Crawl Space Mold: Warning Signs, Damage and Removal Tips

Written By Adam Paul - Waterproofing Expert

Crawlspace mold is a fungal growth that thrives in the dark, damp, and poorly ventilated environment in the crawlspace. Mold in the crawlspace decays the structure, decreases the air quality in the home, increases the health impacts, reduces the property values, and decreases the energy efficiency in the home. You can observe the mold in the crawlspace by musty odor, discolorations on floor joints, warped and decayed wood, and mold and mildew growth.

The 6 reasons for the crawlspace mold are poor ventilation, plumbing leaks, ground moisture seepage, higher humidity, standing water, and organic materials in the crawlspace. Crawlspace mold can damage the crawlspace by rotting the wood, staining the foundation blocks, damaging the insulation, reducing the air quality, increasing respiratory issues, increasing the pest infestation, and reducing the property value.

To remove the mold in the crawlspace, you should follow the expert steps mentioned below. In order to get rid of crawlspace mold successfully, you should waterproof the crawlspace, use mold and stain remover, install a crawlspace dehumidifier, and treat surfaces with sulfur and UV lights. For the severe mold colonies, you should hire a professional expert.

More than that, frequent crawlspace flooding causes crawlspace mold and musty odors. In order to control it, you can use a dehumidifier. If you do not perform mold remediation in the crawlspace on time, it will be a huge problem, even if it affects you badly when you are going to sell it. So, as waterproofing experts, we highly recommend that you follow proper steps and DIY methods to eliminate the mold from the crawlspace.

What is Crawlspace Mold?

Crawlspace mold is a fungal growth that thrives in the dark, damp, and poorly ventilated environment in the crawlspace. Crawlspace mold typically forms on wood joists, subfloor insulation, foundation blocks, and dirt surfaces. Crawlspace mold occurs due to foundation cracks, open vents, plumbing leaks, or higher humidity (above 60% RH).

There are five major disadvantages of crawlspace mold.

1. Structural decay: Crawlspace mold degrades wood beams and joists, weakening the home’s structural integrity.
2. Decrease the air quality in the home: Crawlspace mold releases airborne mycotoxins that circulate into living spaces, causing respiratory problems.
3. Increase the Health impacts: Mold in a crawlspace makes you sick, especially triggering asthma, sinus infections, and chronic fatigue.
4. Reduce the property values: Mold in crawlspace lowers resale value due to remediation costs and health concerns.
5. Decrease the energy inefficiency: Crawlspace mold-infested insulation loses effectiveness, leading to higher HVAC costs.

What are the 5 Signs of Crawlspace Mold?

Detecting crawlspace mold early is critical for preventing costly structural damage and health hazards. When you inspect the crawlspace, you can observe the following 5 signs. Those are the strong mold indicators in the crawlspace.

1. Musty odor in the home: Crawlspace mold releases microbial volatile organic compounds (mVOCs), causing a damp, earthy smell that seeps into living areas.
2. Discoloration on floor joists or insulation: Black mold in the crawlspace and thick white mold in the crawlspace often appear as dark or fuzzy patches on wood, ductwork, or fiberglass.
3. Warped wood or decayed framing: Mold retains moisture against materials, leading to softened or buckling floor supports.
4. Increased allergy symptoms indoors: Mold in a crawlspace makes you sick by triggering sneezing, coughing, or headaches when spores enter HVAC systems.
5. Visible mold on foundation blocks: Mold on foundation blocks in the crawlspace shows as speckled growth along concrete walls and often requires specialized mold and stain remover treatments.

What are the 6 Reasons for Crawlspace Mold?

The 6 reasons for the crawlspace mold are poor ventilation, plumbing leaks, ground moisture seepage, higher humidity, standing water, and organic materials in the crawlspace.

1. Poor ventilation: A poorly ventilated crawlspace causes mold due to no airflow, trapping humidity and allowing condensation to settle on wood and insulation.
2. Plumbing leaks: Plumbing leaks in the crawlspace saturate surrounding materials and fuel mold, especially in crawlspaces with untreated wood or dirt flooring.
3. Ground moisture seepage: Ground moisture seepage increases dampness in the crawlspace, which is the main factor of mold growth.
4. High humidity levels: Higher humidity levels thrive mold when it stays above 60% without a dehumidifier or proper drainage system in the crawlspace.
5. Flooding or standing water: Flooding or standing water in the crawlspace accumulates water after heavy rain or sump pump failure. It causes mold to thrive in the crawlspace.
6. Organic material buildup: Organic materials like dust, dead insects, wood scraps, and insulation debris all provide food for mold types in crawlspace environments.

What are 7 Damages of Crawlspace Mold?

Crawlspace mold damages both human health condition can building conditions. So these are the 7 damages of crawlspace mold for both humans and the structure.

1. Structural wood rotting: Mold deteriorates subfloor joists, sill plates, and beams by breaking down cellulose, leading to sagging floors and structural instability in the crawlspace.
2. Foundation block staining: Mold on foundation blocks in crawlspace leaves black, green, or white streaks that indicate trapped moisture and potential efflorescence.
3. Insulation damage: Moldy insulation loses R-value, absorbs moisture, and becomes a breeding ground for mildew and bacteria in the crawlspace.
4. Ductwork contamination: Mold spores infiltrate HVAC systems, reducing indoor air quality and circulating allergens throughout the home.
5. Respiratory health issues: Mold in a crawlspace makes you sick by aggravating asthma, allergies, and chronic sinus infections.
6. Pest infestation: Damp, moldy crawlspaces attract termites, cockroaches, and rodents, compounding the damage.
7. Reduce the property value: Homes with visible black mold in the crawlspace often appraise lower due to the cost of mold remediation and health concerns for potential buyers.

How to Remove Crawlspace Mold?

To remove crawlspace mold you should follow the below 7 step by step guide.

1. Inspect and identify mold types: Determine the extent of contamination and mold types in the crawlspace using visual cues and moisture meters.
2. Wear proper safety gear: Always use gloves, N95 respirators, and coveralls to protect against airborne spores and chemical exposure.
3. Dry the crawlspace thoroughly: Use crawlspace exhaust fans and dehumidifiers to bring the humidity below 50% RH before cleaning the crawlspace.
4. Remove contaminated insulation and debris: Discard moldy fiberglass, vapor barriers, and organic materials that can’t be restored in the crawlspace.
5. Apply mold and stain remover: Use professional-grade solutions like liquid zinc, sulfur for crawlspace mold, or enzymatic cleaners on joists, subfloors, and block walls for crawlspace mold.
6. Scrub or sand affected surfaces: Use wire brushes or sanding tools to physically remove embedded spores in wood in the crawlspace.
7. Apply fungicidal sealant: Seal treated surfaces with anti-mold coating to prevent regrowth and improve resistance to moisture in the crawlspace.

How to Get Rid of Crawlspace Mold?

Getting rid of crawlspace mold effectively requires combining waterproofing and mold treatment methods. So you should follow the below 5 methods to get rid of crawlspace mold.

1. Waterproof the crawlspace: Seal foundation walls, apply vapor barriers, and install interior French drains or sump pumps to prevent ground moisture and water seepage in the crawlspace. Without waterproofing, mold treatment for dirt in crawlspace or foundation blocks won’t last.
2. Use mold and stain remover: DIY homeowners can apply commercial-grade products such as liquid zinc or botanical solutions to treat mold on wood, blocks, and insulation surfaces in the crawlspace.
3. Install a crawlspace dehumidifier: Maintain relative humidity below 50% using a high-capacity dehumidifier to stop mold spores from regenerating in humid conditions in crawlspace.
4. Treat surfaces with UV light or sulfur: Professionals use a UV lamp for moldy crawlspace and sulfur for crawlspace mold to kill spores at the molecular level without harmful residues.
5. Hire professional mold remediation experts: For thick white mold in crawlspace or black mold colonies, certified crews like Aqviz perform advanced crawlspace mold remediation, including media blasting, sealing, and post-treatment testing.

What are the 5 Reasons for Crawlspace Flooding?

The 5 reasons for the cralwspace flooding are,

1. Improper exterior grading
2. Broken or leaking plumbing lines
3. Clogged or missing gutter downspouts
4. High groundwater table without a sump system
5. Cracks or gaps in the foundation walls and footings

What is a Musty Crawlspace?

A musty crawlspace is an underfloor area of a building that has developed a stale, damp, or moldy odor due to high moisture levels, poor ventilation, or microbial growth. Musty odor occurs around foundation walls, plumbing penetrations, and crawlspace corners where water and humidity often linger in the crawlspace.

Will a Dehumidifier Kill Existing Mold under the Crawlspace?

No, a dehumidifier will not kill any mold under the crawlspace. A dehumidifier is not a mold killer. A dehumidifier is a humidity-controlled equipment. It can maintain a certain humidity level in the crawlspace. You should install a dehumidifier in the crawlspace after its mold is cleaned. The dehumidifier can control the humidity in the crawlspace and prevent it in the area.

Will a House with a Moldy Crawlspace Sell?

Yes, a house with a moldy crawlspace can sell, but not without consequences, typically a lower sale price, longer time on the market, or required remediation before selling. As real estate professionals often consult us at Aqviz, we’ve seen mold issues raise red flags during inspections. Buyers, lenders, and home inspectors treat crawlspace mold, especially black mold in the crawlspace or thick white mold in the crawlspace, as serious defects due to potential structural damage and health risks during selling it.

Does Crawlspace Encapsulation Cause Mold?

Crawlspace encapsulation itself does not cause mold; rather, it prevents mold growth when installed correctly. At Aqviz, we emphasize that proper encapsulation involves sealing foundation walls and floors with high-quality vapor barriers, combined with moisture control measures. When done right, encapsulation eliminates humidity and water intrusion that cause crawlspace mold.

How to Reduce Mold in DIY?

Reducing crawlspace mold through DIY methods requires consistent moisture control and cleaning efforts. You can follow these 5 ways to reduce mold in DIY.

1. Install a vapor barrier in the crawlspace
2. Improve drainage around the foundation
3. Fix plumbing leaks near the crawlspace
4. Increase crawlspace ventilation
5. Clean crawlspace mold spots with appropriate removers

Will Ozone Kill mold in a Crawlspace?

Yes, Ozone can kill some surface mold spores in a crawlspace, but it is not a reliable or complete solution for crawlspace mold removal. At Aqviz, we have found that while ozone generators may temporarily reduce airborne mold spores, they cannot reach mold growing deep within wood, insulation, or foundation materials. Mold colonies embedded in these surfaces require physical removal and chemical treatment to fully eradicate.