I'm currently working on design for a house in the southeast, on the border between climate zones 3 and 4 (officially 4). Tight site, 700sf footprint, 3 floors over a walk out, unfinished but minimally conditioned basement.
Wall composition isn't settled yet, though the minimum is likely 2x6 studs with blown cellulose or open cell foam and 2" exterior xps. Basement is possibly thermomass if the numbers shake out OK. Given the small footprint and envelope, I'm hopeful that we can opt for decent walls, roof, and windows.