I’m just playing around with a couple ideas here. I’m not a builder or engineer. Attached design is for a Zone 6, high-performance, two-story house my parents might build on their property one day.

Most notably, it uses balloon framing for:
– Simplification of air-sealing, vapor-sealing, and insulating details around the band joist (no spray foam),
– Better thermal performance (I’m guessing) around the band joist,
– Stronger walls (from what I’ve heard).

A service cavity to:
– Protect the vapor barrier,
– Eliminate air-sealing details around services,
– Allow a thermal break at foundation/floor slab interface,
– Provide additional insulation.

I know floor slabs aren’t in vogue right now, but I think this could be adapted to a concrete-free slab without too much difficulty.

Obviously would be more work getting walls in place, but it seems to solve a lot of the finicky work that goes into air-tight building. So, why have I never seen this assembly before? Apparently in Sweden and probably other European countries it’s somewhat standard. At least in American residential construction,  it’s either double-stud (looks more complicated to air-seal and insulate, especially by joists) or lots of exterior rigid foam (too expensive mainly). Is balloon framing really that hard to construct?