How far below slab should footings be?
I’m trying to work out how many courses of ICF (16.5″ & 7.5″ heights available locally) I need to use for a walk-out basement foundation wall. The wall height is 9’3.25″ from the top of concrete to top of slab (small variation would be tolerable).
7 courses of full height ICFs would provide 115.5″ which would put the top of the footing 4.25″ below the top of the slab. Given that the slab is expected to be 4″ concrete over 2.5 rigid foam and 6″ gravel, is this sensible? Should the footing top be below the foam, for example? Should it be below the gravel?
Various combinations of the 16.5 & 7.5 blocks can produce a lot of total heights but obviously it’s less hassle to use 7 courses of full-height than 15 of half-height, for example.