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Zone 5 metal stud wall with rigid

user-1125627 | Posted in Energy Efficiency and Durability on

I have a project with metal stud walls, gyp. sheathing, weather barrier and R10 EPS rigid in the cavity.  Then R10.1 closed cell spray foam in the stud space.  Brick exterior.
Part of the team calls for a normal, permeable weather barrier.   Part of the team wants an impermeable Permabarrier…either ok with the insulation setup?

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Replies

  1. Expert Member
    BILL WICHERS | | #1

    Spray foam is a waste in a wall with metal studs. Thermal bridging with metal studs is much more severe than with wood and it just kills the whole-wall performance of your insulation. Rigid foam is a big benefit here if used as sheathing, but there are more economical options than spray foam for the wall cavities.

    Bill

  2. Expert Member
    AKOS TOTH | | #2

    Your stackup ends up with something around R15 wall, most of your insulation R value is outside the studs, which gives you plenty of condensation margin.

    The question is more about water leaks behind the foam. The R10 cc SPF does have some perm rating, so you will get some drying towards the inside. A permeable WRB with EPS will also allow for some drying towards the outside, which feels like a more robust wall. I really don't see what an impermeable WRB gets you in this case but it should work as well.

  3. GBA Editor
    Martin Holladay | | #3

    Dave,
    Here's one more voice to let you know that the spray foam between the metal studs is virtually worthless. With steel studs, all of the the insulation needs to be installed as a continuous layer of insulation on the exterior side of the wall sheathing -- because thermal bridging through the studs negates the value of any insulation installed between the studs.

    You wrote that you have installed "EPS rigid in the cavity." I don't know what you mean by "in the cavity." If that means that you plan to install a continuous layer of EPS on the exterior side of the wall, that will work. Just make the EPS a little thicker, and skip the spray foam.

  4. Jon_R | | #4

    While you don't get good value from spray foam between steel studs, it certainly isn't worthless. For example:

    steel stud wall with .5" EPS on each side and air fill: R6
    steel stud wall with .5" EPS on each side and 2.5" CC spray foam fill: R14

    You probably want to fill with cost effective fiberglass (~R11 for the above wall).

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