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I am planning an addition where the lower floor will be at the same elevation as the existing walk-out basement, and will be left unheated as a screened porch. The upper floor will be supported on piers. At the perimeter of the lower floor there will be a concrete block knee wall 24″ high, which will rest on a concrete grade beam.
My question is this: will the slab (floating and isolated from the grade beams) get pushed around by frost? The masonry contractors I have spoken with say it will definitely move. I figure that with proper drainage and well compacted gravel underneath there shouldn’t be a problem. Even if I went with a full concrete block foundation to frost line (4 ft) with insulation on the perimeter and insulation under the slab, (as one contractor suggested) frost will still get under it. Is my only option to make it a suspended structural slab? Seems like alot of work for a screened porch.
Any insight you folks can give me would be appreciated.
Andy
Replies
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I am planning an addition where the lower floor will be at the same elevation as the existing walk-out basement, and will be left unheated as a screened porch. The upper floor will be supported on piers. At the perimeter of the lower floor there will be a concrete block knee wall 24" high, which will rest on a concrete grade beam.
My question is this: will the slab (floating and isolated from the grade beams) get pushed around by frost? The masonry contractors I have spoken with say it will definitely move. I figure that with proper drainage and well compacted gravel underneath there shouldn't be a problem. Even if I went with a full concrete block foundation to frost line (4 ft) with insulation on the perimeter and insulation under the slab, (as one contractor suggested) frost will still get under it. Is my only option to make it a suspended structural slab? Seems like alot of work for a screened porch.
Any insight you folks can give me would be appreciated.
Andy