double-stud redux: detail on why inner-load-bearing is more complicated?
buildzilla
| Posted in General Questions on
inner-load-bearing obviously has better thermal properties by keeping rim-joists away from the exterior, but i’ve heard people say that they are more complicated and i seem to see them executed less frequently.
can someone who has witnessed both kinds framed, comment on the details that make inner more complicated?
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Replies
buildzilla,
There are so many variants it's hard to generalize, but some potential complications are:
- You usually have to make the foundation thicker to provide bearing for the inner-wall to carry structural loads.
- The sheathing often needs to be on the load-bearing wall, meaning you either need a second layer, or to go with the cladding or rain-screen furring directly on the studs, which makes cladding and trim more difficult.
- The sequencing can be a lot closer to what is typicality done when the exterior wall is load-bearing. You can frame fairly conventionally and then build the second wall on the interior.
- Depending on how the roof is framed, it may become a lot more complicated.
None of that means double-walls with the interior one bearing aren't a good idea - and there are countless variants to choose from that work well.
You don't need the complications of an inner structural wall to avoid the thermal bridging at the rim joist.
Most codes allow for the wall bottom plate to be offset 1/3 the width from the support. With a 2x6 load bearing wall, this lets you inset the rim joist 1 3/4" which gives space for rigid insulation there. The sheathing can span across this and connect walls and foundation.
When you say the sheathing connects walls and foundations, what is it attached to on the bottom? The mud sill? Or do you actually connect it to the foundation with Tapcons or something?
If it has enough shear strength I like the sound of it, bottom plate over mudsill, rim joist inset and 1-1/2" insulation against the rim joist and flush with the mudsill and bottom plate, then sheathing tying it all together.
Yup, that is what I was thinking, attach to the sill plate.