Stem wall ledge for slab support
I’m leaning towards doing a slab on grade foundation with a stem wall for a new house, and have been thinking about slab edge insulation details. The most common approach seems to be to include a ledge, something like a brick ledge, on the interior of the stem wall. This ledge is usually wide enough to allow for up to 2″ of insulation at the slab edge, while still allowing for the slab to slightly overlap it.
For someone looking to increase the thickness of the slab edge insulation beyond two inches, the depth of this ledge becomes a limiting factor. So here’s the question: how important is having this ledge anyway? If this detail could be omitted, the foundation could be narrower, edge insulation could be increased significantly, and the foundation formwork could be simplified. Or you could easily use an ICF stem wall, with the slab supported simply by the compacted ground and appropriate insulation beneath it.
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