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Community and Q&A

Double wall question

Keltomluna12 | Posted in Green Building Techniques on

Hi there. I live in New-Brunswick (eastern Canada). I’m looking to build a double 2 x 4 wall…studs staggered…separated by a 4.5 inch gap to fill with dense packed cellulose to achieve ~ R40. I’m doing it this way so as not to use materials that would be considered worse for the environment (such as rigid foam, spray foam, etc.). I’m wondering about which vapour and air barriers to use and where to place them in the “wall sandwich” so I don’t run into any problems. Any suggestions would be extremely helpful!

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  1. Expert Member
    Malcolm Taylor | | #1


    If you include a rain-screen cavity, which you should to allow your sheathing increased ability to dry, you can build the wall with an interior poly air/vapour-barrier that builders in your area are familiar with.

    Although not essential, if you want to upgrade to variable membrane instead, that will come with both a cost and labour penalty, but will improve the performance of the wall. Treating the sheathing as a secondary air-barrier by taping the seams and sealing the perimeter and any penetrations is another upgrade I would consider.

  2. Keltomluna12 | | #2

    Thanks, Malcolm that definitely helps...I was thinking from exterior to interior: rain screen/air/sheathing/cellulose/vapour/strapping/gyprock...does that sound right? The pro clima products look like they might be worth their exorbitant price but I'm not sure if that is going overboard.

    1. Expert Member
      Malcolm Taylor | | #3

      Talking about double-walls here usually starts a deluge of people suggesting their favourite variations, so be prepared!

      Strapping for rain-screen
      Tyvek Commercial WRB
      Plywood, taped as secondary air-barrier
      Poly, as air and vapour barrier
      (No strapping)

      I have no direct experience using a variable-perm membrane, so I'll leave comments on that to others.

  3. Jon R | | #5

    +1 on what Macolm said.

  4. MikeT1970 | | #6

    what wall assembly did you end up using?
    I am also from New Brunswick and am interested in a higher R value wall assembly.

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