New build with room in roof trusses. I am confused as to what meets regs. Can I have insulation boards just between the trusses (eg Celotex or Kingspan) with plasterboard over or do I have to also have some over this, intruding into the habitable space thus reducing the room sizes up there. I have emailed the building inspector and I can't make head nor tail of his reply. If I want to use foiled boards, what size please? Can I use an 'on a roll' type or batts? Just want to know what's acceptable as I probably can't afford to insulate it all in one go and will have to buy it in dribs and drabs as I go along. If I know my choices I know what to look out for basically. Thanks in advance.