox, VA 24522


    45 W Boscawen St,
    Winchester, VA 22601