I am building a home in zone 5, Northern NJ. I am exploring the option of a creating a steel/concrete slab to encompass the entire first floor. 9′ sub-grade foundation walls (likely ICF) would support steel floor joists/beams, upon which Q-deck followed by rebar and poured concrete would complete the main floor slab. (structural engineer is looking at it, I priced the Hambro D-500 system, more than I liked, will compare to Q-deck/rebar/concrete) I am thinking of embedding radiant heat tubing in the structure, that would allow me to create a thermal slab of considerable mass. My questions, 1. Does this sound like a good idea? It would be more expense, but I really like the feel of concrete underfoot, plus its a fire/insect resistant base. Builder is a good friend of mine, has done it before, I’ve seen his last project, impressive. He feels is not that much more in cost. 2. With embedded radiant tubing, would it be better to lay down tubing in the slab to create this 4″ thermal slab, or install something like an EPS insulated floor panel system on top of the slab that holds the tubing and you mud-floor it in place with sand/cement or gypcrete. Thus isolating the warmth of the slab to the superficial 1.5″ or so? I imagine it would require more energy to heat the entire 4″ slab rather than just the superficial 1.5-2″. Heating the entire slab essentially creates a basement with a warm ceiling that will be under the sheetrock or drop ceiling anyway. Would the thermal mass provide a benefit beyond minimizing temperature swings? Thanks in advance for constructive input/comments.