Maison Grande-Digue House is designed with double 2x4 insulated, exterior stud walls @ 24" o.c. separated by a 3-1/2 inch fully insulated space to isolate the exterior walls from thermal bridging. The outside double stud walls would be erected prior to construction and erection of the interior partition walls. The inside stud walls are designed to be load bearing while the outside stud walls are designed to carry the exterior finish. The cold side of the inside stud wall is completely covered in a 6 mil vapor barrier then sheathed with 1/2 inch CDX plywood sheathing to provide lateral bracing as well as protect the vapor barrier.
Red dashed line shows location of the 6-mil vapor barrier in the wall system. Red dots show locations where barrier is sealed with acoustical caulking.
Experience has shown that the vapor barrier can be safely installed inside the wall as long as 2/3 of the insulation is on the cold side of the barrier. Locating the vapor barrier at the cold side of the inside stud wall allows for installation of electric without penetrating the vapor barrier. The cold side of the outside stud wall is sheathed with 1/2 inch fiberboard sheathing, then covered with house wrap. The design allows for the walls to be framed and insulated on the floors and lifted in place using wall jacks. A perimeter truss with 2x4 vertical blocking in line with the 2x4 wall studs above is required to carry the loads to the foundation. Details for optional balloon framing and openings are provided in the links and will be discussed later.
The Maison Grande-Digue House foundation walls are formed using LOGIX insulated concrete forms. While not a fan of rigid insulation, insulated concrete forms do have their place in the design of a foundation. The two layers of insulation used in the ICF system provides R20 insulation for the basement plus facilitates installation of finishes both inside and outside as well as easing reinforcing placement. The concrete foundation walls also create an effective vapor barrier. Care should be taken in laying out the exterior dimensions of the building and height of basement walls to match the dimension of standard ICF components (standard LOGIX block is 16" high x 48" long x depth desired). The 12" x 24" footings are the standard architectural overkill. Adjustments are feasible based upon engineering for local soils and conditions.
As mentioned in an earlier posting, crawl space and slab-on-grade foundations are also feasible, but space must be made on upper floors for mechanical equipment. See links to construction details for additional details and foundation systems.