best way to insulate 3rd floor

[farmerpsv]

hey all,
have a 3rd floor living space that i want to insulate...floor is already done. knee walls are 5', the cathedral ceiling is 4' 6'' on each side and the ceiling is 9' 6" across. room is 38' long. was thinking of using the reflective bubble insualation between all the joists along with fiberglass. also thought of using poly board with a reflective surface. lots of different ways. some put the reflective barrier against the plywood others on the rafter. any thoughts? anyone have a third floor they had good success with? third floors are notoriously hard to cool, so i want to do this right.
thanks
paul

 

[SPIKER]

one thing you need to do is put the styro-foam stand offs in between the joists so the roof can still cool/breath

ok anyhow got to fly.

mark m