To ledge, or not to ledge: that is the question
I am currently designing a home in Zone 5, an hour outside of Philadelphia.
Current foundation design is Slab;
8″ poured stem walls
2″ perimeter insulation
4″ horizontal insulation
15 mil vapor barrier
4″ concrete slab
The stem wall design does not have an interior ledge; the stem wall will be 8″ from the footer to the sill plate.
The exterior wall assembly is currently…
Zip Sheathing; 1/2″
2X6 Wall; 5 1/2″
8″ wall assembly can completely bear on the 8″ stem wall. Nice and Neat! Only the 1X4 furring strips (ventilation air gap) and Hardi siding would sit proud of the wall.
I made the decision to not include the interior ledge solely based on the responses to the same question posted on GBA.
” The ledge is an incidental by-product of thinning the top of the foundation so as to not have the intersection of the slab and foundation exposed on the floor. It is not intended as a bearing surface for the slab” -Malcom Taylor
Today I received the May 2019 issue of Fine Homebuilding. I truly enjoyed reading “Minimizing concrete in a slab-on-grade home” by Michael Maines, however, that same article has me rethinking the inner ledge of the stem wall. In the article, Mr. Maines details the foundation, which includes a built-in shelf, or ledge, to minimize potential settling of the floor system at the perimeter and included as insurance.
I would assume that providing a ledge for 6″ EPS would also warrant a ledge for a concrete slab, for good insurance?
To Ledge, OR Not To Ledge, That Is The Question.
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