Hello just purchased a house which used to have a flat roof but was converted to pitched, and as a consequence has 6 inches of fibreglass lying on what used to be the old concrete roof. I really want to board this out and ideally remove the fibreglass. As I have no joists, can I remove all the fibreglass and use either kingspan (then board on top of) or that silver thin material that is super insulating and board on top of that ? Many thanks