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Community and Q&A

Insulation Retrofit

cwc09 | Posted in Energy Efficiency and Durability on

I am in the process of buying a 1,400-square-foot home in Zone 4 (mixed humid climate). The existing wall section is: brick veneer, 1″ air gap, tar paper, plywood sheathing and 2×4 walls.

Most of the deep energy retrofits I have researched include installing exterior rigid insulation, which is probably out of the question for me given that I would either have to tear the brick down or bury it under the insulation and new cladding. So I am considering creating a double-stud wall on the interior at a total depth of 10″, then filling with dense pack cellulose and airtight drywall.

I think this allows the best opportunity for substantial R-value and drying potential to the interior and exterior. (If I’m wrong please let me know).

My question is mainly how to approach air sealing before insulation. I am trying to avoid spray foam but would it benefit me to flash the stud cavities first? Or maybe just around the perimeter of the cavity?

I don’t think a fully flashed stud cavity would allow any drying to the exterior which is recommended in my climate (as well as to the interior). Any recommendations for air sealing from the interior or issues with the other details provided below I would greatly appreciate the feedback.


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  1. GBA Editor
    Martin Holladay | | #1

    If you want, you can install a layer of closed-cell spray polyurethane foam on the interior side of your wall sheathing, following the flash-and-fill method. If you go this route, be sure to install a minimum of 2 inches of closed-cell foam. This will provide effective air sealing.

    However, you wrote that you are trying to avoid spray foam. That means that your home is a good candidate for one of the new sprayable caulk products. For more information, see Air Sealing With Sprayable Caulk.

    If you are planning to install a double-stud wall on your home's interior, don't forget to air seal and insulate your rim joists. You need to come up with a plan to insure air-barrier continuity and thermal barrier continuity, from your foundation to your walls to your ceiling.

  2. cwc09 | | #2

    So the closed-cell spray foam wouldn't be an issue as far as allowing the wall to dry to the exterior? I am in a mixed-humid zone (Baltimore,MD).
    I am a general contractor working mostly in the residential remodeling sector for the past 15 years. I don't have any experience installing the "do-it-yourself" foam kits but would love to try and am willing to do it on my own property for this flash and fill scenario. Any recommendations (brands?,etc...) or issues with this (leave it up to an installer,etc....)?

  3. GBA Editor
    Martin Holladay | | #3

    If you decide to install closed-cell spray foam in a flash-and-fill job, the spray foam becomes the dividing line between what dries to the exterior and what dries to the interior. Everything on the outside of the spray foam -- namely the plywood sheathing, the asphalt felt, and the brick veneer -- dries to the exterior. Everything on the inside of the spray foam -- namely the studs, the cellulose, and the drywall -- dries to the interior.

    Needless to say, you can't install interior polyethylene on such a wall.

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