Should I Remove Insulation from Crawl Space

"Should I Remove Insulation from Crawl Space?" is a question we get a lot. This is because many contractors are telling homeowners it is not needed. Is that true? Is crawl space insulation needed, or is it better to remove it?

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.

Crawl Space Insulation is Key to Energy Efficiency

https://crawlspaceninja.com/blog/insulate-crawlspace/

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 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. We 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

https://www.buildingscience.com/documents/information-sheets/crawlspace-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.

Do you need help with crawl space insulation? If so, please contact Crawl Space Ninja or Basement Ninja and we will be glad to help. Also, let us know in the comments below if you'd like to suggest a future blog post.

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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.

6 Comments

  1. Keven on June 6, 2018 at 2:56 pm

    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?

    Thanks

    • Michael Church on June 16, 2018 at 10:20 am

      Great question – you can install foam board insulation over the vapor barrier but keep in mind if you puncture the vapor barrier, it may leach moisture through.

  2. Tim on June 16, 2018 at 7:26 am

    Where can you get the termite resistant crawl space insulation?

    • Michael Church on June 16, 2018 at 10:17 am

      Hello, we offer the foam board at $34.99 + tax for 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.

  3. Scott on March 13, 2021 at 9:10 am

    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)

    • Michael Church on March 22, 2021 at 12:14 pm

      Hello, if you are keeping the crawl space vented, foundation insulation will be ineffective. We only insulate foundation walls on closed crawl spaces. Hope that helps.

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