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Double walls with different heights?

Jerry Liebler | Posted in General Questions on

My latest sketch has double 2×4 walls with the outer wall supporting itself and the roof while the inner walls is supporting the ceiling (framed with 9 1/2″ I joist 24″OC) , an attic floor (the air barrier) and insulation. This allows deep insulation with flat bottom trusses and gives an “attic” floor to “set” the trusses. The ceiling service cavity below the air barrier allows “can lights” without the usual leakage issues. Hopeully the flat bottom trusses will be enough cheaper than deep energy heel trusses to offset the cost of the I joist. Has anyone done something similar?

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Jerry,
    Carl Seville installed an attic floor and used it as his ceiling air barrier, and then set his roof framing above the attic floor. Read about it here: Topping Out.

  2. User avatar
    Stephen Sheehy | | #2

    I'd price raised heel trusses. I was amazed at how cheap our trusses were. I think you can save money by placing your airbarrier against the bottom chord and putting 2x4 strapping below it, using the 1 1/2" space as a wiring chase. Of course, if you need the chase for hvac stuff, you'll need more room.

  3. Malcolm Taylor | | #3

    Jerry,
    There are a number of good reasons to include a flat roof deck below trusses, but having somewhere to set them from isn't one of them. A crew of three should be able to set the trusses for a house in a day without a floor to work from.

  4. Bob Irving | | #4

    We use LED surface mounted lights instead of the old fashioned cans. They work just like the cans, but at 1" high, can go within the ceiling strapping and below our Majpell air barrier affixed to the bottom of the trusses. No more dealing with air leakage from cans.

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