I have a 1930’s close boarded roof, the previous owner insulated the roof space with polystyrene chips! (Total Fire nightmare and also difficult to remove). What would be the best way to insulate? I’ve looked at fitting 50mm celotex to the underside of the rafters with a 50mm air gap then covering with a membrane. Or should I just fit insulation across the ceiling joists? I have high ceiling joists so this obviously can cause issues with stopping airflow. Thoughts please.