I had a round or two with a GC over a job like this a year ago. Same type deal, no plans, design/build, lets play contractor and engineer. All I can tell you is stand your ground on this. This will fall under "places of assembly" where if you go the EPVC route, you'll have to stick to the fire rating requirements. But as long as you have a 15 minute barrier the EPVC will fly. I ended up going RMC and EMT and they paid a pretty penny for not getting the slab work done. All I can say is call the inspector and fill him in on the situation.
