Insulating a stepped foundation from the interior
I have a basement room that I’m planning to insulate. It’s new 2×6 construction but the foundation is 15 years old. It’s in zone 6. It’s stepped with the west wall being half 8ft and half 4 ft of poured concrete, a south wall being 2ft and an east wall being a 1/2 ft off the floor. I insulated the exterior of west wall with 2in of XPS from the outside while digging it out for a drain. That wall had been getting wet, but is now very dry due to the drain work. I’ll also be building a wall to seperate the garage from the room and insulating above the garage.
There is a wood stove and a wall of south glazing in the room. I wasn’t planning on insulating the floor.
I am considering framing a 24oc inner wall from ceiling to floor which means the outer wall will be partially concrete. I’d use PT on the floor plate with sill seal under that. Making a 12in space to insulate with roxul or perhaps cellulose.
I don’t feel really good about burying the sill behind insulation. I like being able to see the sills in house, so my alternative is to roxul the 2×6 framed sections and puting an inner layer of 1in polyiso over the studs. Leaving the concrete heat sink and sill exposed for me to look at..
Any watchouts with my inner wall idea? Any feedback in general? A better way?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part