GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Conditioned crawlspace — rim joist insulation

mpg9999 | Posted in General Questions on

Yes, another conditioned crawlspace question, I think this is number 3 for me. Our building permit is finally approved and construction is starting. I’ve talked to two different insulation contractors who do conditioned crawlspaces in my area (Coastal Virginia, zone 4). Both of them use closed cell spray foam on the foundation wall, and both leave a termite inspection gap at the top. One of them uses the spray foam on the rim joist, while the other uses fiberglass batts.

I know the spray foam is better at keeping the rim joist dry because it provides an air seal so you don’t have to worry about condensation/adsorption from warm air hitting the cold rim joist in the winter time. The problem with spray foam on the rim joist is that it can’t be removed for termite inspection. I talked to one local termite company today and they told me they won’t provide a warranty on a conditioned crawlspace where the foundation walls are insulated, regardless of a termite inspection gap or removable fiberglass batts on the rim joist. I’m going to call some other companies tomorrow and see what they say.

It seems most (or maybe even all) companies in this area use a dehumidifier in the crawlspace rather than providing conditioned air. My plan was to use conditioned air (along with a whole house dehumidifier from ultra-aire) as it’s probably more energy efficient than using a standalone dehumidifier.

So should I go with fiberglass batts on the rim joist and have a slightly higher risk of condensation (and will conditioning the crawlspace with supply air, which means it’s heated in the wintertime, increase the chance of condensation? Or should I go with spray foam and most likely void any kind of termite warranty I might otherwise be able to get?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    Termite concerns trump insulation issues, in my book. You should follow local advice on the best approach to minimize termite problems.

    Your winters aren't as cold as winters in Vermont or Minnesota, so the risk of rim joist rot due to the use of fiberglass insulation is much lower in your climate.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |