Concrete Slab on fill and radiant heat
WIRSOB Radiant Floors hePEX plus Cross-linked polyethylene
tubing with an oxygen diffusion barrier for closed loop hydronic radiant floor heating
systems. http://www.wirsbo.com/main.php?pm=1&mm=1&sm=1&pc=homeowner/ho_mm1sm1.php
What goes under the floor:
Layers:
Excavation of house footprint to ledge.
Install drainage system at low point.
Build concrete footings on ledge to level and start Insulated Concrete Forms (ICF) units.
Back fill to footing level.
Install ICF to window sills and underside of rafter at one location.
Install plumbing sewer drainage and test.
Build form work for sunken tub and shower
pan.
Back fill with granular fill to crushed stone level
Install Radon vent risers and piping grid. 
Back fill with crushed stone to cover Radon
piping. 
Install 2 inch insulation. 
Install vapor retarder. 
Install steel on 2 inch saddles #4 bars@ 12 inches on center both ways.
WIRSBO Radiant Floors hePEX plus Cross-linked polyethylene tubing with an oxygen diffusion barrier for closed loop hydronic radiant floor heating systems.
Install Wirsbo tubing.
Install under slab hot and cold water piping and test.
Place concrete floor and finish.