Insulating a flat roof

[cjb1971]

Refurbishing the kitchen which has a flat roof, ply covered by felt,what is the best way to insulate from the inside?
First thought was insulation roll but the bits i put around the edge have caused damp where in contact with the ply, so i guess that idea is a non starter.
Now thinking cellotex between rafters leavingan airgap above?
Long term will replace roof and put warm deck insulation on the top.
Short term best way to insulate??

 

[Alastairreid]

Full fill with rigid insulation hard against the underside of the decking.
vapour barrier fitted across the joists and taped.
foil backed plasterboard as a belts and braces approach.
The idea is to prevent moisture reaching the underside of the deck

No point leaving an air gap unless you have vents at fascia and abutment.

 

[noseall]

Wot he says.^^

 

[cjb1971]

Due to yhe electric cables and pipe work going through the roof void fitted 50mm cellotex (100mm joists)
Cross ventilation fitted into the air gap.
25mm cellotex fixed onto joists before plasterboarding, all cables running through the void and pipes in the insulation,hell of a lot warmer now