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Ensuring a non-load bearing wall is as such (double stud wall)

maine_tyler | Posted in Green Building Techniques on

Simple framing question (I think) pertaining to double stud wall construction.
Should anything be done to ensure that the ‘non-load bearing’ wall is truly not bearing any load, such as making it a bit shorter than the load bearing?

The specifics are as follows: A garage with concrete stem walls and interior slab. The exterior wall is load bearing on the stem walls. The interior wall (to be built) will be resting on the slab, therefore should not be load bearing. The load is a simple trussed roof, 24′ oc.

It would seem that the interior wall would actually take more of the load if built to the same height as the exterior, as the bottom of the truss will hit the interiors at a shorter span. Do I just build them a bit shorter and make sure to air seem any gaps if the air barrier cross there?

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  1. GBA Editor
    Martin Holladay | | #1

    An interesting question. My answer: "Don't worry about it." In the case of a heavy snow load, the load path exists, so your wall will be fine.

    It's unusual to build a garage with double-stud walls, so I'm guessing (a) the garage will be heated, and (b) the garage is located in a cold climate. If my guesses are correct, don't forget to insulate the slab perimeter with vertical rigid foam.

  2. charlie_sullivan | | #2

    I would err on the side of caution and allow bit of space, maybe 1/4". If the inner wall took too much of the load, the slab could crack. Once it cracked, the load would transfer to the outer wall and everything would be fine, but a cracked slab isn't desirable, even if it's not detrimental.

  3. Jon_R | | #3

    The increased chances of differential movement between the inside and outside walls might influence your air sealing choices. For example, gaskets over sealant.

  4. maine_tyler | | #4

    Thanks all. It is currently a garage but will become a heated wood shop. Vertical rigid insulation is indeed going around perimeter of stem walls. I am in climate zone 6a (Maine).

    Jon, for clarity, what is it that "increases the chances of differential movement"? Is it if I make the inner wall shorter? Build them the same height? Or is that beside the point and it is simply inherent with double studs under a trussed roof?

    For what its worth, my plan is to use Intello plus, wrapped over the top plate (from the exterior of the interior wall) onto or across the ceiling. So I will not be relying on gaskets or sealant at the top plate anyways.

  5. Jon_R | | #5

    If I understand correctly, you have a floating slab and a separate stem wall. Since they are at different depths and experience different loads and moisture changes, it's likely that they will rise or fall at different rates. But I think floor to wall to ceiling to wall to floor Intello can air seal well even with such movement.

  6. maine_tyler | | #6

    Thanks Jon. Yes you are correct.

  7. Expert Member

    I'm having trouble understanding how moisture levels in the walls or elsewhere would cause either foundations or slabs to move at all. it certainly isn't something I've ever seen addressed on any drawings I've worked from.

  8. Jon_R | | #8

    OK, it would be clearer to write "different moisture changes beneath them". Soil expands with moisture - how much depends on the soil.

  9. user-6184358 | | #9

    Make sure the truss mfg know about the double stud wall. The set the bearing condition at the ends when designing the truss. Do what they set as the bearing condition. They may require a gap to the inside wall to prevent loading at a non bearing point.

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