This home uses ICF blocks for the foundation which provide continuous insulation around the foundation wall as well as serving as the formwork for the concrete core.
The wood framed walls are standard 2×6 with an additional 1.5 inches of rigid insulation on the exterior.
This forms a continuous blanket of insulation and is the maximum depth before the need for special screws, strapping, and engineering. The roof is super insulated with blown insulation.
This home uses as much additional insulation as possible without exceeding standard construction practices and incurring additional costs and expertise. It’s a smart way to build incrementally better without over stretching.