Reason for Insulation on Interior Stem Wall
I see illustrations where rigid foam insulation is placed not only under a concrete slab and between the stem wall and the edge of the slab, but also vertically on the interior side of the stem wall. Often it’s shown going what appears to be several feet down the interior side of the wall.
I understand why it’s important to insulate under the slab and around the edge of the slab, but I can’t imagine why it’s important to insulate the interior of the stem wall. Please see the attached photo.
This photo was copied from the Building Science website, so I would consider that a reputable source.
I’m sure there’s a reason for it, but I can’t come up with it. Any help would be appreciated. I’m planning to build a garage in zone 4A (middle TN) that uses a concrete slab and short-ish stem walls. Trying to get all my important ducks in a row.
Thanks again.
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Hi Goose - you didn't get a reply here and I assume you've found your answer, but I tripped on this photo looking for a stem wall detail... this is to prevent the ground under the insulated slab from freezing (the frost wall gets the weight of the building to unfrozen bearing ground, but it's a great thermal conductor) and pushing up the slab at the edges. This also keeps the mass of fill under the slab a more stable temperature year round - a thermal mass. With no wall insulation, the floor at the perimeter will be colder in winter than the centre of the slab, as the rigid insulation is sitting on colder fill there than at the centre (insulation can't stop heat loss, only slow it down). If you have radiant in-floor heat, you'd loose a lot of energy around the perimeter.
I ended up moving the location of my building slightly, enough that a monolithic slab made the most sense. But I certainly appreciate you taking the time to answer my question.
Thanks again and have a great day.
david,
I'd never thought it through either. Appreciate the explanation.