Mhenson has broken ground on a new house in the Colorado mountains, and he’s having second thoughts about his plans to use double-stud walls, a construction method in which two framed stud walls are separated by a gap with the entire assembly filled with insulation.
“I have done a lot of reading and had settled on double-stud walls until I read a couple of articles that said they may be risky,” Mhenson writes in this recent Q&A post. He worries that moisture may accumulate in the wall cavities, so he’s switching gears and now wants to use a wall with a continuous layer of foam insulation on the exterior.
The house will be at an elevation of 10,500 ft., and while it’s a high-altitude desert it’s still wetter than most of the state.
“My framing contractor is not a fan of this over the double-stud wall,” he adds. “Time is of the essence. Can someone set me straight on what is now considered to be the best method? Especially if neither of these is best!”
So what’s it going to be? A double-stud wall, or exterior foam over a conventionally framed wall? That’s where we start this Q&A Spotlight.
Risks are ‘mostly theoretical’
Malcolm Taylor believes that although there are theoretical risks of moisture accumulation in double-stud walls, “it doesn’t seem to be occurring in practice.”
Taylor refers Mhenson to an article Ben Bogie wrote for GBA, in which he refers to the moisture potential of double-stud walls as the “yeti of building science”—a beast of myth not reality.
That said, Taylor recommends that Mhenson make sure the assembly is well air-sealed, and that it includes a rainscreen to promote drying to the exterior.
Taylor adds: “Both double-stud walls…
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