Double Stud Wall with Mineral Wool Batts
We have settled on a double stud wall design for our new house. We had planned to use dense pack cellulose to fill the cavity, with a goal of an R40 wall. Unfortunately, we’ve only been able to find one firm in our region (Billings, MT) that does dense pack cellulose and they’ve never done a twelve inch cavity like we are proposing. They are willing to try, but having read a few warnings on GBA about finding contractors experienced with dense pack, we’re looking at other options.
Wanting to stay with the double stud wall design, we have looked at mineral wool batt insulation as an option. It seems like we could run mineral wool vertically in the outside 2×4 stud wall, run 5.25 inch batts horizontally in the space between the stud walls, and then run batts vertically again in the inner 2×4 stud wall. I’m unsure how to calculate the true R value of this wall, but based on the mineral wool packaging it would be R15 + R23 + R15. We recognize the true R value would be less than R53, but would it be R40 or greater?
Any other thoughts on this approach? Pitfalls? Concerns? Tips?
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