Warm roof insulation advice please.

[BREAKALEG]

We are preparing and decking out a flat roof this week and could do with a little advice, were thinking of a warm deck made up of firing strips, 18mm ply, 110mm celotex, 18mm ply and 3 layer of torched on felt the reasoning for the lower level of ply was to ensure a good fixing when screwing the upper ply through the 110mm celotex.
I no you can get insulation board with 6mm ply bonded to one face but my roofer has said that it can de-bond and often the screw heads can grin through due to the flex.
Would the lower ply cause issues with the vapour barrier or condensation etc?

 

[dilly]

Hi i always do it this way again firrings then shuttering ply then visqueen membrane then kingspan tr26 at 85mm then the 18mm ply all screwed together with 150mm screws hope that helps.I dont know about the bonded insulation never used it all i can say about the above is its never failed

 

[BREAKALEG]

Thanks Dilly, spoke to celotex tech advice today and they backed up what you suggest.