I am confused on how to insulate an elevated floor where the room above will be conditioned space. Live in zone 2. Have 2×10 floor joist. I read where code states minimum R13. 

Would like to achieve R19 or a little higher. Since 2×10’s are 9.25” and R19 is only 6.25”, would there be a problem leaving the 3” gap below the fiberglass? I am planning on attaching foam board and/or osb on bottom of joists to help with protecting insulation. Any vapor barrier required?