Insulated Parapet GRP (Fixing OSB through insulation into aerated block)

[MrTopOut]

Hi, as the topic title, I am looking to install a GRP warm roof onto an extension that has a parapet formed by the cavity wall extending, with 2 course of thermalites in the internal parapet face.

 

Has anyone had any experience of insulating a parapet with a GRP roof covering

 

My intention was to fix OSB directly to the aerated block that forms the parapet upstand, and sandwich 25mm PIR in between

 

I've done a small sample using a 75mm wood screw and it seems to hold extremely well, not sure if anyone else has any thought or advice