In reply to Brian Fahs.

Yeah, that monstrosity is the evangelical church. Wow, and their music is even worse than their building, and they play it LOUD and PROUD at all sorts of inhuman hours.

I don't know that there is a stipulated minimum slab thickness in the IBC, but there are a lot of performance criteria that make a 4" slab pretty impractical. Floor live load deflection can't exceed L/360, and residential floors have to support 40psf live load as well as a 2,000 pound concentrated. Also, with 4" of concrete, the big problem is what you mentioned already: how do you fit any M/E/P inside and still have any concrete left to do the work?

Another bad thing I didn't mention is that the slab shown is going to act as a roof until they get around to expanding to the second floor, a few decades from now. They don't put any sort of waterproof membrane up there, so the water that pools eventually makes its way into the microfissures and they have all sorts of moisture problems in these houses. But I guess if you cook over an open fire inside, the smoke will get you before the mold does. :?