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

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.

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.

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.

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.

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. 

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. 

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. 

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.