I have an outbuilding that I need to partition a section off and insulate so it can be used as an office. It is concrete base, brick walls and corrugated cement fibre board roof which is fixed to the purlins. The roof is in good order so I want insulate and board under it, build the partition wall and insulate the floor. I am uncertain of the best way to insulate the roof, I don't want to remove the roof but am concerned that insulating directly under it may create a condensation and damp issue. What is the best way to do this, also I am not keen on spray insulation.