Colleen A, planning a new house in Michigan’s Climate Zone 5, has discovered there’s a downside to the wealth of insulation products on the market: It’s hard to make a decision.
“There are so many options on exterior insulation that my head is spinning,” she writes in a Q&A post at GBA. So far, her research has led her to an exterior wall assembly that includes a 2×4 framed structural wall filled with 3 inches of closed-cell polyurethane foam, oriented strand board sheathing, 1 1/2 inches of extruded polystyrene rigid foam, and Tyvek DrainWrap as a water-resistant barrier.
She’s considered other possibilities, including a 2×6 framed wall, Roxul mineral wool insulation, and polyisocyanurate rigid insulation. There are drawbacks to all of them.
And then there’s the issue of building industry inertia, the difficulty of finding local builders as interested in the topic as she is.
“We will be our own contractors for the house,” Colleen writes. “I haven’t found any local builders that specialize in energy efficiency. From anyone I’ve talked to so far not many are interested in doing above and beyond code and seem to think it’s a waste of time and money. I don’t think so.”
Colleen’s questions are the topic for this Q&A Spotlight.
Exterior insulation is the right idea
Colleen is on the right track with exterior insulation, writes GBA senior editor Martin Holladay, even if some of the details in her wall assembly are less than ideal.
“Installing a layer of rigid foam on the exterior side of a 2×6 wall is a good idea,” he says. “This will increase the R-value of the wall, reduce thermal bridging, and reduce air leakage.”
But, he adds, installing spray polyurethane foam in the stud cavities is not a great…
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