Architect’s question: Plank house insulation
My client is renovating a “plank house” in Zone 6 (west central NH). The house is timber framed with 2″ thick vertical wood planks outside of the frame for exterior walls. There is 1″ (actual) thick wood sheathing on the exterior of the planks (so a total of 3 inches of solid wood). Interior lath & plaster or wood paneling has been removed.
The owner wants to frame 2×4 walls with spray polyurethane foam on the inside of the planks and put 1″ rigid insulation board (not sure which variety) on the exterior.
I have expressed my concern to him that 1″ is inadequate in our climate zone, and that with vapor impermeable insulation on each side of the wood structure he may be creating condensation issues. However, my exposure in the field and at Better Buildings by Design conferences has been with standard framing, not plank construction. I do not have energy modeling software to analyze this wall system. Any input would be appreciated. Thank you.
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