As net-zero energy and Passivhaus-certified houses become more commonplace, it’s not at all unusual to hear of exterior walls rated at R-40 or R-50. But that’s not going to be nearly good enough for Tom Schmidt, who’s building a 3,800-square-foot house in Minnesota.
R-80 is more like it, and the walls need to be “cost-effective” as well as not too thick.
Schmidt’s quest has apparently been prompted by a design that places living space over a garage. According to Schmidt’s Passivhaus consultant, this configuration brings with it some energy penalties and results in the need for additional insulation.
“We have already gone through a couple passes to make it as efficient as possible and are at the point where the only change left that would have a big impact would be to take the garage out from under the living area and have it separate,” Schmidt explains in a post at GBA’s Q&A forum.
“I like the current design (it took us two years to get to this point between the back and forth with my wife) and I want to have the house certified. I could pass on the certification and still have a very high-performing house, but honestly I think it’s cool and want it.”
Schmidt says he has investigated a number of options and is currently leaning toward structural insulated panels filled with expanded polystyrene (EPS).
“Vacuum insulated panels sound interesting, but I don’t know if they are meant for an entire external envelope,” he adds. “The goal is to still keep it cost effective. I just don’t want a 3-foot wall to do it.”
Are Schmidt’s goals achievable? And even if they are, are they reasonable? That’s the topic for this Q&A Spotlight.