Following on from my previous thread I'm planning to start IWI installation on my victorian renovation in a couple of weeks time. My proposed  buildup: Existing Solid 9" brick external wall 60mm foil backed PIR (Will serve as VCL) 35mm timber battens/service cavity. (Fixed to brickwork with concrete screws) 12.5mm plasterboard  Gypsum skim coat     I'm generally confident this arrangement will perform in my particular situation, however there