All buildings need a structurly sound supporting base. And that has to sit on ground that won't freeze and can support the building.

But there are wildly different weather conditions, soild types and conditions, building loads, building practices, etc.

So the footing might just a footing that is 4ft in the ground with a frost wall and separate slab. It might just be a 24" thickened edge on slab. Or it might be an extension set of piers with grade beams that support the slab.