On the Contractor side:
From the get go, plan to use IC on any top floor, or unit seperation. (Condos or Apartments that might become condo's, odds are some has some secret plan to do just that.) Irreguardless of insulation or not. (If there's not any now, there will be!)
On of my first questions walking a job is "Is there any insulation, and where? Is there any plan to have insulation anywhere else? Are you sure?"
Some places will accept Non-IC boxed out from insulation, to eliminate contact with the insulation. 3-6" But its a call to your inspector...
Fire rating is diffrent ball of wax... But wise to note as well in the same topic.
