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I’m in the process of building a master bedroom suite to our house, which is located in Oregon – marine climate.

Uz54hcdpsM | Posted in Energy Efficiency and Durability on

We have 2×6 stud walls that are presently empty but we expect to fill with fiberglass insulation, and 7/16 inch OSB sheathing covered with Tyvek Drain wrap. Soon, I intend to add a 3/8 inch thick furring strip to create a rain screen before installing Hardiplank siding. My windows have already been installed and flashed.

I’m interested in improving the performance of this wall; however, the professionals we hired thus far have disagreed with the idea as being cost inefficient and impractical. What are my options at this point?

I’ve read the articles about installing rigid foam to the exterior. Would installing one-inch, foil-faced, rigid foam to the interior surface of the 2×6 reduce vapor/thermal bridging issues? I would tape off the seams, and I’m familiar with the issue of extending electrical boxes and jambs. This interior foam would be topped be 1/2 inch drywall. Thanks for the advice.

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  1. GBA Editor
    Martin Holladay | | #1

    It's too bad that you didn't finalize the design of your walls before you got to this point. After all, once your windows are installed and flashed, it's a little late to think about where you want to put your rigid foam sheathing.

    The best location for rigid foam is on the exterior of your walls. To do it right, however, you would have to remove your windows.

    Installing interior rigid foam will work. Although it doesn't address rim joists or partition wall intersections, it will certainly improve the performance of your walls.

  2. mike eliason | | #2

    "the professionals we hired thus far have disagreed with the idea as being cost inefficient and impractical. "

    are you sure these were professionals?!?

  3. jklingel | | #3

    Given your constraints, why not just use a better insulation in your walls? I am not the expert here, but I'd wager that cellulose, cotton, or mineral wool batts would far surpass the real R value of the fiberglass. Too, you could wet spray in cellulose, or maybe it is not too late to dense pack the cellulose or that fiberglass Spider stuff I just learned about. I will never install another fiberglass batt. There is some good info on the Spider material here:

  4. Lucas Durand | | #4

    Another option might be to strap the interior of the walls horizontally with 2x3s then insulate with a blown in material.

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