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Opinions on This Wall Assembly Plan

LizNH | Posted in General Questions on

We’re renovating a 1985 house in Conway New Hampshire and the existing wall assembly is:

1/2 Drywall
Sheet of Polythene directly under drywall
R-11 Fiberglass insulation with Kraft Facing
1/2 plywood
WRB – not sure on brand yet
Painted Cedar Shingles – that will be removed as part of renovation and probably replaced with LP Smart-side Lap and board and batten.

As part of the renovation we are reframing some of the exterior walls for new windows that are in different locations and different sizes.  At most we are opening up 5-6 feet of wall space in a few different rooms.

Should we include the polythene and seal with acoustic caulk or leave it out?  Use Kraft faced insulation or use unfaced?  On one hand the walls that were opened up so far were nice and dry and looked good and so we think since we’re not opening all the walls, that we should stay consistent with existing assembly. On other hand, I thought polythene was a risky vapor barrier, should we go with something else?   Any thoughts on siding or which WRB when we reside the house? I was thinking a drain wrap might help a bit.

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  1. GBA Editor
    Kiley Jacques | | #1

    Hi Liz,

    I’m giving your question a bump. While you wait for experts to weigh in, this article might help inform your plan (or at least make for interesting and pertinent reading): Five Walls that Work.

    1. LizNH | | #4

      Thanks for the bump and the link, I'll check it out!

  2. Expert Member
    BILL WICHERS | | #2

    If your local codes don't require polyethylene, leave it out -- poly in walls can cause moisture problems. If codes require poly, see if you can use a smart vapor retarder like MemBrain or Intello instead, which are safer.

    The kraft facing of the batts is already a vapor retarder if installed properly. I personally prefer to use mineral wool batts (or high density R15 unfaced fiberglass batts), and a seperate vapor retarder (usually MemBrain) over the entire interior of the stud wall though.

    I would use urethane caulk for sealing, not acoustical sealant. Acoustical sealant is incredibly messy to work with, and it stays messy forever.

    I would recommend using 5/8" drywall instead of 1/2". 5/8" is the commerical standard, typically costs less than $1/sheet more than 1/2" drywall, and it will give you flatter walls, better sound reduction, and an overall more solid wall assembly. It's really amazing how much of a difference that extra 1/8" of drywall thickness can make in a wall.


    1. LizNH | | #3

      Great info, thank you! I'll check with the local building official, he has been reasonable and helpful so far. I like the idea of a vapor retarder verses the poly vapor barrier. I was concerned about having the two systems in the same where we had torn out everything to reframe and then the next door room being left untouched. I suppose as long as they are separate stud bays, we should be ok, right?

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