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

Crawlspace conversion damp-proofing and wiring question

KevinEJ | Posted in Green Building Techniques on
Converting small 12×16 vented crawlspace into sealed conditioned space and insulating walls and rim joist area with rigid foam. Zone 5b. This vented crawlspace has functioned fine for 2yrs with no insulation and no dampproofing or footing drain. The soil here is sandy and drains well, but the ground freezes every winter.
Since I am now closing it up and insulating:
1) Is it necessary to damp-proof and/or add a footing drain? Or will it continue to function fine without?
2) When insulating rim joist, can I foam in the romex wires that are in the area I need to insulate? Or is there a better way? (I have a couple wires that come into the crawl from the interior mounted subpanel above for lighting and a dedicated crawlspace circuit.)
Zone 5b

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. KevinEJ | | #1

    *Edited my question to be shorter in hopes of a response :)

  2. GBA Editor
    Brian Pontolilo | | #2

    Hey Kevin,

    Ideally, a crawl space foundation has footing drains and some level of waterproofing on the walls. I understand that you don't currently have a problem, but if you are doing all of this work now and retrofitting outside of the crawlspace walls is an option, it is worth considering, to prevent future problems.

    Cable gets encapsulated in spray foam all the time. So, there is no need to avoid that when insulating your rim joist.

  3. KevinEJ | | #3

    Thanks for the feedback. Always enjoy your perspective on the FHB podcasts. Excavation is beyond the current scope for this one-man team with shovel. In addition to the crawlspace, my plate is full with also finishing the space above.

    Will the "future problems" I'm trying to prevent be obvious? Could my half-steps create a harsher situation? Or will they be an improvement regardless?

    If a visible problem occurs due to skipping the drain/dampproofing, I could address those items next summer. I'm concerned of issues that could go unnoticed, such as rim joist rot or something catastrophic behind the rigid foam that will become impossible to visually monitor.

    A basic sensor will be kept in the crawlspace to monitor humidity and temperature. Polystyrene sill seal is installed between the smooth concrete foundation and PT mudsill, but there is no capillary break down between footing and stemwall. There won't be a termite inspection strip as they are a non-issue here, but cold is. There will be 4" of foam from the properly detailed 10mil vapor barrier up to the subfloor. I will double up on airsealing by caulking the interior sill seal joint and rim joist area before adding rigid with canned foam edges. Moisture content of the rim joist and mudsill currently average 6 - 7.5% and the concrete walls are visibly dry (and remained that way through two snow filled winters and the following weeks of snowmelt). This is with an imperfect 6mil vapor barrier that is not attached to the walls. I'm not subbing this out. I'm detail oriented, bordering on obsessive.

    Are my concerns unfounded?

  4. GBA Editor
    Brian Pontolilo | | #4

    Hi Kevin,

    If you know that the space stays dry because you have had plenty of time to observe it, then I don't think you are doing anything too risky by finishing your work in the crawlspace, just know that conditions could change at any time and that your exterior details are not ideal and may need to be remedied.

    I also wouldn't be too concerned with moisture accumulation at the rim unless it is getting wet from exterior leaks. If that were the case, it would be important to fix the leaks before insulating and air sealing the rim area.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |