How to Solve Moisture Problems Under Your Home

We live in an older home that is raised a couple of feet off the ground with a crawlspace under it. In the past few years, the hardwood flooring in several rooms has started to warp and cup. What could be the problem?-Mary

Hi Mary,

It sounds like you may have excessive moisture and humidity in the crawlspace under your home. Here’s what you can do to correct it:

  • Make sure the ground around your foundation slopes away from the house (1/2″ per foot or more).
  • Divert rainwater run-off from the roof away from the foundation by installing gutters and extending the downspouts so water is diverted beyond the planting beds and out into the yard.
  • Check your air conditioner unit to be sure the AC drain pipe isn’t clogged and extend it if needed to direct condensation water away from the foundation of your home.
  • Inspect the crawlspace under your home. While the soil may be moist, it shouldn’t be saturated or have standing water.
  • Look for any plumbing leaks as well as excessive dampness, mold, and mildew.
  • If mold or mildew are present on the joists or bottom of the subfloor, treat under the house with a product such as Wet and Forget
  • Clean out any debris and stored items under your house, and fill in any holes or depressions.
  • Cover the entire crawlspace with thick, black plastic sheeting (6 mil or higher). Overlap the seams by a foot or more and run the plastic up the sides of the foundation.
  • For extreme moisture problems, consider taping the seams in the plastic together, block the outside vents, and install a dehumidifier in the crawlspace to remove excess moisture from the air.

Good luck with your project,


Further Information


  1. One effective way to combat moisture is by the use of desiccants like Silica Gel. These are the same small sachets you find in packaging of various products like electronics, garments, etc. Silica Gel works by absorbing the moisture in its surrounding area. For most moisture challenges, does the job. With small sachets cost less than a dollar, it truly is a cost effective way of protection from moisture.

  2. I am having problems with excessive condensation under my home. It is causing mold/mildew underneath my house. The insulation is all wet (I have had this removed). Some of my floors are now bulkling/swelling and in one room, the sheet rock is wet. I have had 2 air-conditioning repairmen come to check my AC unit and they are unable to find anything. I have had a contractor come & check for any leaks, pipes or roof leaks and none are visible. Insurance adjuster has come and says this is condensation but no one is able to find out where it is coming from. This has all happened or at least shown up in the last 2 months. I had renovations done 2 months ago and none of this was present then and it was dry underneath my home. Even though I am planning on getting treatment for the mold and getting new insulation, I still do not know where the problem is. How can I find out-who do I contact for this? I have also asked for a home inspector to come but they don’t handle this type of problem either from what they tell me. I am desperate to find a solution. My house seems to be deteriorating and there isn’t anything I can do to prevent it. Please help.


  4. We have a crawlspace under a small section of our home. Unfortunately, my sewing room, which I’m in a lot, is located just on the other side of the poured wall. I can smell a musty smell and am having bronchial infections now. We have put a thick layer of black plastic over the ground several years ago, but still can smell something, and I’m still having bronchial infections when I sew very much. HELP!

  5. We have an old family home that is built very close to the ground. Occasionally, mold appears in different places inside the house. When it rains a lot, the house smells and feels damp. We have some moisture barriers in the house to absorb some of the moisture. What can we do to eliminate/reduce the moisture in the house?

  6. One effective way to combat moisture is by the use of desiccants like Silica Gel. We have some moisture barriers in the house to absorb some of the moisture. I can smell a musty smell and am having bronchial infections now.

  7. Hi Danny,

    Thanks for the great advice!

    Any tips for someone who has a house that’s on a steepish hill, as it’s not very practical to make a slope away from foundations 🙁

  8. My father in laws house has lots of moisture and I think mold. He is fighting cancer and want to know who I can call locally to come check the air quality in his home?

  9. Can you tell me what kind of business you call to divert rainwater and slope the ground away from the house? I have excessive moisture in a ranch with a slab.

  10. My floors pop real bad and you can hear it run across into other rooms and my carpet is starting roll up in my bedrooms. I do not have mold or mildew under my house. Will moisture cause this or do I have a bigger problem?

  11. Hi,

    I’ve had a tree next to the house removed and now the house is cracking and doors jamming. Understand it could be moisture returning to the soil. What can I do to dry up the soil under the house? Since I can’t unremove that tree now!!

  12. I think i have a moisture problem under my crawl space I went into my closet to get a pair of shoes and found that mildew or mold is growing all over them I searched closet for moisture leaks ect nothing …..who am i to call in a situation like this I need help….1st time home buyer

  13. We have a moisture problem in our foundation. This is a newly constructed home and they applied a moisture barrier when the foundation was poured. We did the acid stain floors and it started turning milky and bubbling. That is when we found the moisture problem. We did the test and it came out with a 13.2 and13.6 moisture. We were told that this is excessive. Is there a way to correct this?

  14. i have two vent fans planed in foundation to remove moisture from under home. what percent of humidity do i need to achieve. i have humidistat set on 55%.

  15. Do you think moisture barriers under the house are a good or bad thing or does it depend on certain factors? I have heard mixed opinion as to whether they actually draw and attract a moisture problem as opposed to prevent it.

  16. I have 4ft + of crawl space live in Florida and have bad rainy summer. Crawl fills with water and now subfloor is rotting and worried man made floor joists are also moldy tried to swayl yard but water stays for awile as yard is flat

  17. My house was built on top of a concrete slab above it with piers. A crawl space of 26″ the plywood has rotten through in one room there. Is brown mold present under most of the house mostly the middle. Need to know how to prevent the rest of the house from rotting and I had never insulated the floor.

  18. What kind of monitor do I need to put one part under my crawl space
    and one part in my house .Do I need a monitor for humidity,moisture
    or what to let me know whats going on under my crawl space. One
    person told me i needed a moisture meter and the moisture contents
    should not be over 16%. Another man said I needed humidity monitor.

    Need Help
    Clarence Mills

  19. Have a new home moisture under home. Floors popping up subfloor damp with mold. Vents installed per code. No leaks in home. Can’t determine what is causing dampness under home. Need to replace floors but don’t want to until problem is solved. Can you recommend who to call.

  20. Hello. I live in an old trailer. I think it was an office for the storage units that are also on the same property. There were big gaps the way around the whole trailer almost a quarter inch. I have done my best to seal them up Now I have a bad moisture problem in here. I rent and live in Missouri. Landlords are not to quick at getting anything done they just want the rent. The.under pinning is terrible it’s busted up in some spots. I can’t afford to do much of anything that’s costly. Any suggestions? Mold is growing in my bedroom now bad. I’ve sprayed peroxide on it to kill it. Wanted to post pics but don’t see where I can do that.

  21. We have a moisture problem and MOLD in our crawl space there is plastic down and stafoam on the blocks what can we do? plus plenty of vents

    • Hi, Myra,
      Danny says, “Make sure no water is seeping into the crawlspace when it rains and consider putting a small exhaust fan mounted inside of your vents with a humidistat control. Good luck!”

  22. Dear sir,
    We have 2 bedroom unit on ground floor in Dee Why. There is dumpness in two rooms on each side of the bathroom.
    Please call me.
    Thank you,
    Paul Chernishov

    • Hi, Paul, features home improvement advice from the nationally syndicated TV show “Today’s Homeowner” and its experts.
      We can’t place individual phone calls, but would be happy to direct you to our online resources.
      Please elaborate on the issue so we can further assist you.

  23. From heavy rains in our area and poor drainage I currently have standing water in the crawl space under my pier and beam home.

    What is the best way to dry it out. We tried a small submergeabe pump but it clogged after a short time. I’m told lime can be used but am concerned about safely using it.

  24. I own a home in a retirement community. when it rains water flows ata will on both sides of my home and flooding the back .. sump pump runs for days after rain. I ‘ve wrote the board to take action , no action

  25. In 2017, I had a split system installed in my home by a A/C contractor. One of the copper insulated lines sweated so bad under my house that puddles of water formed. The contractor covered the line with heavy black plastic only for the moisture to form on top. Mildew grew on joists, my hardwood floors buckled. My question is did this line sweating cause my floors to buckle

    • Hi, Timothy,
      Great question! We have forwarded it to the Today’s Homeowner Radio Show’s producer.
      He will contact you soon to discuss featuring it during an upcoming show.
      Take care!


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