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

retrofit stem wall insulation

user7690392 | Posted in Energy Efficiency and Durability on

We are having a custom home built in cold climate, Zone 6a, with a walkout basement. The slab has 3″ PS foam under a 4″ slab with hydronic heat tubing near middle of that slab depth. Basement walls are mix of 8″ poured concrete and 2×8 framing. While I would have preferred interior insulation of the footings and slab edge, that didn’t happen. The contractor had previously installed 3″ foam on exterior of all concrete basement walls, but nothing similar was done for footing portion of the conventionally framed walkout walls. Of course there will be interior insulation, but slab edges of the walkout areas are uninsulated. So now we need to have excavate to add exterior rigid foam in areas that missed it. (My GC insists this will provide negligible benefits for heat loss and thinks it’s a waste of our money).

My question, which I didn’t see discussed in GBA articles or web resources, is about the ‘bang for the buck’ in how deep to dig along a stem wall exterior. My guess is that running insulation down ~ 1′ below the bottom of the slab would be a reasonable lower-cost compromise vs digging all the way down to the footings, and I’d welcome others’ thoughts on that. Figure B in attached diagram shows this best, except my slab insulation stops at the stem wall – the section where slab edges sit on stem wall ‘notch’ is uninsulated.

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.


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |