Does slab on grade need to have in floor heating?

 A polished concrete slab on grade, or any basement concrete floor, will feel cooler to the touch than wood or other flooring materials, due to the conductivity of concrete. This is a simple fact of physics. Enough sub-slab insulation can be added so that it is possible to feel comfortable, but a wood floor or other flooring materials on top of concrete would definetely feel warmer. You can learn more here about the ways in which your personal comfort is affected in your home whether you realize it or not – 

How to Design a Home for Thermal Comfort 

You will often see Passive House projects that don’t put radiant heat in slab floors, but they always include extreme amounts of insulation in order to do so, in the magnitude of 10 -12 + inches of foam. Personally, I would not do a slab floor without heating it, I don’t enjoy cold feet. So if you are, it might be worth considering putting some pex tubing in the floor anyway (that would be perhaps a couple of hundred dollars depending on the size of the floor), so you were ‘radiant ready’ at least in case you found it to be too cold.  As for putting wood or other materials on top, that isn’t a problem, as long as you have vapour protection underneath, and let it dry before you do that. So in the case with radiant heat,  you can speed cure it by running the heater and then do a moisture test. That is as simple as taping down a sheet of poly to the slab some place, give it a day or two and see if any moisture droplets form under the poly, then you know its dry, at which point it should be safe to put wood on and it not get moldy. If you don’t heat the floor it would take longer dry completely just heated ambiently from a wood stove.  And as for deciding between a slab on grade and a crawlspace, have a read here for some things worth considering - 

Slab on Grade or Crawlspace - Which is Better? 

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