Is R-10 rigid foam for basement enough

Question

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.

Answer 1

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.

https://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers

Answer 2

"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.