How to Reduce Mold and Moisture Under Your Home

Man with headlamp inspecting crawlspace under house.
Allen Lyle inspecting crawlspace under house.

The crawlspace under your home can be a breeding ground for mold. Taking the following steps can keep it from happening:

  • Make sure the crawlspace has plenty of ventilation.
  • Fill in any low spots in the crawlspace with sand.
  • Cover the ground under the entire crawlspace with a layer of 6 mil or thicker plastic.
  • Put a layer of sand on top of the plastic to hold the plastic in place and absorb any excess moisture.

Further Information


  1. Another solution would be to install heavy 20 mil plastic up the wall, fasten and seal it to the top of the foundation. Run the plastic along the ground and seal every seam that overlaps the ground and wall with tape. Then seal your vents and condition the space with existing HVAC or from the upstairs air. This will convert your crawlspace into a clean, healthy environment. If standing water is a problem, a drainage system may be needed prior to installation.

  2. Great video. Another solution would be to install heavy plastic in your crawl space, and encapsulate to ensure that your sealing off unwanted moisture.

  3. I own a 50s house that has been extensively remodeled to include insulation in the rafters, knee walls in up stairs attic area and in between first and second floor.. We are experiencing high humidity issues (80 plus). The house is well insulated with the exception of the down stairs floors. In inspecting the under area, it has mold growing on the floor joist and sub floor. The under area is damp where the mold is growing but no signs of moisture. I am increasing the ventilation (leaving vents and access holes open) and plan to put down plastic. Question: Should I add insulation under the floor and treat the under floor area for mold?

  4. There is a section under our house that has standing water that looks stagnant and has white mold on top of it.
    Is this safe? Willnit cause health issues?
    And what do we do?

  5. Hi my husband and I bought a house in September we moved in November. On November 22nd..i started to develop some kind of allergy. I have been going to an allergist ever since. Some days I woke up with swollen eyes, lips and bumps all over my body. Unfortunately, an inspector came and found mold in the basement ceiling. I have2 crawled spaces…they told me there’s a lot of moisture in the basement wall. The big mistake was we didn’t do a home inspection so we can’t go after the seller which is a BANK. We are broke we have been borrowing money from people to do work on the house. A remidiator came and clean the mold. Now he said we have to buy a dehumidifier for $2000.00 otherwise the mold will return. We are in desperate need for help…please help if you can.

  6. Hi my house smells like pee when it rains we don’t have any pets we believe it’s coming from under the house could it be due to the mould??

  7. I have a question my house is built that way to it’s it’s exactly the same way as the picture that you are showing has no insulation under it a toll would that cause mold in my house

  8. . We have mold coming into two bedrooms up stairs thru the light switch covers. Down stairs everything seems clear. Thought we had it stopped by insalating more tightly from roof side. Into the ceilings. Walls are 5 years old. Hvac supply ducts Are under that roof, we have a sumb pump under house and house is well insulated. Going to get a hygrometer to measure humidity. Hvac people have come, insulation people have come, no one knows what’s happening. Help!!!!

  9. We put on a sun porch and completely enclose the area around the bottom. The top has floor slats that are open a little. Our intake air from the furnace is under this porch. Could this be collecting mold and coming in our house. I am constantly getting bronchitis and running nose. Thank you

  10. My rental in a 100 year old building has a 2 foot crawl space where crickets were making a home. The landlord had the space bombed and sealed up. Should I and the other tenant now be concerned about mold?


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