While IECC 2021 allows for commercial buildings in cold climate zones to insulate just the perimeter of unheated ground slabs, the net zero and passive house commercial buildings I've seen in colder climates have had continuous ground slab insulation, for the full slab.

Has anyone seen a study conducted for commercial buildings that made the case for exceeding code?

If not, and we need to do our own study, which tools are better than others at capturing losses at the ground slab?

Thanks!