The building is one level on a floating or bell slab. We did not insulate under the slab, since we felt that this would cut us off from this natural heating and cooling. Instead we used 2 inch rigid foam insulation on the vertical sides of the foundation slab, than we used 4 foot by 8 foot sheets of rigid foam, butting them up tightly length wise to the bottom of the foundation at a downward pitch for drainage.
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