GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter 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

Sub slab insulation

Kurt S | Posted in General Questions on

Looking for some thoughts on sub slab insulation on a new build.  I am in zone 5 central Indiana.  Right now we are planning to build slab on grade with insulation on the inside of the stem wall.  The house will be double stud wall roughly r40 with r6o ceiling.  The house will also have all exposed concrete floors.  I realize that no matter what i do the floors are going to feel cool but I am wondering how much insulation under the slab would help with my house heating load as well as the way the slab feels.  Planning to heat and cool the house with a pair of mini split heat pumps.   Thanks for any feedback.

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. Expert Member
    Michael Maines | | #1

    Kurt, R-8 (2" of EPS or aged XPS, preferably recycled due to carbon emissions) will reduce your energy loads and keep the surface of the concrete near room temperature. More insulation will further reduce your energy load and improve comfort. Going beyond R-10 (2 1/2" of EPS or XPS) will probably not make financial sense, but you won't have another chance to add insulation at that location.

  2. Doug McEvers | | #2

    Michael has it right, R-10 or there about will add substantial comfort to the concrete floor. The floor will be close to room temperature as opposed to average 60F for my uninsulated basement slab in Minneapolis right now on January 3. This is in a full basement.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |