Radiant heat shop floor:

Top soil has been removed
very hard base ground (use a breaking bar to be able to dig in it)
3-7" of 3/4" crush gravel

moisture barrier HERE?

2" polystyryene extruded foam insulation

moisture barrier HERE?

concrete reinforcement mesh
1/2" pex heat tubing
4" concrete with plasticizers and fiber reinforcement

Everyone in the businss has a different opinion if it's below the foam
or on the foam.

Concrete engineer says on the foam
radiant installer says below the foam.

Alan