insulated roof

I'll preface this by saying that the builders the PO had in doing this extension were complete clowns and there are all sorts of idiotic things we keep finding around the place (example: laying an entire floor and then treading paint all over it and not bothering to clean it up), but this one...

I'm looking to convert our loft in our grade II listed property. My main concerns are around maintaining ventilation and finding an insulation solution. The loft floor has already been boarded up using loft boards, and they have used 100 mm of wool insulation beneath. There is not enough head...