I'm looking to finish part of my basement to create a bedroom for my growing family. Our home was built just last year, and since we live in Wisconsin, we're dealing with freeze and thaw cycles. The foundation has waterproofing, and we installed 2 inches of rigid foam insulation around the perimeter before backfilling.
I've spent a lot of time reading about basement finishing, but I'm still unclear about the next steps. We plan to use insulation wall batts on the interior, but should we add rigid insulation against the foundation walls before putting up the studs? Since we already have exterior insulation, is that necessary? I get the feeling that the foundation is now part of the thermal envelope.
I've also heard about the idea of leaving a half-inch air gap between the concrete and insulation for movement. That seems old-fashioned to me. I'm just hoping for some guidance on the right approach.
1 Answer
You might not need additional insulation on the inside since you already have that rigid foam outside. The point of insulating the exterior is to reduce the need for interior insulation. Just remember, if you choose to insulate the inside, avoid using a vapor barrier since the exterior foam should handle that. And be careful with spacing the insulation off the wall, as it can mess with the insulation's efficiency.
Also, just a tip: ensure your exterior foam is continuous and connects well with your ground-level insulation. If it’s not done right, it can defeat the entire purpose of your below-grade insulation!
Got it, we'll consider skipping the wall batts then. Thanks for the insight and for sharing the article link—it looks useful!