Bad crawl space repairs are common in our industry because there really is no standard when it comes to fixing crawl spaces. When considering crawl space repair make sure you understand that you can make things worse if you do repairs out of order or incorrectly.

DIY crawl space repair is a great way to save money when it is done correctly. For example, using a vapor barrier that eventually could smell like cat pee should be avoided. The cost to repair a crawl space can be minimal when compared to the cost to correct bad crawl space repairs.

Wet Crawl Space

A wet crawl space is common in the summer. An unusually hot summer can make a vented crawl space even worse than usual because the air conditioner is having to work harder and longer to maintain the proper temperature which may increase condensation.

When the dew point is reached in a crawl space that's when condensation occurs. Condensation can create mold growth and even damage insulation, flooring, joists and sub-floors.

Vented Crawl Space

An open or vented crawl space allows humidity to freely travel in which means the crawl space is the same humidity level inside as the relative humidity outside. Because of the HVAC air ducts, the humidity can get even worse inside the crawl space.

When that humid air hits the cold air ducts condensation occurs and will add to the already present humidity. This can cause some crawl spaces to reach more than 90% relative humidity. High humidity soaks into the fiberglass, joists, sub-floor and other porous materials and may lead to mold and wood rot fungus that can damage the home and affect your health.

1. Adding fiberglass to a humid or wet crawl space:

Fiberglass or Batt insulation is just that, glass fibers that are woven together and looks similar to wool. In a crawl space, fiberglass is normally placed between joists against the sub-floor and also shoved into the rim joists. Fiberglass can be a home for rodents and pests and will absorb water.

Fiberglass will trap water from humidity or a plumbing leak against the floor and joists. In extreme cases this trapped water can even cause hardwood floors to cup or buckle. Wet wood will eventually grow mold. Fiberglass can also become so heavy from the absorbed water that it falls out of place and your home loses its efficiency.

2. Improperly installing a sump pump:

We recently addressed a standing water problem in a crawl space where they installed a sump pump improperly. The basin did not have weep holes to allow the ground water to enter. The water had to reach the ground’s surface in order to enter the basin.

Also, the pump was too big for the basin and kept tipping over so it would not turn on without the homeowner having to constantly intervene. The discharge hose did not have a check valve installed so when the water was pumped out it would back flow into the basin after the pump shut off and this caused the pump to run more than necessary.

And lastly, the crawl space had standing water throughout and that water had no clear path to reach the basin and sump pump. Properly trenching the perimeter of the crawl space would have corrected that issue and given the standing water a path to the sump pump. It’s a good idea to install a water alarm to alert you immediately of any standing water or flooding that could occur in your crawl space.

3. Encapsulating the crawl space without a dehumidifier:

Crawl space encapsulation seems to be the preferred method for controlling moisture. Many homeowners will perform crawl space encapsulation but then choose not to install a dehumidifier.

Many times the dehumidifier may be sized incorrectly or drained improperly. Draining the dehumidifier directly out of the crawl space or into a sump pump basin is a great option that seems to produce less problems. Draining the dehumidifier under the vapor barrier can increase the humidity because moisture can eventually evaporate from under the plastic.

Another option is to install a remote humidity reader so you can keep close tabs on the relative humidity of your crawl space and make sure the dehumidifier is working properly. Make sure you check the dehumidifier every few months to ensure filters are clean and all parts are working properly. The dehumidifier is the heart of a healthy crawl space encapsulation system.

4. Crawl space encapsulation without proper ventilation:

Radon and soil gases can build up in a closed or improperly encapsulated crawl space. Soil gases can be from contaminated water or soil in your area. The Environmental Protection Agency has more information about “Soil Vapor” on their website

Radon is a soil gas most people are familiar with and it is caused from decayed uranium found in the soil under your home. An open or vented crawl space allows soil gases to exit the home regularly but when that crawl space is closed or encapsulated, the gases or vapor has nowhere to go except up into your living space.

Properly installing an active ventilation system or sub-membrane radon mitigation system is recommended by the EPA in all closed crawl spaces. This will add other benefits to the properly insulated crawl space and make your home even more efficient.

5. Using gravel to cover the crawl space floor versus a vapor barrier:

We sometimes get asked if we can install gravel on the crawl space floor to stop moisture from evaporating from the soil. The answer is “yes” we can install the gravel but “no” it won’t stop moisture from evaporating.

Gravel on the crawl space floor does little to help the crawl space at all and makes it hard to work in. It can also puncture the vapor barrier which will allow humidity to escape more rapidly into the crawl space and make the dehumidifier run more which will increase your utility bill.

Gravel can allow water to channel under the vapor barrier but it is not the best solution available. There are better alternatives to gravel if you want to channel water under the vapor barrier.

6. Spray foaming the entire sub-floor:

Spray foam insulation is great when used properly. We utilize spray foam on almost every job to air seal the crawl space. When spray foam is used properly, the Department of Energy says it may save up to 19% on your utility bills.

Applying spray foam to the entire sub-floor is a great idea if you never have a water leak from above. If a pipe ever starts to leak, that water can become trapped just like it would with fiberglass insulation. Trapped water leads to all sorts of damage.

7. Installing a vapor barrier to the joists/sub-floor:

We have ripped out many thousands of square feet of plastic that was installed (stapled) to the joists in a crawl space or unfinished basement. Moisture gets trapped between the plastic, insulation and sub-floor and has no way to escape.

Installing a vapor barrier properly on the ground and possibly walls of a crawl space should be sufficient to control moisture with the addition of a properly sized and installed dehumidifier.

8. Fixing a sagging floor before addressing the mold:

Sometimes moisture, mold or wood destroying fungus can be the cause of floor issues and foundation problems. If your home has sagging floors you should consider having the wood treated for mold and apply a mold preventative as well as address the moisture problem before fixing the floors or foundation.

It is much more difficult and costly to address the mold and water issue after because many times new wood is used and pressed against the moldy damaged wood. This sandwiches the mold between new and old wood. The mold will attack the new wood and given enough time can damage it to the point of needing repair as well.

9. Adding more foundation vents or power vents:

The Southern United States, especially Tennessee, is very humid so adding more vents or fans to a crawl space in order to draw outside air in may do more harm than good.

Their should be measures in place to control humidity and bringing outside air into a crawl space is not controlled. An open or vented crawl space is at the same humidity level as the air outside so if you have a few weeks or months at high humidity outside, the same is true for your crawl space.

10. Insulating the walls of an open/vented crawl space:

If you choose to leave your crawl space vented or open then one of the best ways to insulate it is with fiberglass installed between the joists and against the sub-floor. Applying foam board insulation to an open crawl space does not help in keeping the cold or heat from entering the crawl space because the vents allow the outside temperature to freely enter.

This can make the floors colder in the winter and may cause a flood if the pipes are not properly insulated. Only insulate the walls if you decide to close the crawl space. I know this totally contradicts #1 above but if you are going to keep your crawl space open, it must be insulated and in an open crawl space fiberglass is the best alternative.

Just make sure you inspect the humidity of your crawl space on a regular basis and look for falling fiberglass insulation. If you appear to have strips of fiberglass dangling down like stalactites, this is an indication of a humidity or other moisture problem.

Bonus Tip:

Another repair to consider is upgrading your HVAC system but keeping the same ducts and duct insulation. If you have a ten plus year old home, the insulation R value of your air ducts may need to be upgraded or the ducts themselves may need to be replaced or air sealed for maximum efficiency.

Consider this expense when upgrading your HVAC system because improperly insulated or poorly sealed air ducts are more likely to condensate with a more powerful HVAC system. Some estimate that up to 25% of your conditioned air can be lost in the crawl space due to improper sealing and inadequate insulation of the air ducts

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Contact us if you need help fixing your crawl spacebasementatticduct-work, or yard drainage by clicking here.

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About Michael Church

Michael Church has been involved with indoor air quality since 2005 and feels the unhealthy crawl space is one of the major problems causing poor indoor air quality.


  1. Jenkins Leroyson on November 17, 2015 at 4:56 pm

    We had a similar situation with our sump pump once. We had to learn the hard way that improperly installing it can cause a lot of issues. I like your tip about installing a water alarm since that’ll help minimize any problems you could have. Thanks for sharing this.

    • Michael Church on November 20, 2015 at 1:32 pm

      Thank you so much for sharing about your situation. Sump pumps are very important to the health of crawl spaces and basement waterproofing.

  2. Dean on December 11, 2015 at 10:51 pm

    Thanks for addressing these issues. I like to do regular preventative maintenance and inspections to ensure that no major issues pop up. This list will help me continue to do a better job. Thanks

  3. Termites, Termite Control in Crawl Spaces Step 1 on February 10, 2016 at 9:22 pm

    […] High humidity in a basement or crawl space is one way to attract termites. Termite colonies prefer a moist environment and high humidity will be absorbed by wood. Wood moisture levels are always high in a humid environment. Having a good dehumidifier installed in your crawl space is a great way to control humidity which in turn can keep wood dry. The Santa Fe Brand of dehumidifiers is our preferred way to control humidity in a crawl space or basement. […]

  4. Rachel Finn on February 19, 2016 at 5:59 pm

    I had no idea that closing off a crawl space could lead to problems with gasses. We are wanting to close the crawl space in our basement because it seems to let all the warm air out during the winter. I will have to do a lot of research and make sure we are doing it correctly so that we stay safe. Thanks for the tips!

  5. Crawl Space Encapsulation - Don't Do This! on April 27, 2016 at 8:31 pm

    […] you would like more information please feel free to read another article on 10 Bad Crawl Space Repairs. Some of the information may overlap but it has more details you may […]

  6. Braden Bills on May 17, 2016 at 1:54 pm

    I think it’s important to make sure that you have your crawl space repaired correctly. There are a lot of ways that you can mess it up if you do it on your own. I feel like you would get the job done and save money by hiring a professional. Thanks for sharing!

    • Michael Church on May 17, 2016 at 8:14 pm

      I agree Braden. Sometimes you can make the problem worse if you don’t know what you are doing.

  7. […] you considered installing a french drain pipe (curtain drain) in order to divert water from your crawl space or basement? Sometimes the task can be quite difficult and if you are going to perform this project […]

  8. Vented Crawl Space | Crawl Space Repair on May 19, 2016 at 6:54 pm

    […] not be aware of how our humid climate can affect their crawl space. Homes up for sale will uncover crawl space problems during the home inspection process but even some home inspectors are unsure how to advise […]

  9. […] we are there to perform mold removal. Termites and mold seem to thrive in the same conditions. Wet crawl spaces or water damaged basements are great places to find mold and termites. Another time to be aware of […]

  10. […] is the best way to detect hidden mold. Hidden molds can be trapped behind walls and insulation. Crawl space mold is a problem for many sellers of homes. Unfortunately, many mold removal contractors fail to […]

  11. Jane Hinds on November 23, 2016 at 10:08 am

    Helpful, thank you, but more questions, if you will please-
    I just purchased a small house with serious mold in the crawl space, and treated it with bleach solutions (two to one) also vinegar (same) threw on baking soda. Even the inch long molds in some areas are now dry and flat. The worst was near an HVAC small leak. The crawl space dirt floor is almost 100% sandy dry dirt. The space has several modest openings to the outside “cracks” around various pipes. I do run two dehumidifiers which presently depend on my emptying them- a real chore for me since I am just shy of 80.
    Since the mostly standing height crawl 24×36 foot space has three somewhat level plateaus I want to bring in several yards of 89-10 gravel to level one or two of the plateaus and place a very heavy plastic over the entire space so I can use the area for dry storage of tools and plastic binned storage. Since there appears to be no ground water will this be adequate?
    Your experienced comments would be very much appreciated.

    • Michael Church on November 23, 2016 at 2:10 pm

      Hi Jane. Thank you so much for contacting us. It sounds like you are on the right track if there is no standing water. Just make sure you use a good vapor barrier and perhaps even an underlayment if you are using the space for storage. Gravel can be somewhat rough on cheap vapor barriers. Here is some information on the one we recommend:

  12. […] you would like more information please feel free to read another article on 10 Bad Crawl Space Repairs. Some of the information may overlap but it has more details you may […]

  13. Ivy Baker on March 10, 2017 at 11:55 pm

    I like that you talked about how you should insulate your crawl space. I like that you pointed out that you should do this to help prevent your pipes from freezing. It does seem like I would also help your AC unit from having to work as hard to keep your home cool or warm.

  14. […] 10 Bad Crawl Space Repairs You Should Avoid […]

  15. P. D. Miller on January 22, 2018 at 5:27 pm

    Have water seeping thru concrete block foundation making water stand in my crawl space. Also have mold on cross beams. Have had two estimates to repair. One is to encapsulate. The other is to use B Dry system and use a trench, sump pump, and dehumidifier. I plan on selling my house after making repairs. I was told that house imspectors don’t like ensapsulation because they need to see foundation. What should I do.

  16. Pam on March 3, 2018 at 9:54 pm

    Have a spray foam closed crawl space and water appearing on top of 6ml vapor barrier. One contractor suggesting dehumidifier connected to pump piped to existing exterior frecch drain and adding thicker vapor barrier. Other contractor wants to do interior trench and sump pump and dehumidifier and thicker vapor barrier at 5 times cost How do we know which is correct choice?

    • Michael Church on March 5, 2018 at 9:08 am

      Hello, Great questions. If it is determined the water on the plastic is coming from ground or foundation walls, you may want to consider the trench pump, new plastic and dehu. Keep in mind I am not telling you to do that but if you only do dehu and new plastic that does not solve the ground/foundation wall problem. Sometimes the 3rd opinion from a local contractor can shed some light on things as well. Good luck.

  17. Kayla on March 8, 2018 at 2:46 am

    I didn’t know that bad crawl space repairs are common in our industry because there really is no standard when it comes to fixing crawl spaces. The air inside the house feels stuffy and dusty. My dad suggested hiring contractors for crawl space repair and shared this article with us.

  18. Chrissy Buckley on March 22, 2018 at 8:40 pm

    I have been watching your videos and trying to learn what to do on my crawl space. I am a single mom and do not want to get ripped off. My crawl space does not hold water but has tons of condensation from living here in Arkansas. I am trying to decide which company to use as they have vastly different ideas!! In your opinion…1. No sump pump if I only have humidity water and no flooding or standing water? 2. Fully inclosed I am be needing a dehumidifier because it cant be good to incase it all with out one due to gasses and needing to get the moisture out. 3. The machine will be what takes my radon out from under there is what I’m reading, right? 4. What is a good remote humidifier gage brand you like? Thanks so much for your advice. Wish you lived close… I would hire you in a hurry !!

  19. Jennifer on July 3, 2018 at 1:52 pm

    This was helpful! We recently discovered fungus in our crawlspace and high moisture. We have received a wide range of solutions from removing encapsulated insulation and putting in fans to encapsulating with a dehumidifier. We just want to make the right decision that will benefit our home and be the best financial situation.

  20. matthew on August 6, 2018 at 9:39 am

    I just had an encapulation done and the contractor put in vapor barrier on the wall but left 3 layers of brick exposed. Why not go from floor to rim joist? The vapor barrier was nailed to the crawspace wall (concrete block) and not taped at top. This will just let air through and keep humidity high even with a dehumidifyer. The rim joist were spray foamed but i think too much air will be let in. Should i put in more vapor barrier to the joist to seal it completely or is there a reason this should be left open?

    • Michael Church on August 11, 2018 at 9:52 am

      If you have termites in your area they may have left the gap so that your termite company could see termite tunnels. this is according to code. Also there is a debate whether sealing up plastic to the block could cause harm to the block or not. depending on what the contractor believes they may have left it exposed so that moisture could escape in order to keep the block from keeping moisture in it. Here is a video about termite gaps.

  21. Stephen Kaufman on September 15, 2018 at 2:16 pm

    We live in central Illinois and are considering addressing humidity and mold problems in our crawl space by encapsulation and using a high efficiency dehumidifier with drainage to a sump pump. Although this approach has some attractions, given our situation it also comes with its own issues. One has to do with the fact that our gas furnace and gas water heater are located in the crawl space. Given this, sealing off air inflow from outside may prove problematic. It is not clear to me whether “leakage” from duct work, etc., would provide sufficient airflow,whether installation of vents from the crawl space to the first floor of our house would do the job, or some other solution. Also, how does one achieve proper outflow ventilation of possible radon and soil gases in this situation? Basically, how can proper ventilation be achieved in an encapsulated crawl space that has combustible appliances? Or, is non-encapsulation or a separate HVAC system for the crawl space, or something else a better solution under these circumstances. Thanks. Would appreciate an email response as well.

    • Michael Church on September 19, 2018 at 9:04 am

      Hello, great question. In TN if you encapsulate your crawl space according to local code inspectors 1 CFM of air for every 50 square feet of crawl space is sufficient. But…… you should check local codes enforcement or home inspector or HVAC company to see what your requirement is. Hope that helps.

  22. […] 10 Bad Crawl Space Repairs You Should Avoid […]

  23. BetsyL on April 25, 2019 at 6:13 pm

    I have a crawl space that’s only 12-inches high. I already have two sump pumps, and I want to install encapsulation and a dehumidifier, but contractors are telling me I have to remove the floor of my finished basement to gain access because 12-inches isn’t enough access space. I’m considering just putting in a compact dehumidifier (like the Santa Fe Compact70 Dehumidifier) without encapsulation. I assume that if we install a dehumidifier without encapsulation, there will be more moisture for the dehumidifier to remove, so it will run more, increasing our utility bill. That would still be a lot cheaper than tearing up the interior floor and rebuilding! What do you think about our situation?

    • Pedro Mendoza on April 26, 2019 at 8:28 am

      Thanks for reaching out, given the size of the crawl space yes you would have to pull up the floor in order to encapsulate. Regarding adding the dehumidifier in as it is, yes it will run more often because there will be more humidity; We would price out what it would cost for a rebuild and try to assign a value on how much your utilities would go up per month and go from there. Hopefully that helps! let us know how it turns out and we are here to help!

  24. Rick Jonie on October 7, 2019 at 9:18 pm

    I’ve got vents in my crawl space and have heard nothing but bad things. I’m wanting to cover over them, my question is…should I just fully encapsulate while I’m there, or wait it out and see if that takes care is the issue?

  25. Darci Thompson on January 29, 2020 at 11:06 am

    What about a layer of pea gravel under a good grade of poly?? wouldn’t that help prevent punctures, yet aid in draining and keeping water from creating “soup” under the poly?

    • Michael Church on January 29, 2020 at 11:22 am

      Absolutely, any smooth stone will work great. Thanks for sharing.

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