We've just moved into a big inefficient home on an island in marine zone 4 (PNW). Its currently heated with electric baseboards which seems the same as burning the required cash in the fireplace. We have an unconditioned crawlspace which will need to stay unconditioned for now (partially open and no perimeter drains). I've decided on under subfloor AL plated hydronic. The hard part seems to be determining how to insulate/vapor barrier the joists. Research has driven me to R24 Rockwool between the joists and R5 EPS (R10 later if needed) to keep the bottom of the joists from picking up too much moisture. I'll seal the EPS joints and insulate the sill plates to make it air tight. Where does the vapor barrier go though? None? Remember, this is an unconditioned space...

Not an expert but I would say at the floor level because in winter moisture is going to be flowing outward. Floor level is hard so is none the correct answer?