Crawl Space Mold Removal:Causes and How to Clean It Up

What Causes Mold in Your Crawl Space?

Mold grows in a crawl space mainly because of moisture. When the area under a house stays damp for a long time, it becomes the perfect place for mold to live. Water can get in from the ground, small leaks, or rain that doesn’t drain away properly. If the air under the house is not moving well, or if warm air meets cool surfaces, moisture collects and stays there. Over time, this dampness lets mold spread on wood and other surfaces.

Consistent Moisture in Crawl Space

Most crawl spaces have bare soil floors. The soil draws moisture upward through capillary action, moving water from moist areas to dry ones. This moisture then evaporates from the surface into the air. The wetter the soil, the more vapor it releases, keeping the crawl space air constantly humid. According to the U.S. Environmental Protection Agency (EPA), this ground vapor buildup is one of the common causes of dampness and mold in crawl spaces.

Groundwater is another main source of moisture. When the water table is high, rainfall is frequent, or the ground is low, water slowly seeps through the foundation walls or cracks into the crawl space. It may not form visible puddles, but it evaporates over time, raising the humidity inside. In the long run, this “hidden seepage” makes the walls, beams, and insulation absorb moisture and encourages mold growth in your crawlspace.

Poor Ventilation

Good ventilation depends on having both intake and exhaust vents to create air flow.

When a crawl space has openings on only one side or the vents are blocked, air can’t circulate.

Moisture stays trapped inside the crawl space, and so do mold spores.

In the southeastern and coastal states of the U.S. (like Florida, Georgia, North Carolina, and Virginia), the air is very humid.

Even with vents open, the outside air brings in more moisture.

In summer, warm humid air enters the cooler crawl space and condenses on the floor above, adding more dampness.

Many homeowners end up closing or sealing the vents, which makes the ventilation even worse.

Leaks or Poor Drainage

Leaks can come from many sources, including cracked foundation walls, broken drain pipes, or downspouts that discharge water too close to the house. Once water enters and remains there, it can significantly elevate moisture levels, promoting mold growth in the crawl space.

Another major cause of mold in your crawl space is poor drainage around your home. When rainwater isn’t properly diverted away from the foundation, it can pool around the base of the house and slowly seep into the crawl space.

Hurricane or Major Flood

Large water events like hurricanes, heavy storms, or flooding can dramatically increase the risk of mold in your crawl space. Even after the visible water recedes, structural materials, like wood joists, insulation, and subflooring can remain damp for days or weeks. If these wet materials aren’t dried within 24 to 48 hours, mold spores can begin to grow and spread rapidly. According to moisture control guidance, prompt drying and remediation after heavy rain or flooding is essential to prevent long-term mold colonization.

Professional Techniques for Crawl Space Mold Removal

Seal the Crawlspace with Plastic Sheeting

Before any mold removal in a crawl space, the area must be properly isolated from the rest of the home. Disturbing mold releases large amounts of microscopic spores, which can easily spread into the living space above, enter HVAC ducts, or move from contaminated areas to clean sections of the crawl space. Professionals seal the work area with heavy-duty plastic sheeting, block all openings to interior spaces, and create negative air pressure so that air flows into the containment zone rather than escaping.

Remove Mold Spores Using HEPA Air Scrubber

Visible mold is only part of the mold problem in crawl space. Airborne and settled spores remain after cleaning, and ordinary vacuums can blow them back into the air. HEPA air scrubber capture 99.97% of particles down to 0.3 microns, removing spores, dust, and debris from wood beams, joists, subfloors, and corners. This reduces airborne spores, prevents them from resettling, and creates a clean foundation for antimicrobial treatments, making crawlspace mold removal more effective and long-lasting.

Clean Mold with Professional Antimicrobial Solutions

In crawl space remediation, professional antimicrobial solutions are essential. Mold often penetrates porous materials like wood and subflooring, where ordinary cleaners or bleach cannot reach. Antimicrobial products penetrate surfaces, destroy mold at the cellular level, and prevent regrowth. They are safer for structural materials and, by treating both visible and hidden mold, significantly reduce the risk of recurrence.

Remove Mold-Contaminated Materials

In crawl space mold remediation, removing materials that are contaminated with mold is a necessary step. Once mold has penetrated deeply into a material, it cannot be fully removed by cleaning. If these materials are left in place, they can become a source of mold returning.

Common materials that need to be removed in crawl spaces:

Water-damaged or moldy wood beams, flooring, or support lumber: Wood is porous and absorbs moisture, allowing mold to grow deep inside.
Fiberglass insulation: Holds moisture and is dense, making it hard to clean and easy for mold to thrive.
Paper or fiber-based materials:

Dry Crawl Space with Commercial Dehumidifiers

The main purpose of using a commercial dehumidifier in crawl space remediation is to stop mold from coming back after cleaning. Mold removal activities—such as brushing, HEPA vacuuming, and antimicrobial treatment—often release spores and add moisture to the space.

In a crawl space, that moisture does not dry on its own. A commercial dehumidifier actively removes moisture from the air and, more importantly, from wood framing and subfloor materials, lowering their moisture levels to a point where mold cannot grow. This drying step stabilizes the environment immediately after cleaning and prevents remaining or newly disturbed spores from reactivating.

What to Have Ready Before Mold Cleanup

Personal Protection

N95 mask
Safety goggles
Gloves (nitrile, rubber, or vinyl)
Disposable coveralls or long sleeves and pants, plus washable boots or shoe covers

Cleanup Tools

Vacuum cleaner — HEPA preferred
Thick plastic sheeting (6 mil works well) and tape
Thick, sealable trash bags
Flashlight or headlamp, stiff brush or sponge, cleaning cloths
Dish soap or general cleaner, plus a spray bottle with water
Dehumidifier, fans (optional), and a humidity meter (optional)

How to Remove Mold in Your Crawl Space (Step by Step)

The following steps will guide you to easily remove mold in your crawl space.

Step 1: Fix Any Water or Moisture Problems

Check for plumbing leaks, ground moisture, condensation, and entry points during the rainy season (foundation cracks, vents, external drainage). The EPA highlights that "moisture/water is the root cause of mold problems."

Turn off the HVAC/ventilation system (if the crawl space is connected to ducts/return air, shut it down to prevent spreading).

Step 2: Seal the Crawl Space with Plastic Barriers

Seal openings, vents, and access points with plastic sheeting. Reduce mold spores from entering the living area.

Step 3: Discard Mold-Contaminated Items

Cardboard boxes, rags, moldy insulation or fiberglass, mold-contaminated wood chips or debris, and any items with visible mold should be sealed in bags and removed from the crawl space.

Step 4: Clean Mold from Surfaces

Spray a cleaner mixed with water onto moldy areas, then scrub the mold off using a stiff-bristle brush. The key is to physically remove the mold, not just spray chemicals.

Wipe the surface repeatedly with clean cloths or paper towels, replacing them as they become dirty.

Once surfaces are completely dry, a HEPA vacuum can be used to remove remaining mold spores and dust.

Step 5: Dry the Crawl Space with a Dehumidifier

Run a dehumidifier continuously, making sure the drain hose leads outside or to a proper drain so moisture does not re-enter the space.

Use fans to improve air circulation, but avoid blowing mold dust toward indoor openings. Continue until there is no visible mold, no musty odor, and all surfaces are dry to the touch.

Crawl Space Mold Prevention and Maintenance

Preventing mold in your crawl space is key to a healthy home and lasting structural integrity. Moisture from soil, rain, and air leaks creates ideal conditions for mold. Using proper drainage, vapor barriers, sealed vents, and a crawl space dehumidifier—or full encapsulation—helps control humidity, block moisture, and reduce mold risk.

Improve Drainage

Poor drainage outside the home is a major cause to crawl space moisture. When rainwater or surface water remains near the building, it repeatedly penetrates the foundation and enters the crawl space. The key purpose of drainage improvement is to redirect water away from the foundation through proper grading, longer downspouts, and unobstructed drainage systems. Once exterior water is controlled, long-term crawl space humidity can be reduced.

Install Crawl Space Vapor Barrier

In a crawl space, the primary source of moisture is exposed soil. Ground moisture continuously evaporates upward. Installing a vapor barrier creates a physical separation between the soil and the crawl space. Only when soil evaporation is effectively blocked can crawl space humidity be controlled over the long term, making this the most basic and critical step in crawl space mold prevention.

Seal Vents & Air Leaks

Moist outdoor air can enter the crawl space through vents and gaps, where temperature differences cause condensation and promote mold growth. Sealing the vents keeps humid air out and helps the dehumidifier run efficiently.

Install Crawl Space Dehumidifier

Installing a crawl space dehumidifier keeps relative humidity at 30–50%, disrupting the moisture needed for mold growth. Argendon crawlspace dehumidifiers are built for continuous operation, with high-efficiency dehumidification, pump drainage, and reliable performance in cold, humid conditions. Ensure the drain hose directs water outside to avoid moisture returning to the space.