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Community and Q&A

Eliminating Interior Vapor Retarders

brad17 | Posted in General Questions on

We are designing houses in 3 different climate zones: 4A, 5A, and 6A and are getting push-back from builders in all three locations about using something like Intello Plus on the inside of our walls. Does anyone have an opinion about whether eliminating this layer will be an issue? Our walls are generally 2×6, with rockwool batt, with enough continuous insulation outside to avoid wet walls in each location and proper rain screens.

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  1. the74impala | | #1

    Do they want to use Poly, or nothing instead of Intello. They clearly don't know what Intello does if they think it will cause the house problems.

    It will cause them problems if they don't like learning new things though.

    1. brad17 | | #3

      Thanks Tom. They are generally used to not adding this layer at all. They don't think it will cause performance problems, but rather that it adds cost and labor that they feel isn't entirely necessary if the wall is properly air sealed and well designed.

  2. Expert Member


    Have you checked what your building code says about the necessity of including them in those zones?

  3. pnwnerd | | #4

    Just curious, how much continuous insulation do you plan?

    1. brad17 | | #6

      Zone 4A: R6
      Zone 5A: R6
      Zone 6A: R6 Comfort Board 80 or R12 rigid foam

  4. brad17 | | #5

    Zone 4A: R6
    Zone 5A: R6
    Zone 6A: R6 Comfort Board 80 or R12 rigid foam

    1. Expert Member
      Akos | | #7

      Take a look at here:

      Zone 4, R6 is fine with just painted drywall (class III vapor retarder)
      Zone 5 and 6 you need a bit more insulation or class II or better vapor retarder

      Craft faced batts are class II and would work instead of poly or intello.

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