Insulating concrete stem walls and slabs?

[karl81435]

I am about to build in a cold climate and I will have a basement with concrete stemwalls and slab as well as a garage with concrete stem walls and a slab at grade. I will be using traditional pre made forms. What walls and/or slabs would I want to insulate on the exterior?

The basement may be used for living space. The heating system is forced air, not in floor heating.

I was planning to waterproof the stem walls and insulate them with rigid insulation on the exterior, but not the slabs. My logic is that the basement slab is well below the frost depth and there will be some heat available from the ground, 50 degrees possibly. The garage slab is at grade, but I do not care if that slab is cold. I have been advised both ways, but most of the advice I received is based upon tradition instead of reason. What would you recommend I insulate?

Thank you,
Karl81435

[Rich]

My recommendation would be to insulate all foundation walls only. As you stated there is really no reason to insulate the slabs unless there is a specific reason for it. Typically a radiant heat supplier will recommend to insulate the slab because of heats natural tendency to travel from hot to cold which pushes the heat into the room and not into the ground.