Hi James,
Yes, we will have a frost-protected shallow slab foundation under the existing garage door openings since there is no foundation there. The residential code prescribes the size, depth, and insulation requirements for the thickened slab edge. In our location, we need a 12″ deep thickened slab edge along this opening and then it can taper back to the standard 4-5″ thickness everywhere else. The entire edge and underside of the slab will be wrapped in R-5 insulation board. All of this is something our concrete sub can easily do when he pours the slab so its a much more cost-effective solution to a traditional footing and foundation wall (which would have required more excavation, more materials, and a few thousand dollars more). Thanks for the comment, Cheers!