Is a interior formed shelf to support floor joists in a poured concrete stem wall worth the extra effort and cost?
I’m building a single story house with a crawl space in climate 4C, seismic D1. In order to minimize the distance from finished floor to grade, the top of theTJI floor joists will be even with the top of the sill plate. I think there are two ways to do this: (1) pour a 8” thick stem wall, and hang the TJI’s from the sill plate, or (2) pour a 12” stem wall formed with a 6” wide interior shelf supporting an interior sill that the TJI’s would sit on. Option (1) is simpler and cheaper, but I worry about a less a robust floor support and possibly noticeable vibration; and there would be a thermal bridge with no rigid foam between the joists and the concrete stem wall. I’ll insulate with rigid foam between the joists, and have mineral wool on the stem wall exterior. Option (2) uses 8 cu.yd. more concrete, and costs an unknown amount to form the shelf; but eliminates the thermal bridge at each joist, and seems like a more stable floor system. Any suggestions?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part