I am constructing an ICF house (Basement and primary floor ICF to the level of eaves). It will have a cathedral ceiling with an open half loft. I have checked out the “Cathedral Ceilings that Work” post what I was thinking about doing is generally a modification of “Assembly # 1” as laid out by that post.
What I would like to do is have a total thermal envelope of your home where the ICF walls, gable end walls, and roof sheathing create the envelope. I read an article about a house being built in this manner and enjoyed an accompanying YouTube video a while back however I didnt wait and I can not discover it for the life of me now. However basically they utilized Zip Sheathing which came right to the corner of the ICF absolutely no overhang on gable or eave walls. All seams were taped and whatever was insulated inside to create an extremely tight thermal envelope. Then above that 2x4s were placed on edge (with long timberlocks down into the rafters through the zip) to produce both an air space and the overhang framing for appropriate overhangs.
Another significant distinction from the “Assembly # 1” is that I was considering utilizing Dense Load instead of fiberglass batt.
The 3rd difference is that “Assembly # 1 ″ uses 2x4s gusseted onto the primary rafter for a much deeper cavity. Rather than do this. I was thinking that if I used a 2 × 6 and sistered it onto the side of the rafter, (overlapping 1.5”) rather than in line with the rafter with plywood gussets, and utilized dense pack it would efficiently create a thermal break because insulation would be stepped over the edge of the primary rafter and behind the include on extension if that makes good sense.
Am I missing out on any reason this wont work well?
Attaching a drawing for clarity. Drawn around to scale where 1 chart block=1 inch