Does code allow an exterior stud wall to be cantilevered over rim joist?
New Hampshire, Zone 6a/ 1400 feet Elevation:
I am exploring a way to mitigate the thermal bridging at the rim joist of a double stud wall.
Does building code allow an exterior, load-bearing stud wall to ‘hang off’ the edge of the rim board? If so, I am hoping this would free up an inch or two to add rigid foam around rim joist and between bottom plate of stud wall and ICF wall. I am thinking either rigid mineral wool or Type II EPS for vapor openness in a cold climate.
I cannot locate this topic anywhere in the 2009 IRC code book- so I thought I would pose the question to the GBA community.
Here are a couple of links where I have seen it illustrated:
1. 2×4 double stud wall: (1″ of XPS)
2. 2×6 wall (2″ Rigid Insulation) (see Figure 2-13S)
Thanks, as always, for the help!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Sorry: Links appear to have disappeared:
1. 2x4 double stud wall: (1" of XPS)
https://www.greenbuildingadvisor.com/cad/detail/double-stud-wall-floor-truss-icf-foundation
2. 2x6 wall (2" Rigid Insulation) (see Figure 2-13S)
http://foundationhandbook.ornl.gov/handbook/section2-2.shtml
You can "overhang" 2" of a 2x6 wall, but the remainder 3.5" of the 2x6 wall is treated as the structural 2x4 wall. All size, height, spacing and load is calculated based on the "2x4" wall portion. Also, any floor or roof truss resting above this wall, should be calculated within the 3.5" continuous bearing and not with the 2" over the rigid foam section, and any header in this "2x4" wall must be framed on the inside of the wall, to form a continuous bearing to the foundation wall.
Rick,
Armando has it right.
Building codes do not prohibit framed walls from cantilevering over the foundation --- but all walls must meet basic structural requirements.
If you have any doubts about whether your detail meets structural requirements -- which in some regions of the country may include earthquake-resistant details or details appropriate for high wind zones -- you should consult an engineer.
Excellent- thank you Armando, Martin!