crawfordrush

I'm designing a house that I want on a 6" or 8" slab (i'm using infloor heating). I want to use a 4" slab in the garage & shop area. The house has 6.25" (12" total ICF walls) and the garage/shop will have 4" ICF walls. The walls have been easy to change, but I'm having difficulty changing my slab thickness in the different areas. Does anyone know how I can achieve this please?