10 Bad Crawl Space Repairs

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 Spaces are Common

A wet crawl space is common in the summer due to high humidity and dew point. 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 Spaces Can Cause Moisture Problems

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.

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10 Terrible Crawl Space Repair Examples


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

One bad crawl space repair we see very often is replacing wet fiberglass in a 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 insulation 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.

The Risks of Using Fiberglass Insulation in Wet Conditions

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:

Sump Pump Complications
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 sump 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.

Trenching and Water Alarm Benefits:

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.

crawl space sump pump

3. Encapsulating 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.

Common Mistakes in Sizing and Draining Crawl Space Dehumidifiers

Many times the crawl space 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.

Monitoring and Maintenance: The Key to Effective Dehumidification in Crawl Spaces

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 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 epa.gov.

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.

Radon Risks in Encapsulated Crawl Spaces

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 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. This is another common bad crawls pace repair we see homeowners do.

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 mold and wood decay fungus damage.

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

A horrible crawl space repair is attaching vapor barrier to the sub-floor. We have ripped out many thousands of square feet of crawl space 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 crawl space 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 with a foundation fan 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 Bad Crawl Space Repair Tip:

Another bad crawl space repair we see is to upgrade your HVAC system but keeping the old leaky ducts and nasty inefficient 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

Contact Crawl Space Ninja for Basement Waterproofing and Encapsulation

Please contact us to schedule your assessment to fix your crawl space, basement issue. 


Do you need help with mold removal, crawl space encapsulation, crawl space insulation, vapor barrier, waterproofing, foundation repair, basement waterproofing, or controlling humidity in your crawl space?

If you live in Georgia, Delaware, North Carolina, South Carolina, Tennessee, or Kentucky, Crawl Space Ninja can help!


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42 thoughts on “10 Bad Crawl Space Repairs”

  1. 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.

  2. 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

    1. Your welcome Dean. I agree that a regular crawl space maintenance program is vital to ensuring the health of not only the crawl space but also the home. Many times we forget the crawl space or unfinished basement is part of our home so placing a remote humidity reader is a great first line of defense in keeping a check on humidity. High humidity can lead to mold and dust mites. Here’s a great product to remotely check humidity: https://crawlspaceninja.com/product/acurite-00611a3-wireless-indooroutdoor-thermometer-and-humidity-sensor/

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  4. 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!

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  6. 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!

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  8. 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.

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  10. 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.

  11. 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.

    1. Hello P. D. Miller. Are you located in our service area? https://crawlspaceninja.com/service-area/ If so, I would recommend we take a look at the crawl space. Another approach would be to contact some legitimate home inspectors and get their feed back. Crawl Space Encapsulation (https://crawlspaceninja.com/crawl-space-encapsulation/) is acceptable by building code when done properly so not sure their “opinion” should matter if they are against it.

  12. 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?

    1. 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.

  13. 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.

  14. Chrissy Buckley

    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 !!

  15. 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.

  16. 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?

    1. 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. https://www.youtube.com/watch?v=DghUv_qjPAs

  17. 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.

    1. 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.

  18. 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?

    1. 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!

  19. 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?

  20. 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?

  21. I live in Southern Maryland. I purchased a one-story home built on a cinder block foundation. The house was built in 1967. The house had two additions at a later date. One addition extended the Master Bedroom and the other addition extended the Living room. I discovered I have three separate crawl spaces. I had a mason removed a few cinder blocks to connect the Master Bedroom crawl space to the main home crawl space. Should I have a mason removed some cinderblocks to “connect” the living room extension crawl space to the main house crawl space (i.e. thus creating one single crawl space)? All crawl spaces have been encapsulated. I have a crawl space dehumidifier with fans for the main house and Master Bedroom crawl space. I have a smaller dehumidifier for the separate Living Room extension crawl space (est. 200 sq ft.)

    1. Hi Larry, are the dehumidifiers and fans allowing the additional crawl spaces to stay around 50-55% relative humidity? Is the wood dry? Normally you would like to see wood between 9% and 15%, lower is better. Are you considering removing part of the walls because the crawl space is not drying? We just released a video about crawl spaces that are sectioned off, please take a look. Hopefully it helps. Thanks for the question. https://www.youtube.com/watch?v=l028j1qX2gY

  22. We are considering encapsulation of our home crawl space. The home was built in 1934. I’m concerned that if we encapsulate, that it may impact the structure of the house negatively b/c it will reduce the moisture level in the structural wood. Any thoughts on this?

    1. Hello, the wood moisture content can certainly be a factor. If too moist can expand and cause damage and potentially grow mold and wood rot fungus. Too dry can extract and cause damage which is why we recommend a dehumidifier set at 50 to 55% to keep in optimal zone for humidity. I’d recommend getting a wood moisture meter and seeing what level you are at and decide from there. I hope that helps.

      1. I live in a 70 year old house, and recently widowed. I have become aware of crawl space issues, and have had two companies provide bids, but their remedies are confusing.

        There is insulation in the floor joists that must be removed before an encapsulation project. Neither company is discussing new insulation. I am expecting to find problems with flooring when insulation is removed. Does it make sense to do an encapsulation project without insulation? Could it be done after encapsulation? These are big, expensive issues for me, and I am trying to get it right the first time. Thank you for any guidance you can provide.

        1. Hi Alice, I am so sorry they are not doing a good job explaining the proper steps. We insulate all crawl spaces because residential building code and the Department of Energy says to do so. If you encapsulate you can do the walls (what we prefer) instead of between the joists. Yes insulation can be installed after encapsulation but normally doing it during the initial job can save you some money depending on who you hire. Here is a video that I hope helps guide you. https://youtu.be/9OjjZwii0qw

  23. Any recommendations what to look for in choosing a company to encapsulate a crawlspace? Location around Louisville ky. Thank you

    1. I am sorry John, we don’t have any recommendations right now. We are actively seeking a franchise owner in the Louisville KY area to help us open a location. We get a lot of requests in your area.

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