A composite concrete flooring can provide you with the 1.5 hour rating if done correctly (6.5" concrete on a 2" composite steel deck = 2 hrs.). Perhaps look at polyiso board to make up the desired R-30 value. typing out loud, maybe look at a raised floor system above the 1.5 hr rated flooring, then the underside can be exposed to the elements and your insulation is nested away in a tate access floor, my .02 cents, your call.

Insulated metal panel is a bit of misleading term. Yes, such panels incorporate insulation, but the role of the insulation is primarily as a board stiffener. R value of these panels is always ignored as thermal bridging between each panel is huge. Also, if the panels are used in a rainscreen principle assembly (as opposed to fully sealed), then effectiveness of such insulation drops down to zero. The link that you submitted shows a finishing solution worthy of disposable highway architecture.

I would strongly recommend NOT using a fully sealed panelised insulated metal system for any ceiling purposes. A dropped down ceiling (with separate insulation install, either board or sprayed on) is the cheapest, easiest way. "MetalWorks Vector for Exterior Applications" by Armstrong is a simple solution. Someone down the line will need to get access to the underside of the structure. You're just fucking with them from the past...

@Todd: Placing insulation on the inside of waterproofing and structure is always a bad idea. Floors especially: think of where dewpoint would occur in such assembly, and then think of where the moisture would end up being trapped.

At this point, I'm not sure about cost... but wouldn't it be easier (and perhaps even more long-term) to enclose the floor and add in mechanical ventilation?

I'm assuming there already has to be a fire system in place?

@Unicorn: Are you proposing the garage will be a heated/cooled space? I hope not. If not, you will still need insulation to separate the occupied spaces from the garage.

No, just merely suggesting that having a mostly sealed pocket of air (given enough of a shade over hang to said garage) could act by itself as an insulator.

Perhaps some motion/heat detection system that would only evacuate air out of the garage for running/hot/moving vehicles.

Until that crack in the ceiling slab poisons an entire family sleeping above. There's a good reason why garages are open air. Carbon monoxide is just too dangerous to dick around with. Also, you haven't considered that this project may be in a cold climate.

thanks for the suggestions so far guys.. its appreciated.

ok, it is an open air garage in a cold climate, we need to separate the cold in the garage from the warm above the slab, but we also need to keep the plumbing penetrating below the slab from freezing.

the ceiling space will most likely need to be ventilated with warm air in winter months because the insulated ceiling will not keep the pipes or the floor above warm if there is no heat in the space.

air leakage is a major concern
fire rating can be achieved at the slab
and i will have sprinkler piping in the ceiling space (i was thinking this might need to be a dry system because the sprinkler head penetrating the soffit will freeze otherwise.

thanks again for the help

also durability is a concern, (aesthetics are not inside this garage)

"the ceiling space will most likely need to be ventilated with warm air in winter months" uhhh why? You will need to insulate all the pipes separately from the ceiling itself. Heating a plenum space above a garage seems like an overkill.

Your biggest problem will be achieving R30 regardless of the system you chose. K13 (or John Mansville products) spray on insulation is the most common way of treating such conditions. These systems can achieve up to R20 and R 25, respectfully. There are some products that may achieve up to R30, but I'm too lazy to look them up right now.

Good luck!