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Insulated header design

AR_Lilly | Posted in Green Building Techniques on

We’re building a small house in North Idaho (climate zone 5). 2×6 exterior walls with most headers being built of double 2x’s. Planning to insulate them with 2”EPS. The options I’m considering for this are:
1) Double up the 2x’s, nailed together and set flush to the outside, 2” EPS on interior with 1/2” air space between EPS and drywall; or
2) Sandwich the EPS between the two 2x’s (joined with 5” lag screws from both sides) with half inch gap between innermost 2x and drywall. 
Both header assemblies would have a flat 2×6 nailed to the bottom. I’m also planning to air-seal interior walls with ProClima Intello Plus vapor-variable air barrier membrane. 
My question is is there a reason, (structural, moisture, performance, or otherwise) to choose one method over the other? I’m an owner/builder and not concerned with labor cost, mostly just don’t want to waste energy or grow mold in the walls. Thanks!

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Replies

  1. Yupster | | #1

    A header is stronger joined together and many building inspectors in our area require they are built that way. Putting the foam to the inside helps prevent drywall cracks sometimes caused by shrinkage of the 2x lumber. Just make sure you put a plate under the header for a nailing surface.

  2. Expert Member
    MALCOLM TAYLOR | | #2

    Adam,

    https://www.jlconline.com/how-to/insulation/insulated-headers_o

    I'd add:
    - The advantage of having the header flush with your interior framing is that you can use it as backing for trim and to attach supports for window coverings.
    - Putting the foam to the interior is easier in terms of the sequence of construction, as the insulation can be added when the framing is complete.
    - Sandwiching the foam makes for a less strong and stable header. My reading of our code doesn't allow the wood members to be separated.

    That said - all three methods are regularly used without apparent problems.

    1. RussMill | | #3

      Ours have always been separate, funny how different things are from one location to another

      1. Expert Member
        MALCOLM TAYLOR | | #4

        Russell,

        A lot of what we take as necessary, or at least good practice, turns out to be very regional when you look at how things are done elsewhere. Some of the makes sense as adaptations to local conditions, but a lot is just habit or custom.

  3. AR_Lilly | | #6

    Thanks for the replies everyone. I ended up going with the 2x’s doubled up on the outside, 2” EPS inside of them, with a 2x6 plate (nailing surface) on the bottom. I figured structural probably most important, followed by energy. I do wonder still about the moisture considerations for the assembly; I.e., does the position of the foam layer change/alter the temperature and/or location of the “condensing surface”? And does this even matter that much if you’re air-sealing from the interior (and exterior) of the wall assembly?

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