In your Edelweiss house you use 2x6 studs. Why not use 2x4 studs and add 2" rigid on the inside?
8" semi rigid and 5 1/2" between the studs. why not use 8" semi rigid, 3 1/2" between the studs and 2 " more semi rigid on the inside beneath the gyprock? Is that possible?
2x4s can be used for homes no problem, but it definitely fattens up the posts required between windows. The sections of wall between the south-facing windows in the Edelweiss house are fully filled with 2x6s, and would have been much thicker if the structure were made out of 2x4s. Designs with higher levels of glazings are often 2x6 for this reason. The best is to drop the large windows and go for smaller openings, but the building site was just begging for that sweet forest view in our case, so with the view and solar gain in mind, we have no regrets. Great question to bring up, thanks!