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Community and Q&A

Connecting Inner and Outer Walls of Double-Stud Assembly

lacroixb | Posted in Green Building Techniques on

Newbie to GBA here!

I’m very interested in double wall construction in which the inner wall is structural and has plywood sheathing to be an air barrier and moisture retarder.  The one detail that I haven’t seen called out is how are the inner and outer walls tied together?  Is this merely a strip of plywood on both the bottom and top of the wall?

I’m looking at this graphic:

This detail seems to show the top of the wall has 1/2″ plywood connecting the inner and outer wall.  That makes sense, but the details for between floors is a bit less clear… is that a piece of 1/2″ plywood between the top and bottom plates of the adjoining floors, using a cleat on the inner/structural wall’s sheathing?  And anyone have details on the foundation tie-in?

Thanks in advance for your assistance.  This site has been an awesome resource – and I just went ahead and paid an annual fee to do my part to help support it.


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  1. Expert Member


    There are a few ways to do this. Probably the simplest, which also provides continuous insulation outside the rim joists at any floors, is to frame the exterior wall starting on the stem wall below and go right up to the top of the floor joists, then run the sub-floor out so that it is sandwiched in-between the top plates of the wall below and the bottom plate of the exterior wall above.

    1. lacroixb | | #7

      That makes sense for the foundation tie-in. Thank you for the description.

      And the top of the overall wall is also easy... just rip a piece of plywood to your overall wall thickness, nail in above the top plate.

      But the one piece I'd like clarification on is how to attach the outer wall to the rim joist between floors... (and is that enough support to maintain spacing between the inner and outer walls? Or does a tie need to be done more often?). Would one build one floor of outer wall several inches taller than the inner wall, so the top plate lands roughly in the middle of the rim joist, then again rip a piece of plywood, attach that to the top plate of the outer wall, then just use a cleat to attach the plywood to the sheathing at the rim joist? This seems it would work, but would just like others experience. It seems this would provide proper spacing between inner and outer wall as well as a fire stop as well as support for cavity insulation on the 2nd floor.

      Thank you for your input. I do appreciate it.

      1. Expert Member
        MALCOLM TAYLOR | | #8


        I have done a poor job of describing what I was suggesting. Let me try again.

        You frame the house much as you would a conventional one, with sheathed, load-bearing walls.

        The only difference is you locate them on the inner side of the stem wall below to leave room for an outer one, and you run your sub-floor out beyond the inner sheathed wall by say 6" or so.

        You then frame the outer walls continuously from the stem wall below to the underside of the sub-floor. The wall for the storey above sits on the subfloor directly above.

        So the outer wall has no rims-joist, and is continuously connected to the rest of the structure though the subfloor.

        The downsides of this double wall are:

        - Once you have moved your sheathing to the inner wall, detailing cladding and trim on an unsheathed outer one is more difficult.

        - You can't build both walls at the same time.

  2. GBA Editor
    Kiley Jacques | | #2

    Welcome to GBA, Brian. We are glad to have you as a member. I'm attaching a Fine Homebuilding article that includes the step-by-step construction process that Dan Kolbert and Ben Bogie use for double-stud walls, as well as an illustration that might be helpful.

    1. lacroixb | | #4

      Thank you for the link, but this is for a structural outer wall. I am looking for structural inner wall info specifically, as I want an air barrier on the outside of the inner wall.

  3. Expert Member
    BILL WICHERS | | #3

    Sometimes you just use extra wide top and bottom plates. The smallest way to do it, which is also easy to visualize, is to use 2x6 top and bottom plates and 2x4 studs. Every other stud is aligned to the opposite edge of the 2x6, so you end up with "inner wall" and "outer wall" studs connected by the wider-than-a-stud top and bottom plates. You have to be careful with your spacing to have sufficiently narrow stud spacing to support you sheathing and finished wall surfaces though.

    You can expand those top and bottom plates out to 2x10s or 2x12s, which allows you to either stagger the studs like you do with the 2x6 plates, or just put them opposite each other since the extra-wide top and bottom plates still allow a gap between the studs to act as a thermal break. For really, really thick walls, I've heard of people using ripped strips of 3/4" plywood as top and bottom plates, along with some extra framing for load bearing areas, but I've never seen such a build myself.


  4. AlexPoi | | #5

    If your inner wall is the load bearing one, what I've seen done is to put the outer wall on top of the foundation insulation (insulated from the ouside). Then connect both wall by nailing a strip of OSB between an inner and outer stud. This gives the wall a bit more racking strength and help keep the cellulose in place.

    In Europe, they have special TJI approved for wall construction. I wish we had that in North America, it would make double wall construction a bit faster.

    1. lacroixb | | #6

      Building the inner wall with regular stick construction techniques - and sheathing/taping it, then using TJIs as "Larsen Trusses" on the outside is certainly an option that is on the table for me as well.

      The general goal for me is to put the primary air barrier INSIDE the wall assembly. The exterior sheathing will certainly be the WRB (and I'd certainly ensure it's air sealed as well) - but I would like the primary air barrier to be on the outside of the inside wall. I do realize this means two sheathing layers - an inside (air barrier + vapor retarder) and the outside (WRB) - and there is a financial cost to this, but my peace-of-mind is worth it. And it seems to me this is a very solid, very long-term assembly that will certainly outlive me - which is the goal.

      I generally like this setup more than rigid, external insulation - but would love to hear other's experience and pros/cons.


      1. Expert Member
        MALCOLM TAYLOR | | #9


        If you want a deep dive into one of the builders who first used an inner-sheathed double wall:

      2. wastl | | #10


        You could go Mooney style outside, 24 OC in between and some Rockwool in the gap. Tyvek as WRB. If the horizontal stud is in the middle you have a good nail base for some horizontal sheathings.
        Mooney style is also rather ok in terms of thermal bridging.

  5. Expert Member
    PETER G ENGLE PE | | #11

    You can also use a membrane product as your air barrier on the outside of the interior wall, and sheathe the outer wall normally. This saves a layer of sheathing. That's one reason to make the outer wall the structural one - you can build the interior wall on the floor, wrap it, then stand it up in place and tie the air barrier to the ceiling using overlaps and tape.

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