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

Uninsulated slabs-Still Business As Usual?

bHqUcamKme | Posted in Green Building Techniques on

I’m on my way to visit with a customer who’s planning to insulate his basement walls. As part of our utility’s rebate program, we require an on-site visit before and after the job is done to verify quality.

What’s frustrating in this case is that its a NEW HOME. Actually, the customer had a modular (Wisconsin Homes) home moved onto a new poured concrete basement/foundation. Not only did the foundation installer not put in any external insulation on the walls, but the customer says the slab wasn’t insulated either.

Is this still “business as usual” for contractors? If so, any ideas on how our utility can educate contractors on best practices?

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. user-723121 | | #1

    I believe MN code calls for R-10 foundation insulation, there was an R-5 option allowed if the furnace was direct vent with 90% plus efficiency. Most often the insulation is placed on the interior, I prefer rigid on the outside of the foundation for starters and then additional insulation on the warm side, between the foundation wall and the framing.

    As for sub-slab insulation, sadly this is not yet in the code. A minimum R-10 under the basement floor works miracles as far as comfort is concerned for lower levels in cold climates.

  2. GBA Editor
    Martin Holladay | | #2

    This is clearly a code issue. Since local codes are all over the map, it's up to you to research local requirements.

    Regardless of local codes, a slab on grade foundation in Wisconsin clearly needs to be insulated. Most energy experts recommend two types of slab insulation: vertical perimeter insulation as well as continuous horizontal insulation under the slab.

  3. user-716970 | | #3

    This is not a slab on grade as the OP refers to "basement walls"...

  4. GBA Editor
    Martin Holladay | | #4

    You're right, of course. I was obviously skimming, not reading.

    Curtis didn't reveal his location -- just that the name of the modular manufacturer is "Wisconsin Homes."

    Assuming he's up north somewhere, I can't imagine that building codes don't require basement wall insulation. Perhaps the home is located in a rural area without any building codes.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |