I am currently building an extension and according to my drawings I need 100mm Kingspan between rafters and then 62.5 mm insulated plaster board. It’s not really clear but I guess I fill between the rafters up to the ceiling joists and then fill between joists then insulated plasterboard all over.
my question is could I just place 150 mm PIR between the joists and then stick to the original plan of 100 mm and 62.5 mm over the rafters that form the ceiling ?
my question is could I just place 150 mm PIR between the joists and then stick to the original plan of 100 mm and 62.5 mm over the rafters that form the ceiling ?