Celotex XR4150 for warm roofs and bonding of VCP polythene

[Luca]

Hi there, 

 

https://www.insulationsuperstore.co.uk/product/celotex-xr4150-zero-odp-rigid-insulation-board-150mm-x-1200mm-x-2400mm.html

mentions this type of celotex for cold roof - is it suitable as a warm roof insulation layer as well. Where should the foil side be and what fixing should be used.

 

Also, if using a polythene sheet like this as Vapor control barrier, how should it be bonded to the OSB - are nails ok?

 

https://www.beatsons.co.uk/building-supplies-c2514/builders-metalwork-c2632/polythene-c2640/beatsons-green-vapour-barrier-125mu-4x50m-p27247

 

Many thanks!