My dormer room is an ice box. My plan is to install kingspan thermapitch tp10 between the rafters and also insulate between the joists with ecose. The plasterboard does not run with the rafters so in effect I have removed some plasterboard to gain access. I think these are known as crawl spaces to the rear of the room and either side of the dormer window. I have a trap door which gives me access to the area above ceiling. Will this insulation solve the problem or will I still have cold bridges behind the plasterboard. Should I insulate directly behind plasterboard as well where it is vertical? I also have some concerns about ventilation?