sub slab and basement insulation – GreenBuildingAdvisor

hi- looking to rebuild my house and want to end up with a high performing build, close to passive as possible. Trying to educate myself and every turn is a brand new question.

I live on the northern part of the Jersey shore, between a couple rivers and few miles from the ocean. Climate zone 4a. Unfortunately the town has a major problem with variances so trying to not encroach on anything more than what I currently have. 

Looking to maximize continuous external insulation with a monopoly style build and an over-roof. For the exterior wall looking to have the conversation with the architect of the pro/cons of 2×4 framing, plywood, blueskin vp100, 5″ comfortboard, isolated hangers, 3/4 furring, hardy board vs 2×6 framing, plywood, blueskin vp100, 3″ comfortboard, 3/4 furring, hardy board. Of course comfortbatt in the interior cavity. We keep our house humid due to a baby grand piano/guitars/kids eczema so a wall that can pass vapor and then control with dehumidifier/humidifier seems to be best to minimize condensation which I am fighting right now.

But here’s my question — Our water table is 6ft and soil architect said footer at 4ft. I would like to put in sub slab insulation. In this scenario is comfortboard too close to the water table and therefore need to go to XPS? What depth is the insulation placed relative to the footer? In my mind you would excavate around 4.5 feet. Put soil barrier, 6″ packed stone with internal French drain placed for under slab area for water management. Pour the footer and the walls. Place the external French drain. Insulate the outside wall (comfortboard?) with drip screen covering. Inside place 3″ xps foam, vapor barrier, thermal bridge (is comfortboard ok here), rebar and radiant pipes, pour the slab. Is this the correct layout of everything and appropriate insulation to use. In this case, it would seem that the basement walls would then need to account for the 3″ of foam. The foam wouldn’t be deeper than the footer?

Old thread recommended against comfortboard again the concrete. Is that still the case and if there is external. Does the 15% external rule apply sub grade?

appreciate the insight.