Hello. I will be building my home using ICF construction for the exterior walls. The basement will be 8" concrete and the first floor will be 6". The blocks use 2.5" foam on both sides. This is a single story house in Virginia (4A). The roof is a gull wing type standing seam roof with a 12:12 pitch in the center and something lower on the sides. The center of the house with the steep pitch has a cathedral ceiling and 4' knee walls facing attic space down the lengths. Since the house exterior will be well insulated with the ICF, I want to make sure the ceiling and knee walls match. I've tried to do my research and have cobbled the following together. I'd like thoughts and opinions if this is going in the right direction. I'm trying to get the best bang for my buck on this. I haven't found many folks familiar with an unvented roof and it seemed like the synthetic underlayment the metal roof would prefer would make me want to keep the roof vented. With that in mind, the cathedral part would be furred out to 2x12 for R38 insulation with baffles. Foil faced polyiso foam boards would be used on the interior before the drywall. I was thinking maybe 1.5 or 2" and then furring strips for the drywall. If this is a good approach should the baffles be sealed or is that creating 2 vapor barriers? For the knee walls, I was thinking of using 2 or 3" foil faced polyiso foam board as a backing for the batt insulation and then furring the cavity to at least 2x10 for R30 batts. The flat ceilings in the attic would be flashed and filled to R60 blown insulation. All total the cathedral part of the ceiling is a 1/3 of the sqft of the hosue. The knee wall is about 450 sqft total. It seemed like even with the foam boards, this was the most cost effective approach. I might be missing something though. I'd like to hear what others think or have done. Thanks!