Crawl Space Repair Mistakes

The Lack of Standards in Crawl Space Repairs

Crawl space repair mistakes are common because there is no real standards for crawl spaces. Crawl space mistakes could wind up costing you thousands of dollars or the sale of your home. Crawl space encapsulation is a great way to make your crawl space and the rest of your home dry, clean, and efficient.

Navigating Conflicting Advice on Crawl Space Repair and Waterproofing

The problem is there is no standardized methods for crawl space repair or crawl space waterproofing. It is sorta like the wild west when it comes to crawl space repair. Pest control companies tell you to add more ventilation. Crawl space guys say, “dehumidify. Remove the insulation before you address mold. Don’t remove the insulation. You don’t need insulation.”

Here is a list of some of the biggest crawl space repair mistakes we come across. Trust me there are a lot more but guarding against these five is a great start. If the company you are hiring recommends doing these, make sure you get another opinion.

Crawl Space Repair Mistakes #1

We don’t need to remove the batting insulation between the joists to address mold.

My question is how do you as a homeowner know the mold was addressed if the insulation was not removed. Mold can’t grow behind the insulation, right? Sure it can. Many times the insulation is trapping moisture behind the vapor barrier (paper attached to batt insulation). The paper on insulation can’t grow mold. Ehh (my buzzer sound), wrong again. We have seen thousands of square feet of kraft paper growing mold while attached to the insulation.

Whether you have rock wool, fiberglass or blue jeans all those materials can hold water plus dead crickets, mice feces, etc. Those items can grow mold inside the insulation even if the insulation material supposedly won’t. Make sure you remove the insulation to avoid this crawl space repair mistake.

Crawl Space Repair Mistakes #2

Just spray the mold, don’t remove it.

This is another issue we see a lot in our industry where a company convinces the homeowner to just spray the mold with a disinfectant without physically removing the mold. Those same crawl space repair people are also telling them to leave the insulation in place while spraying. So if you leave the insulation and spray a disinfectant you are saturating the insulation with a liquid and only treating 10-20% of the crawl space floor joists. No sub-floor, rim joists or sill plate is being treated. The weight of the disinfectant being trapped in the fiberglass can also start to pull the insulation from the sub-floor.

Consequences of Inadequate Mold Treatment During Home Sale and Inspection

Another problem is when you eventually try to sell your home and the home inspection shows a floor joist covered in mold. I am sure he will flag it in his report whether it is dead or not. Even dead mold is an allergen. We recommend removing and disinfecting the mold. Hand scrubbing or soda blasting are great ways to accomplish mold removal in your crawl space. Make sure you remove the mold to avoid this crawl space repair mistake.

Crawl Space Repair Mistakes #3

You don’t need to insulate an encapsulated crawl space.

This is an easy one because code requires all crawl spaces to be insulated. I guess the argument could be made that you don’t HAVE to insulate your attic either. Crawl space insulation can be applied between the joists or on the walls of the crawl space. If the crawl space is vented then joist insulation is recommended. If the crawl space is encapsulated either can be used but we recommend insulating the block walls. Make sure you install insulation to avoid this crawl space repair mistake.

Rim Joist Insulation

We and the engineers at also recommend air sealing the rim joists. Air loss from the crawl space into your living space is a huge waste of energy. The rim joists is one area where a lot of air exits your crawl space.

An alternate detail that addresses these condensation and air barrier details quickly and easily is known as the “critical seal”: spray urethane foam insulation is applied to the relevant surfaces, connecting them as an air barrier.  In practice, our measurements have shown that this detail provides outstanding building air tightness (when combined with cavity-fill insulation above-grade walls with good air tightness detailing). ~

Crawl Space Repair Mistakes #4

The dehumidifier kills the mold.

What? Who says that? Mold cannot be killed by removing water, moisture or humidity. We just went on a call where our competitor said all you need is a dehumidifier and the mold will die. If you think that is true please call Assured Bio Labs in Oak Ridge, TN and speak with one of the smarties (microbiologists) there and ask them that question. Mold can only be addressed with a disinfectant or soda blasting. Please understand that a dehumidifier is vital in preventing the mold from returning.

Also, if the sub-floor and joists are too wet they need to be dried before addressing the mold but a dehumidifier is not a mold remediator. Make sure you perform mold removal with soda blasting to avoid this crawl space repair mistake.

Crawl Space Repair Mistakes #5

Condition the crawl space with the HVAC system.

I would say 99% of the time this is untrue in East Tennessee. Here are two problems with using the HVAC system alone to control humidity.

1. If you have an existing HVAC system that was not sized to include the crawl space and then you add the square footage to the load of the unit, you just undersized your system.

2. If you do have a properly sized HVAC unit which does take in the consideration of the crawl space that is great. The other problem is the homeowner and the comfort level you like the home at during the seasonal changes. For example, you may keep your windows open in the spring and fall. That’s great if you do but you just bypassed your homes dehumidifier (the air conditioning system) and now your crawl space is getting no love. It’s humid in spring and fall even though the temperatures are cooler.

If you want to condition the crawl space with your HVAC system and get down there and change filters, no problem. I would still install a dehumidifier as a backup or at least put a remote humidity reader in the crawl space to make sure you know the humidity levels year round.

If 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 like.

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67 thoughts on “Crawl Space Repair Mistakes”

    1. Carolyn pursell

      I was told I need to insulate with Matt insulation between the joust and only escapulation the floor and wall of the crawl space
      do i need to batt insulation and escapulation the ground and walls also?

  1. It was intriguing to learn that many times the insulation is trapping moisture behind the vapor barrier. I remember one day waking up and smelling something awful! We found out that it was the mold in our crawl space and that a pipe had broke! Next time we get insulation I will be sure to ask if this may happen again to be aware of any signs!

      1. My crawl space is dry and well ventilated. Can I just remove the batt insulation and have the joists and subflooring exposed?

    1. Carolyn pursell

      I was told I need to insulate with Matt insulation between the joust and only escapulation the floor and wall of the crawl space
      do i need to batt insulation and escapulation the ground and walls also?

  2. Your 5 most mistakes about encapsulation correctly was very helpful. We are having our crawlspace done next week. Our home is 10 years old and we have water pouring through the blocks. We have been using a sump pump and we now have some mold. We do have a question. Is the dehumidifier 1850 series a efficient model. Do you believe we will see a large jump in our electric bills from running the dehumidifier and also removing the insulation under the floor causing higher heating bills.

    1. Hello Donna, Thank you for the feedback. The Aprilaire 1850 is Energy Star rated and has been a great product for our customers. All homes are different but we have not had any complaints about the Aprilaire 1850 dehumidifier causing a big increase in energy bills. Please take a look at the owners manual for more information.
      And here is the link to order if you decide to get the 1850:
      Great question.

  3. not sure if this post is still active, but I have a question. I have a company that is going to dig trenches and place a sump pump system in my crawl space. they are going to remove the old insulation and disinfect the beams, lay down new poly etc. they told me they will put new insulation in the floor, but wont put it on the block walls because they are finding it traps moister in the block wall, and can cause damage over time. Do you know if this is correct?

    1. I have heard this over and over and not once has anyone shared any real evidence this is true. My thought is, if sealing the wall where water intrudes causes the demise of the wall then the interior basement waterproofing industry will be rebuilding a lot of homes because that is how they address water issues inside the homes with basements. I hope that helps. Thanks for the question and if you find any science/data or if the contractor gives you any please feel free to post it for us.

  4. I do not have standing water, but there is a slight amount of water covering (like a light dew) the plastic ground cover (its not sealed). The insulation is also damp. I plan to have all the insulation and ground cover removed and encapsulated with a dehumidifier. Is a sump pump necessary?

  5. Hi,
    I have a 70 pint dehumidifier in my crawl with a garden hose running through a drilled hole in the crawlspace door and out to a floor drain. The humidity is in the 60s and I get a lot of bugs. The crawlspace is encapsulated with 20 mil plastic. Would I be better off installing an actual “crawlspace dehumidifier” like the Santa Fe unit and how would it be any better if it is rated to remove say 55 pints only? The Santa Fe, and other crawlspace dehumidifiers, are much more expensive than the portable ones so I want to be sure I’m making a wise purchase before forking out so much money. Also, do any of those units have an attachment for a garden hose? Thanks!

    1. Hello, great question. Hopefully this video will help Also most dehumidifiers will need an coupling to go from the dehumidifier to a garden hose. You may want to wait until you purchase it to see which attachment you will need. The Aprilaire brand is what we recommend. Here is a link to those and the manuals on the pages may help you decide. We hope that helps, good luck. FYI, our dehumidifiers come with free shipping.

  6. Good Morning.
    I have a concrete wall and floor crawl space about 625 sq ft. No water comes in and the space has 2 vents. No wall insulation and floor is not sealed. I put a humidity gauge and it registered 52% after a rain fall. I would imagine it would be twice that in the summer months, I live in Chicago. I use the space for some storage. I’m worried that if I encapsulate, it will trap the moisture underneath the VB. My plan was to coat the floors and walls with Drylok, then install foam insulation in the wall, seal the rim joist, seal the vents and purchase the 1830 Dehus. I may actually install fan in one of the vents just as an option to vent. In case I run into radon issues. The house is been like this for 30 plus years, some mold but not as bad due to no standing water. Is this a sound plan? I believe the limited mold growth is probable due to the house not the being tightly sealed. The house was built in the late 60’s so its not as sealed as today’s homes.
    I really appreciate all that you do informing us with your videos. Thank you.

    1. Hi Ed, I honestly would never use drylock and here is a video explaining why: If you don’t have standing water, I think if you start with dehumidifier and vent fan, that would solve the humidity issue and dry rim joists. Then you can add foam board to walls and insulate rim joists. Not sure vapor barrier is needed either since you are all concrete and block.

  7. I have an open crawlspace that I plan to encapsulate. I will add a dehumidifier and poly floor and walls. Do you recommended spraying with fungicide prior to enclosing? Do you recommended removing all insulation on floor joists and pipes before encapsulation? Do you recommended re-insulating any part of crawlspace such as the walls. I live in South Carolina. We have problems with the hardwood floors warping in living areas on first floor of house.

    1. Hi Karen,

      Hardwood floor warping is a sign of high humidity in the crawl space. We’d recommend you address mold after drying out the crawl space, but before encapsulating. Fiberglass insulation may need to be removed to fully disinfect any mold. Building code requires that you have insulation in your crawl space, so you can reinsulate the joists or insulate the walls but you don’t have to do both.

      Hope you find this helpful!

  8. Hi Michael, Your posts and videos have been SO helpful as I sort out crawl space issues after buying our first home last year (not far from you, near Franklin). The house has a 1200 sq ft crawlspace with a good condition (approx year old) 12 mil plastic vapor barrier on the ground that is not sealed to walls. When I go walk around down there I’ve never felt/heard soft ground as evidence of water. About six months ago we added a SantaFe Advance 2 dehumidifier and closed the vents after seeing the relative humidity was around 70% in the summer and smelling some odor, seeing a small amount of mold on subfloor joists. Humidity is now under control, but we see radon spikes when it rains (and higher than we’d like even without rain, though <4) and we have 2 little kids in the home. We've gotten a few quotes for radon mitigation with or without encapsulation. The home is on a slight grade, so the rear of the crawl space is 5.5 ft tall, but it's only about 3 feet tall at the front of the home. To make a radon mitigation pipe/fan system effective, it sounds like we have to seal the membrane to the walls and around the piers down the middle of the crawlspace, but if we do that, should we just pull it all the way up the walls (i.e. full encapsulation)? In the TN summer our dehu could maintain humidity below 60 but it ran a lot (I can gently hear it cycle on and off while standing above it in the home). Lastly, 3 of the 4 exterior foundation walls are concrete block, the fourth is wood (brick on the outside, plywood inside with studs every foot and a half or so, so it's not a flat surface). How would you recommend sealing the barrier to wood? Two bids said spray foam that wall… another said don't encapsulate the walls for fear of trapping moisture between them… Any advice is gratefully received!

    1. Hello, thanks for the comment. we don’t recommend sealing the plastic to wood. It will trap moisture and if you spray foam it will trap moisture. With radon you must use polyurethane caulk to adhere vapor barrier to itself (overlap) and to walls. EPA regulates Radon so they have their own rules for that. I know you are wanting to address radon and mitigation is a great way to do it but you have a unique situation with your wood wall. Have you considered a high power ventilation fan to draw air out before it goes beyond the sub-floor? This could be a DIY project Hope that helps. EPA says 1cfm air every 50 sq feet so this fan may do the trick. open 1 vent and run 24/7.

  9. I have an encapsulated crawspace in south Florida and it is being recommend by the company to revome the insulation between the joist. I am being told this can continue to trap moisture and lead to damaging the joists. It will be costly so I am want to know if this is correct before I spend the expense to remove it

    1. Hi Gus, this is true. It can also hide leaks from your living space, if you happen to get one, and even mold. If you are already controlling moisture in your crawl space, the insulation is not retaining any moisture currently, and you have checked to make sure there is no mold hiding behind the insulation backing, you should be okay to leave it. But we do generally recommend removing the floor insulation and insulating the crawl space walls with foam board instead. You have to have one or the other according to building code but you don’t need both. Hope this helps and thanks for leaving a comment!

  10. Hi Michael.

    I had an area of my crawl space that was not covered in plastic and flooded during Hurricane Florence. I used a sump pump to rid the crawl space of standing water and aired it out for a few days. It seemed to be fine, so i then put down 6 mil plastic and ran it up the concrete wall and adhered it to the wall. It is extremely humid during our summer months and all seemed to be fine until i looked under yesterday and saw mold underneath the plastic at the seems where the plastic meets the wall and underneath at the opening near the door. What do you recommend i do to remedy the mold underneath? All of the mold is adhered to the plastic.

  11. I plan on encapsulating a crawl space under a modular home in Montana (Zone 6). Rim joists and foundation walls will be spray foamed. Does the existing floor foundation need to be removed?

  12. I have a dirt floor crawl space with cinderblock walls. I want to insulate the walls and put in a vapor barrier. Should i install the vapor barrier on the walls before or after I install the rigid foam insulation on my walls? Should the vapor barrier go all the way up the wall?

    Thank you

  13. Joseph Pignataro

    Great info on your website, Im curious as to the no-batt insulation between the joists- what about a radiant floor system over a properly encapsulated crawl space where the foundation walls are insulated? Almost every radiant floor manufacturer requires the joist cavity to be insulated for heating a space or as a supplemental to take the chill off. Or do you think a radiant floor (tile finish) would even be needed in a climate like eastern TN with an encapsulated crawlspace? Thanks!

    1. That is a great question. I know I would like radiant floor heat in my home. You bring up a great point. As much as I dislike batt insulation between joists, I feel that is a good time to use it.

  14. When isulating floor joists I’m crawl space is it wise to use a fully encapsulated fiberglass insulation instead of the open face kraft paper insulation ?
    If installing using kraft face, does the Kraft face up towards living space or down towards crawlspace floor ?

    1. We don’t use insulation encased in plastic but some areas of the country actually require it. My thoughts are moisture can still enter the plastic if not taped or rips during installation so I don’t see a huge benefit for protecting the insulation. If you install Batt Faced insulation, the paper should go against the sub-floor according to the manufacturer. Paper faces living space when possible. Hope that helps.

  15. We bought a house with a sealed crawl space. The floors in our house are very cold in the winter. Can we but insulation under the floors to help with this problem? We called an insulation company that said that sealed crawl spaces are not insulated. Why? Thanks for answering this question.

    1. Hi Sharon, sealed crawl spaces should be insulated and code even says they should. Unfortunately there are a lot of contractors that don’t insulate crawl spaces and many homeowners that are price focused that go along with it. We always propose insulation in our crawl space packages. If your crawl space is not insulated, yes insulate it but remember in order for floors to be considered “warm” they must be at a temperature higher than your body temperature. proper insulation only hold the heat that is already there. It will not add heat. Hope that helps. Here are 2 videos that may help too. “Crawl Space Air Seal Insulation | 3 Vital Crawl Space Air Seals | DIY Air Sealing the Crawl Space” and “Will Spray Foam Insulation Make Floors Warm? | Crawl Space Insulation | Crawl Space Floor Insulation”

  16. Love all your videos! My worker just installed faced fiberglass between floor joists in a vented crawlspace, putting the paper side down facing the ground. Will it pass code or do I need to have him flip it over so paper is against the wood?

    1. Thank you Sheila. In Tennessee it would not pass code for the paper to be face down in certain local municipalities. Before you have them change it out, you may want to call codes department just to be sure. Thanks for watching, hope that helps.

  17. Pest control has informed me that foam board insulation can harbor termites (and potentially attract them, though the verdict is still out on that), and they recommended we not install foam board insulation on the walls of the crawl when encapsulating. They may not warranty the house against termites if I install it.
    1. Is that true about foam boards?
    2. Is Rockwool an option that would not attract termites or harbor them?
    3. What is the disadvantage to using batt insulation above between floor joists vs. foam boards on the foundation wall in a fully encapsulated crawl space?

    Thank you

    1. Our foamboard is termite resistant. My understanding is most insulation could harbor them unless treated with a termite preventative. Cellulose comes with or without preventative. Here is our board if you’d like more information along with a video that could help. Thanks for the question and hope that helps. Video: Do You Need Subfloor Insulation? | Fiberglass Insulation vs. Foam Board

  18. Stefan Cristea

    Not sure this is active but here’s my issue.
    I’m about ready to start a dyi crawlspace encapsulation project at my house in Portland, OR. We had racoons nesting in there and made a mess. It’s all remediated and cleaned now, mold was removed and treated and, to avoid future head aches, we decided to encapsulate.

    After checking the tips provided by Ninja my plan is to:
    1. Seam the new vapor barrier that was installed by the crawlspace remediation company we hired to clean the space (it’s the type that is usually used for encapsulation projects)
    2. Close the air vents and all other places where there is gap to the exterior with foam
    3. Insulate the walls of the crawlspace with foam boards
    4. Install and dehumidifier and fan for radon gases.

    My questions are:
    Do I also have to install subfloor insulation if I encapsulate?
    What foam do you recommend for closing the vents?
    What foam board do you recommend for crawlspace wall insulation?
    Is there anything that I’m missing in my description above? Also, is this the right approach?

    Thank you so much!

    1. That sounds like a great approach. If you want to make the home even more energy efficient, you could air seal rim joists and major sub-floor openings around plumbing, HVAC lines. You can use a foam board similar to ours to insulate walls and seal vents. If you can’t access our EPS board with termite resistance you can use any board to seal vents. I’d recommend at least 2 inch thick. Here is an alternative to foam board for foundation wall insulations we use, Insulation Barrier Lastly, you can insulate the sub-floor but in our experience it does not offer you much of a return on your investment with the wall insulation. Plus it can cause other issues if your home floods from the living space down or has a slow water leak. Hope that helps.

  19. Hi Michael,
    Thanks for your youtube videos. They are great and so helpful. We have a vapor barrier but had a chimney leak on our new house that caused lots of mold in the crawlspace. Unfortunately, we also had a dehumidifer but it stopped working and we didn’t realize it. We’ve now installed a new dehumidifier. My question is…. should you a) clean the mold before removing the old vapor barrier or b) remove the old vapor barrier, then clean the mold.

      1. Hi Michael. I have a small crawl space under the laundry room about 50 square feet, which is connected to the unfinished basement. The crawl space was vented to the outside and separated from the basement with 3′ x 4′ door.

        Recently we had the crawlspace enclosed. The outside vent was sealed off, the walls insulated, drain board on the floor with insulation, and then the floors and walls were encapsulated. The door between the crawl space and basement was removed – so essentially it is one space. A dehumidifier and sump pump take care of humidity for both basement/crawl space area.

        My question is about finishing my basement… While the crawl space insulation seems good for an unfinished space – what happens when the entire basement is finished? The crawl space is still cool place and would like to keep the basement warm in the winter. How do I add more insulation to the crawl space area to keep more cold out? Can insulation be added on top of the encapsulation? Thank you.

        1. I think it will be difficult to keep crawl space warm if there is no heat source in the crawl space. The basement has slab to help against cold dirt some while crawl spaces has none. If basement has a heat source, it will always be warmer and lose that warm air to the crawl space. It may be better to have a dehumidifier in basement and a crawl space dehumidifier and treat the humidity in each separately then reinstall the door. Hope that helps.

  20. We were told that just encapsulation was enough to kill mold in our crawlspace. Is it possible to go
    back and remediate the mold after encapsulation? Is it necessary?

    1. Hi Becky, it is possible but depending on the methods used to remediate the mold, it could damage plastic and the dehumidifier. Is it necessary is a question only you can answer. Some feel it is extremely necessary and others do not. I personally want my family breathing the best indoor air quality possible and mold can certainly impact that. Hope that helps.

  21. Thomas Clarence

    It was really informative when you mentioned that encapsulation is an effective way to keep your crawl space clean and dry. I would imagine that molds could grow in your crawl space pretty quickly if there is any kind of moisture. As far as I know, this mold can spread to other areas of your home if you don’t remove it promptly.

  22. We had 14mil encapsulation liner installed today 6-8” up the walls in my crawlspace. A 70 pint Aprilaire 1820 installed, drain spout extensions, vents sealed off, mold cleaned from the wood and all old insulation removed. He said he doesn’t normally put insulation back because it’s not needed in a controlled space. Is this true?

    1. Hi Jessica, the Department of Energy says crawl space insulation is needed when building the home whether the crawl space is encapsulated or not. Not sure why people in our profession tell you it is not needed after moisture control is installed. Our local code enforcement requires insulation. If insulation is not needed in a controlled space why does your living space exterior walls have insulation? The living space is controlled. Saying all that, even if not “needed” your home would be more energy efficient with a properly insulated and air sealed crawl space but it is required. Hope this article helps:

  23. Curious about soda blasting to remove mold or fungus on floor joists. I live in North Carolina and wonder if that is something that people do near me. Also, I have violated the non removal of insulation before installing a ground cover and a dehumidifier. I checked the moisture level in my floor joists and it averages about 6.5%. Is that too dry or OK? My dehumidifier is the Aprilaire and have it set on 50% RH.

      1. Hi Michael
        I have a fairly small home of about 1300 ft.² included in the 1300 ft.² is an addition. So I have two crawl spaces separated by cement blocks they are dirt floor. I currently have fiberglass Matt insulation in the subfloor and vapor barrier on the floors. I get water into the front crawlspace and have something here. There still is moisture however in both crawlspaces and I’m starting to see white dotted What I suppose is mold on some of the wood in the back crawlspace. Between the front and the back crawlspace in the cinderblocks is a small opening big enough for wires to pass through. My question is do I need to get to dehumidifiers two vent fans for each crawlspace ? Or do you think I can get a larger opening into the cinderblock wall separating each crawlspace and only have one dehumidifier and one vent fan? I think you so much for any advice.

  24. Absolutely! Crawl space encapsulation is an excellent technique to keep your crawl space and house dry, neat, and effective. The issue is that there are no established procedures for crawl space restoration or waterproofing.

  25. My crawlspace was wet before I bought my home, so a vapor barrier was laid, vents were enclosed, and a dehu was installed. 3 months ago all looked fine. Today, multiple joists are cracked almost all the way through because they are too dry! What do I do?? Help 🙏🏼

    1. Hi Kara, do you know what the humidity and wood moisture levels are in your crawl space? If not, I recommend finding out. You can call an inspector or purchase meters to measure. Also, you can adjust the dehumidifier to not run so dry but if it does not have a digital display to show what setting it is, you will need a meter to help guide you. Best humidity setting is 45% to 55%. Hope that helps. Here are links to meters to measure moisture:

  26. Hi,

    I’m attempting to DIY my encapsulation, but I can’t find an answer to this question anywhere (sorry if I missed it!). I live in a split-level so one of the walls of my crawlspace shares a wall with an interior conditioned space. Do I need to foamboard insulate the shared wall (and rim joist area)?


    1. It may be advantageous to insulate rim joist to keep drafts from entering living space. If the temperature on one side of the wall is significantly different than the other side, I’d insulate the wall too. Hope that helps.

  27. We both a new house with an unfinished crawlspace with mold and shearing damaged. It is 2 feet in height and many companies are refusing to work in such a tight space. What’s the best way to increase the height so that we can even entertain someone doing mold remediation and encapsulation?

    1. Great question, digging out can cause some issues without a structural engineer guiding you on that. We have removed ductwork and subfloor in some instances to gain better access, is that an option? We have see homeowners dig tunnels out too but that could lower the access to the water table and cause flooding.

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