Insulation, Radiant and Vapor Barriers - Insulating top floor of a corner lot row home

Questions:

I am about to install a new drywall ceiling at the top floor of a row home unit, but first i want to address the insulation issues. The current scheme consists of FG roll (R-13) laid out b/w and attached to the roof trusses. I don't know if this is appropriate for a flat roof system or not. It does not appear that the thickness of the roof would allow for a thicker sized insulation. The only thing i thought may work would be to lay out thicker insulation across the new drywall ceiling, as i put it up. Much like what you see above drop ceilings, w/ the insulation dirctly ontop of the drop tiles.

First, would this work.
Can or should i leave the orginal insulatioin in place for added value. Would this create an unsual plenum w/ insulation above and below it.
What would be a good RValue to use.

Any other ideas or suggestions?

thanks

Could you post more info? I'm not sure what B/W means. If you have a flat

roof, I doubt that you would have ''trusses''. If you don't have room for more

than R=13 insul., you would only have 2 by 4 rafters which would be very

unusual for a flat roof. Not trying to pick your posting apart, I just need more

info and clarrification. Putting insul. directly on a suspended ceiling panel is

not recommended.