Your Guide on How Do You Keep Moisture Out of a Dirt Crawl Space

Moisture in a dirt crawl space can cause various crawl space issues such as structural damage, mold growth, and poor indoor air quality. It can also reduce energy efficiency by allowing damp air to circulate, making it harder to heat and cool your home. 

At Star Spray Foam, we provide expert insulation solutions to protect your home from excess moisture. Proper sealing, ventilation, and insulation are essential for keeping crawl spaces dry and maintaining a healthier indoor environment.

Don’t let moisture take over your crawl space—contact us today and let us help you create a drier, more energy-efficient home!

What Causes Moisture in Crawl Spaces?

Crawl spaces trap moisture due to a combination of environmental and structural issues. High humidity, poor drainage, and improper ventilation contribute to damp conditions, leading to mold growth and wood damage. Here are the most common causes:

• High Humidity: When humidity levels exceed 76.4%, condensation forms, allowing wood beams and subfloors to absorb moisture.
• Poor Drainage: Water collecting around the foundation is often due to ineffective drainage. In cities like New Orleans, where heavy rainfall is common, crawl spaces are especially vulnerable.
• Leaky Pipes: Even a small plumbing leak can introduce excessive moisture into a crawl space over time.
• Open Foundation Vents: Some older homes have a vented crawl space with foundation vents designed to allow airflow, but they often let in humid air instead, worsening moisture problems.
• Improper Soil Slope: If the ground slopes toward your home, rainwater can collect near the foundation, making moisture problems worse.

To prevent these issues, it’s necessary to take a proactive approach in managing crawl space conditions.

How to Keep Moisture Out of Crawl Spaces

Keeping moisture out of crawl spaces protects your home’s structural integrity, prevents mold growth, and improves air quality while enhancing energy efficiency.

1. Install a Vapor Barrier

A vapor barrier is one of the most effective ways to stop moisture from rising through the ground. Using heavy-duty polyethylene sheeting that is at least 6 millimeters thick creates a protective layer that keeps moisture from seeping up into the crawl space. By stopping air movement, vapor barriers help maintain a stable temperature in the crawl space, preventing issues like mold and odors.

For the best results, the seams should overlap by at least 12 inches and be sealed with waterproof tape. Extending the barrier up the crawl space walls and securing it with an adhesive provides additional protection. When moving or working in the space, it’s important to avoid damaging the material to maintain its effectiveness.

2. Improve Exterior Drainage

Water should never be allowed to collect near a home’s foundation, as this can lead to moisture problems in crawl spaces. Proper drainage helps direct water away from the house, keeping crawl spaces dry. 

Proper drainage not only keeps crawl spaces dry but also prevents moisture from affecting the first floor of your home. Installing gutters and downspouts that carry water at least 6–10 feet away from the foundation is essential.

Additionally, using French drains or gravel trenches helps move water away from the home, reducing the risk of pooling. Soil should also be graded so that water naturally flows away instead of collecting around the foundation.

3. Seal Crawl Space Vents

Open vents allow humid air to enter the crawl space, worsening moisture issues instead of preventing them. Instead of improving airflow, vents can trap damp air inside, leading to condensation and mold growth.

To prevent this, airtight vent covers should be used to block moisture from entering. Sealing openings with foam board insulation adds another layer of protection, and applying waterproof caulking around any gaps ensures a complete seal. Sealing vents also helps prevent harmful gases like radon from entering the home.

4. Use a Dehumidifier

A dehumidifier helps regulate moisture levels and keeps humidity between 30–50%, which reduces the risk of mold, mildew, and wood rot. When choosing a dehumidifier, it’s best to select one that is specifically designed for crawl spaces and has a capacity of at least 30 pints per day. 

Maintaining proper humidity levels also helps protect heating and cooling systems from moisture-related issues.

To keep it functioning properly, the water reservoir should be emptied regularly or connected to a drainage system. Using a hygrometer allows homeowners to monitor humidity levels and make adjustments as needed.

5. Insulate Crawl Space Walls and Floors

Applying spray foam insulation to crawl space walls helps reduce moisture buildup and prevents outside air from affecting indoor temperatures. Insulation provides several benefits, including preventing condensation on cold surfaces, blocking moisture from seeping into wood structures, and maintaining energy efficiency, which helps lower heating and cooling costs.

Proper insulation also ensures that heating and cooling systems operate more efficiently, reducing energy costs.

6. Fix Plumbing Leaks Right Away

Even a minor plumbing leak can introduce a steady source of moisture into a crawl space. Regular pipe inspections help catch problems early before they lead to bigger issues. Regular inspections also help protect electrical wiring and other essential systems from moisture damage.

Signs of trouble include damp or discolored subflooring, rusted pipes or fittings, and musty odors near plumbing. Fixing leaks quickly prevents moisture buildup and protects the surrounding structure from damage.

7. Grade the Soil Away from the Foundation

Rainwater collecting near the foundation can easily seep into crawl spaces, leading to moisture issues. Proper soil grading helps redirect water away from the home. 

The ground should slope at least 6 inches over 10 feet away from the foundation to prevent water accumulation. Unlike a full basement, a properly graded crawl space can be more effective in preventing water accumulation.

Homeowners should also be mindful of landscaping designs that trap water near the structure. If necessary, gravel trenches or other drainage solutions can be installed to further control water movement and keep crawl spaces dry.

Why Keeping Crawl Spaces Dry Matters

Taking steps to keep your crawl space dry has long-term benefits for your home’s structure, indoor air quality, and energy efficiency.

While an unfinished basement offers more usable space, a crawl space can be more cost-effective and easier to maintain.

Protects the Home’s Structure

Moisture can weaken wooden beams and floor joists, compromising the structural integrity of your home. Installing a vapor barrier and proper insulation helps protect these critical support structures.

Improves Indoor Air Quality

Since 40% of the air inside your home, especially on the first floor, comes from the crawl space, keeping humidity under 76.4% reduces musty odors and mold spores, improving overall air quality.

Reduces Mold and Pest Issues

Damp conditions attract termites, rodents, and mold growth, leading to various crawl space issues. Sealing off moisture sources keeps pests out and lowers the risk of fungal buildup.

Lowers Energy Costs

A dry crawl space helps insulation work more effectively, reducing temperature swings inside the home and improving the efficiency of heating and cooling systems. This leads to:

• Lower heating and cooling costs.
• A more stable indoor temperature.
• Less strain on the HVAC system.

Regular Maintenance and Monitoring

Keeping moisture out of a crawl space requires regular attention. Here’s how to prevent issues before they start:

• Check for moisture buildup: Look for standing water, damp insulation, or condensation. Small issues can quickly turn into bigger problems.
• Keep drainage systems clear: Remove debris from gutters and downspouts, and extend them at least 10 feet away from the foundation.
• Inspect vapor barriers: Replace any damaged sections to maintain a strong moisture defense.
• Monitor humidity levels: Use a hygrometer to track moisture levels and prevent them from rising above 50%.

Controlling air movement is also crucial in maintaining a dry and healthy crawl space environment.

Protect Your Home from Moisture Issues

A dry crawl space leads to a stronger home, cleaner air, and lower energy costs. Proper moisture control—sealing vents, installing a vapor barrier, improving drainage, and monitoring humidity levels—helps prevent damage and costly repairs

At Star Spray Foam, we specialize in high-performance spray foam insulation, offering open and closed-cell options to create a long-lasting barrier against moisture and energy loss.

Protect your home and save on energy costs by addressing moisture issues today. Call us now for expert insulation and moisture control solutions!