A hybrid Swedish-ish/Pole Barn-ish Wall Assembly?
I’m working through the wall assembly plans for a Climate Zone 4 home in eastern Tennessee.
NREL has several papers about condensation control in high-R value wall assemblies, often suggesting that up to 50% of the insulation value should be on the exterior of the sheathing in the winters even in CZ4 if interior relative humidity is high enough.
NREL WUFI analysis where every wall fails and we’re all going to die from mold (even the author asks what WUFI is smoking to reach these conclusions):
NREL water content percentages based on exterior/no exterior insulation and indoor relative humidity, including CZ4:
I like the recommendations of the whole wall R assembly recommended by Building Science Corporation and NREL:
Vented Attic: 60
Unvented Attic: 45
Basement Walls: 15
Subslab/slab edge: 7.5
This was long before COVID, where they believed these to be the most economical numbers, but 2″ of the cheapest foam insulation used to be $28 and is now $40 around here.
So I’m wondering if a wall that takes notes from some Swedish factory built homes:
and from insulated pole barns, for examples:
Hansen Pole Buildings:
So here’s what I’m thinking, and wondering if it’s an assembly that wouldn’t cause any mold issues. From the inside out:
– Vapor open paint
– 1/2″ drywall
– 2×4 @ 24″ O.C. studs, filled with R-15 Rockwool batts(or R-15 fiberglass)
– 7/16″ ZIP Sheathing (or maybe just regular OSB with seams taped?)
– 2×4 @ 24″ O.C. horizontal scaffolding, filled with R-15 Rockwool batts
– House wrap, seams taped
– 1x vertical furring strips
What I like about this assembly:
– It keeps the sheathing between layers of insulation.
– It’s easier to build than an interior structural wall that’s sheathed and then an exterior insulation double wall, because no one here does dense-packed cellulose.
– It’s a lot cheaper now than exterior rigid insulation board.
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