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Community and Q&A

Options to make space for exterior insulation

user-5530971 | Posted in Green Building Techniques on

This is my first post so thanks in advance for any input. I’m finalizing the plans for our new home with in Kentucky, and I’m talking through the option of adding 2” of Roxul Comfortboard on the outside of ZIP wall sheathing with the builder. He has never done this before, and one of the objections he is raising is that it would require making the foundation/basement walls 2” thicker to make room for this since we are already planning on a brick cladding. Is that how space would typically be made for the exterior insulation when brick cladding is being used, or are there better alternatives? Below would be the wall layers from outside in:

¾” air gap
2” Comfortboard
ZIP sheathing
2 x 4 standard framing with blown in blanket insulation

Thank you,

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  1. Reid Baldwin | | #1

    How thick were the foundation walls intended to be without exterior insulation?

    The attached file shows how my house is built with 2" of foam and 10" foundation walls.

  2. user-5530971 | | #2

    Thanks Reid. This diagram is perfect to help me visualize how floor joists, sill plate and foundation walls come together. His foundation contractor pours 10" walls so looks like it would all fit perfectly without increasing the thickness of the foundation walls. I will show this to him along with Roxul Comfortboard installation guide. Thanks again!


  3. whitenack | | #3

    We just finished framing our house in central KY, and we are going with a brick exterior and 3" of exterior foam. Our contractor made the adjustments to the thickness of the foundation walls and no one batted an eye. It obviously takes more concrete, but it is not difficult for the concrete subs to make those walls a little bit thicker.

  4. user-5530971 | | #4

    Thanks Clay. Was the original thickness 10" then they added 3" to make it 13"? Or maybe did they just add 1" and there was enough space for the other 2" in the original thickness of the foundation as shown in the diagram that Reid posted?


  5. whitenack | | #5

    Was he planning a block wall, or poured concrete?

    Not sure what the original thickness was going to be. And I can't remember if they are 13" or 12" walls. I know there is one wall that is 16" or 18" thick because he wanted enough room to set two floor structures on it (one on each side), and wanted enough room. I remember them having a discussion about needing special ties for this thick when they were putting together the forms.

  6. user-5530971 | | #6

    Ok, thanks. He is planning on a poured concrete wall.

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