Mark Mandell - Gone Round In New Jersey
The Dreaded Codeman cometh.

You son is correct, you've got work to do. Footings will have to go below the frost line (here 3') and the slab must be supported. Stabil on fill will not get you (or your heirs) a CofO.

My group did one of these "conversions" for a member and when we got done with the planning stage and township approvals, it was cheaper to bust up the existing porch/slab and start over, footers to roof, from scratch. We wasted a whole bunch of time trying to get 'round code requirements. We wound up doing a slab-on-grade mono-pour for a 24x24 addition, complete with hot tub.