Will be building a 12' x 12' room inside our shop building as temporary living quarters while we construct our ICF home.    The existing 5" thick concrete shop floor is not insulated underneath.  We did run plumbing and drain lines for a toilet/shower/sink.  Had thought we would just frame a raised floor with 2x4s on edge with a vapor barrier, 2" pink board and decking.   

Another option we are considering now is to place a vapor barrier with 2" pink board, then run a loop of radiant PEX and then place 1.5" of lite weight concrete or slurry.  We'll address the radiant heat source later, but want to have the capability.   This would give us a contiguous insulated floor area.

Is 1.5" of concrete thick enough over the foam?  Any other recommendations?  Dave