How would you do a Slab on Grade with a post and beam garage in New Hampshire?
...for a slab on grade, we prefer to to stay on grade and install a skirt of insulation around the perimeter of the building.
One inch of EPS foam insulation insulates comparatively to 1 foot of dirt, so laying a 4 inch skirt is much more simple than digging a four foot trench. You can see here in the images on this page ...