I live in Ohio and embarking on finishing my basement. I am planning to put R-10 rigid foam boards between my poured concrete walls and the stud walls. I only have about 2 feet or less of the foundation wall above grade. Does anyone have experience with a similar basement that was only insulated to R-10? Would it be sufficient given that the exterior of the foundation is insulated and below grade?

There is so much conflicting information and conjecture that I haven’t been able to figure out if I really need to put batt insulation in the stud walls on top of the foam board or not.

For example. Currently only the above grade parts of the walls have foam board insulation. I work down there currently and while it is a bit chilly, a hoodie and socks and I’m comfortable. I’m wondering if the additional foam board with walled out rooms and a good flooring would be enough to make it comfortable without the added layer of a hoodie.


2 Answers 2


A couple of recommendations.

Look up the latest recommendations for insulating below-grade basement walls in your area.

Then, I think R-10 on your walls is more than enough, which wil reduce your heat loss through the walls by 90%. No need for batts on top of the foam board, though if you want to add batts you only need to do so for the upper 4 feet of the wall (2 feet above ground plus 2 feet below ground).

Also, when my previous house was built in 1989, they only insulated the top 4 feet or so of the basement walls, with some ~1 inch foil faced batts. This climate (Mid-Atlantic) is similar to yours.

Finally, you need to make a conscious decision what you're going to do about a vapor barrier/retarder.

Here's the best reference I've come across discussing vapor barriers.


  • I had read that 2inch thick Owens Corning Foamular when glued and taped will provide both thermal break and vapor barrier, as long as it is used four the entire wall. Commented Dec 10, 2022 at 15:08
  • 1) Do you need or want a vapor barrier (or retarder at all. And 2) if the answer is yes, do you want that on the inside of the wall (towards to basement) or on the outside of the wall against the block/concrete? See the reference I added in my answer.
    – SteveSh
    Commented Dec 10, 2022 at 18:37

"Enough" is a matter of opinion, depending on your climate and your budget and how much already exists and how much floor space you are willing to sacrifice and your skill level and what temperature you intend to keep that space at and...

Ignoring all those practical matters, anything is better than nothing and more is better than less. "In theory, practice should be the same as theory. But in practice..."

I'm in the northeast, I do not have insulation outside the foundation, and I chose to install something in the R10 range because it was convenient as a solo DIY project and consumed only 2" of floor space on each wall (not counting the blue board on top of it). That won't be the right answer for everyone.

  • Is it performing well? At the end of the day I don’t find the basement terribly uncomfortable now with nothing. So I’m thinking that r-10 with a decent thermal break on the floor will probably be enough to retain the heat. Commented Dec 10, 2022 at 17:13
  • Again, what do you mean by "performing well"? The basement is set at 61. It's holding at that temperature. I don't have any thermal break on the floor, the other half of the basement is uninsulated, the heat pump is relatively new... Many variables, many of which changed at once so I don't have direct measurements of this one change. My long-term rolling yearly average for the whole house is about 56MBTU counting both electric and gas, but ... apples and orangutans. Running the numbers on your place should give you more useful information than I can.
    – keshlam
    Commented Dec 10, 2022 at 18:37

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