Should I Remove Insulation from Crawl Space

Should I Remove Insulation from my Crawl Space?

This is a question we get a lot. This is because many contractors are telling homeowners that crawl space insulation

is not needed.

Is that true?

Is crawl space insulation needed, or is it better to remove it?

Bad Insulation Choices Should be Replaced with Insulation Designed for Crawl Spaces

I understand why some say it is not needed because certain types of insulation may cause more harm than good. Fiberglass insulation between the joists can house rodents. It can also enhance moisture problems that lead to mold and wood rot fungus.

I have even seen fiberglass insulation blown on crawl space walls. We have also removed cellulose insulation that was held up by netting between the joists. But what I feel is even worse is spray foam insulation applied to wet moldy wood. To me, since many contractors don’t understand how to properly insulate the crawl space, their default response is just to get rid of it.

Insulating Floor Over Dirt Crawl Space

Homebuilders have been insulating the joists of the crawl space for many years.

This old school way of insulation is still practiced today. In some cases this type of insulation is fine but humidity and water can wreak havoc. When fiberglass, rock wool, or spray foam attached to the sub-floor becomes wet, it often creates a mold or wood rot fungus problem.

Trapping moisture can happen during a plumbing leak or from a humid day.

Wet wood is not good.

Covering the sub-floor does not allow the wood to dry properly. Dirt floor crawl spaces or basements are notoriously damp. Installing a dehumidifier is recommended to control humidity. Sump pumps are used to address flooding and standing water. Neither will be effective at drying wood covered by insulation.

Knoxville Crawl Space Mold Prevention

Insulating Crawl Space Walls

So back to the question of “Should I Remove Insulation from Crawl Space?”

The answer is yes, if it is trapping moisture – but then replace it with proper crawl space insulation. The professionals at Crawl Space Ninja can insulate the sub-floor of the crawl space if the homeowner likes, but what we try to do is insulate the walls of the crawl space.

Building Science Crawl Space Insulation

Water Resistant Wall Insulation

When water-resistant wall insulation is installed properly, it creates a thermal barrier. The foundation thermal barrier is more effective versus the sub-floor thermal barrier in a closed or encapsulated crawl space. If your crawl space is open or vented, sub-floor thermal barriers are recommended.

Wall insulations include foam board and insulation vapor barrier. Both are very effective at controlling crawl space temperatures. Many homeowners don’t worry about pipes freezing with a properly insulated and encapsulated crawl space.

Contact Crawl Space Ninja for Foundation Waterproofing and Encapsulation

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


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31 thoughts on “Should I Remove Insulation from Crawl Space”

  1. Hi Michael,

    My new encapsulated crawlspace has nine mil vapor barrier on the ground plus “curtained” pieces hanging down the walls and taped to the ground piece.

    How can I insulate with foam board? Is it ok to attach the foam board on top of the vapor barrier on the wall or do I have to cut the seam, lift the wall vapor barrier pieces and insert foam board behind?


      1. natalie wohlers

        Hi Michael ,

        my crawlspace has no barrier yet but the insulation under my floor boards is in upside down and has mold . is it ok to remove insulation without my barrier .
        my thoughts are to remove insulation
        get mold out
        do barrier
        then insulation under floor boards

        please advise if it’s ok to have no insulation with no barrier

        1. I like your process but make sure you dry wood before addressing mold and installing insulation or mold may return. Humidity needs to be controlled year round. Hope that helps.

    1. Hello, we offer the foam board in R-10 4×8 sheets but we don’t offer shipping so it must be picked up. Hope that helps. You can call our office (865) 659-0390 if you’d like to place an order.

  2. Hi Michael,
    I’m concerned that installing foam board insulation against the block walls in the crawl space will trap moisture to the block wall and cause problems. Is this an issue? (The block walls are do have some moisture after 20 years) If, keeping a crawl space vented, is the best option to just insulation the floor joists with rigid foam? (I prefer to not close vents as it traps more radon gas)

  3. What do you recommend for the following scenario?

    48-60” crawlspace height, 24” of it is above grade, the rest is below grade.

    14 mil floor, 8mil curtain. The wall curtain goes up to the last cinder block, leaving 8” of the cinder block exposed. I have fiberglass in floor joist, but they feel dry. Joists don’t look like they are damp either.

    Humidity is 70-80% in crawlspace still after vapor barrier was put in.

    Should I just seal the 3 vent windows and put a dehumidifier in and go from there? or what do you recommend?

      1. Hello I have a crawl spacethat has damp insulation in floor joist.thaplastic is also hanging down in places. I just closed off my vents to the crawl space and installed 2 inch styrafoam s m and about to cover dirt floor with vapor barrier question. Can I remove the insulation in floor joist and leav it open

        1. residential code wants you to have insulation in the crawl space. if you keep the crawl space vented then a sub-floor insulation meeting your areas R-value is recommended. Hope that helps. thanks.

  4. Hi, I have recently noticed my crawlspace isulation under the subfloor is damp. The crawlspace was originally vented with subfloor insulation. I had the walls sprayfoamed and vents sealed off. Can I remove the insulation from the subfloor?

    1. Dept of Energy says a sealed crawl space only needs foundation insulation so yes if you have sealed your crawl space, sub-floor insulation would be unnecessary but if your crawl space is damp, please consider a dehumidifier.

  5. I have a brick foundation built in 1939 varying from 18″ to 24″ in height; the brick mortar was not finished, leaving a very irregular surface. Would you recommend foam board insulation for this surface? I am in the process of removing fiber glass sub-flooring insulation, then will do mold remediation prior to encapsulation. Thanks for your reply.

      1. Thanks for your reply, Michael,

        The foundation in my crawl space is 18″ high. Allowing for a 3″ termite gap, I have 15″ of foundation to play with. If I use the insul-barrier, do I allow the 33″ of excess to cover the floor? I would run the other barrier up around 8″ and tape to the insul-barrier. Does this read copacetic to you?

  6. Charlie Schober

    Follow up to my last inquiry: I believe that I will need to employ the spray foam and foam board. The insul-barrier seems to be impractical.

  7. I have a crawl space with3/4 stone floor and a vapor barrier over top of it. In the joists is fiberglass batt insulation. I want to seal off my vents and put rigid foam board on the block foundation walls and in the rim joists. Would you recommend to remove the fiberglass batts? Would I need to add a dehumidifier in the crawl space since I would be sealed up essentially? Thanks!

    1. You probably need a crawl space dehumidifier if you live in humid part of country. The sub-floor insulation should be removed if it has been wet or moldy. In our experience sealing the crawl space without a dehumidifier is not effective. Hope that helps.

  8. I’m helping my son encapsulate the crawl space on the 30 + year home he recently purchased. We have already sealed all oversized non-vent openings for plumbing, HVAC, and drainage, and have completely sealed the 9 vents. Although there were 2 layers of polyethylene on the floor, they did not have taped seams so we put down new 6 mil polyethylene on top of the old layers and sealed all seams. We next plan to glue 2 inch foil faced rigid foam board to all vertical wall surfaces and tape any seams. I’ve also told my son that we will need to purchase and install a dehumidifier. Once encapsulated, my question is: Do we need to remove the old fiberglass insulation from the joists, or can it stay in place even though we understand that it isn’t necessary? We have not been able to find clear guidance on this anywhere.

    1. Hi Jim, If the sub-floor insulation is in good shape, no moisture in sub-floor or mold I would leave it in place. Keep in mind it could still hide future leaks or be a critter nest area. Hope that helps.

  9. I’d like to remove my batt insulation but I can spray foam the rim joist for some time. The space will have a dehumidifier and the vents sealed. Is it okay to remove the floor insulation and wait a month or two until I can get the spray foam in?

  10. Hi Michael,
    I have a summer home in Delaware. My crawlspace was encapsulated almost 10 years ago and I use a SaniDry dehumidifier. The ceiling insulation is 40 years old. Is there any reason to keep it? Or should I have it removed? It doesn’t look very good. Also, since I am only here 3 months during the year, should I turn the dehumidifier off when I depart? Are there wi-fi options to monitor the dehumidified from my permanent residence? Thanks.

    1. Hi Bill, I am not a fan of subfloor insulation due to it’s ability to trap moisture and house pests but I don’t think it should be removed if it is in good shape and the wood joists and subfloor are dry and mold free. When we encapsulate we install wall insulation so the crawl space is still insulated and remove subfloor insulation. DOE still wants the crawl space to be insulated even if encapsulated. I am not familiar with a remote wifi that works with the Sanidry dehumidifier but I would keep the dehumidifier set to run at around 50% all year. It will run more in summer and less in winter most likely but the alternative to not running it could be mold and wood rot fungus. Hope that helps. Thank you.

  11. The crawl space in my 20 year old house needs work. It’s vented and there was only plastic sheeting on the dirt floor without taping any seams when it was built. Some of the fiberglass insulation is sagging and looks like it needs to be replaced. And there is sign of mold due to moisture buildup. We were recommended by an HVAC person to keep the crawl space vents closed to reduce humidity under the house but I’m guessing this is what caused the mold as there was no air. I’d like to remove and replace damaged pieces of the R19 insulation currently installed and install an unfaced insulation over that. Is that recommended? Also, should I close off the vents and install a foam board to seal them off? If I do that, should I also install reflective foam board with built in vapor barrier on the walls? Lastly, I’d like to install a vapor barrier on the floor. Can I do that with the reflective foam board on the walls?

  12. I live in very cold winter climate. My dirt floor crawl space emits cold during winter months. There are no obvious moisture issues. Maybe elevated air humidity during summer. Radon is also present in the soil ever so slightly above 4.0 pCi/L. The exterior block walls are insulated with foam board insulation and drywall over that. I covered the dirt floor with 6 mil plastic and installed a 3/4” strand board plywood floor sitting on a wood frame on top of the plastic. I still feel a cold draft from the space. Should I insulate my crawl space dirt floor between plastic and plywood? Best material? Should I encapsulate over the wood floor? Should I vent for the radon? All of the above?


    1. Hi Dan, have you used a spray foam sealant and air sealed rim joists and subfloor penetrations? Also, have you insulated the subfloor with batts or other type of insulation? I would not put plastic on wood because it could trap moisture.

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