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Connecting Top Plates of Interior and Exterior Walls

mpsterner | Posted in Building Code Questions on

Hello all,
I am interested in running my 1.5″ 2×4 service cavity on the interior of my 2×6 wall straight around the perimeter of the house with no breaks. Also, keeping my Intello air barrier completely contiguous.

Typically, you would overlap the top plate anywhere an interior wall meets and exterior wall. Can I skip that and just screw my interior walls into my horizontally running 2×4 service cavity members? This would allow me to have my air barrier go up the wall and turn in at the ceiling with no breaks or penetrations.

I can’t find anything requiring you to connect these top plates in code.

I do not have any interior shear walls.


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  1. Expert Member

    Hi Michael,

    Would it be possible to get a sketch of the assembly? I'm having a hard time visualizing it from the words, I'm sure others probably feel the same and just skip over the question. Only trying to draw more attention to it.

    1. mpsterner | | #3

      Hey Kyle, I've attached a section drawing that shows the horizontal 2x4s as the service cavity.

  2. Expert Member
    Akos | | #2

    You only need a structural connection if the interior wall if it is a shear wall. Otherwise you can do anything that looks sturdy enough, it is only there to hold up drywall.

    1. mpsterner | | #4

      Okay, that is what I figured if it wasn't a shear wall since technically you don't even need to have the interior walls at all...

      This will make it easier to keep the interior air barrier completely unbroken and reduce the caulking/taping.

      Thank you as always!

  3. JacobTig | | #5

    Is this for new construction? The nice thing about having full height interior walls, built at the same time exterior walls, is ease of walkability for the framers when they’re putting up trusses/ceiling joists and rafters. Other than that consideration I think dropping the interior walls (presumably framed after roof is up) below the air barrier makes a lot of sense!

  4. SCChris | | #6

    Bomber wall. I’m planning on something similar.

    You can also frame your interior non load bearing non shear walls 3/4” off of your exterior wall and run your drywall continuous on the exterior walls. The service cavity 2x will serve as nailing/screwing in the end stud of your interior wall. Might be more of an ease of work in your situation but if your drywall was your vapor control layer this would isolate the control layer to an easily identifiable location.

    1. Expert Member
      MALCOLM TAYLOR | | #9

      "You can also frame your interior non load bearing non shear walls 3/4” off of your exterior wall and run your drywall continuous on the exterior walls."

      As long as you don't plan on running any services (electrical, vents, etc.) between the two. Interior walls always seem like a good place to terminate drywall runs to me. Otherwise you are likely to end up with more butt joints in the field.

      1. SCChris | | #11

        Touché! It’s a niche detail for sure

        1. Expert Member
          MALCOLM TAYLOR | | #12


          There's something very appealing about the idea. I'd love to figure out some variant that removed those drawbacks.

          1. SCChris | | #13

            It was a FHB article I read. I’ll keep an eye out for it

  5. Expert Member
    BILL WICHERS | | #7

    I see no problems with your detail in terms of structure, but I would make two changes:

    1- I would use a 2x4 at the top of the wall instead of a 2x3. This would give you a bit shy of an inch to attach drywall instead of a much smaller 3/8" strip that you'd have with a 2x3. The extra width will make it much easier to hang the drywall without blowing out the edge with the screws.

    2- I would use 5/8" drywall not only on the ceiling, but also on the walls. 5/8" drywall makes for a much more solid and flatter wall, and is also better for blocking sound transmission between spaces. I use exclusively 5/8" drywall on all of my own projects for these reasons.

    I recommend using 1.5" deep steel 4" square electrical boxes with mudrings to bring the devices up flush with the finished drywall surface. This gives you a commercial-style electrical installation and is also pretty easy to build with. If you use what I call "wing boxes" (the boxes with a welded-on metal wing that you can nail to studs), you can mount them with the wing either vertically on a stud, or horizontally on your 2x3 battens without worry -- the mud rings can be rotated 90 degrees so that you can always keep your devices oriented the way you want regardless of which way the box is installed. You can get mud rings to give you either one or two gang openings off of those 4" square boxes too.

    If you don't want to use steel boxes, my second choice is the white fiberglass "hard boxes". My last choice is the regular blue plastic boxes. You can get fiberglass and plastic mud rings for the nonmetallic boxes too, so you're not completely locked into steel boxes just because you want to use mud rings.


  6. mpsterner | | #8

    All really good feedback. I appreciate everyone's help!

  7. SCChris | | #10

    I checked your wall details but it cut out at the roofline. I don’t know which climate zone you’re in, which changes the relevance of my below comment:

    You’re running your rainscreen into the soffits. This could be a problem with ice dams in high snow load areas (snow’s an insulator, there’s snow on your roof but none on your walls) if you have an unvented roof assembly.

    This whole talk is amazing and worth the watch, but you can skip to minute 15 to see what I’m talking about

  8. user-6184358 | | #14

    Check the code - I think you need to brace the walls for a 5 or 10 psf force. The lowest seismic force I think is 1% of the weight for non structural stuff. That's what come to my mind right now, I don't have time to give exact references

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