Basement insulation with different slab levels
My proposed basement has 2 levels and I am trying to finalize the details to insulate where the 2 levels meet. I am planning on insulating the perimeter walls from the inside. However, where the floor levels change I am contemplating insulating under and around the footer, and then up the sides of the foundation wall to the top of each slab. The assembly from top down is 4″ concrete, vapor barrier (not shown), 4″ of EPS type IX, 4″ of 1/2″ clean stone, undisturbed earth. The footer is 30″ wide x 12″ and the foundation wall is 12″ wide, standard size around here. There is a capillary break between footer and foundation. See attached detail.
Thoughts?
Thanks.
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Replies
Jonathan,
It doesn't look like the short vertical concrete wall in the illustration is supporting a load, so your proposal is fine -- as long as you don't have an engineer involved in your project who freaks out about foam under a footing.
If you simplify the details by leaving out the foam under the footing, the amount of heat loss would be fairly insignificant. This is near the center of your house, after all, not at the perimeter (where the soil is colder).
Thanks Martin. There is no load at that wall as you surmised. There will be a railing and steps down to the lower the section.
The footing & stem wall is really just a retaining wall then?
Resting the upper slab on top of that wall is likely to result in cracking the slab. It's probably better to mechanically float the slab, supported only by the foam & compacted soil, with a expansion joint between the retaining wall and the slab. The top of the retaining wall can be at the same level as the slab, but if anything shifts or settles over time any imperfections in the finish floor will be along the line of the expansion joint, not shooting off in a random direction.