My 1930s house has a 3 foot tall undercroft which spans the space of the kitchen/diner. Roughly half of the houses flootprint. Our kitchen/diner is always a bit colder than the rest of the house and the (karndean) floor is colder which I suspect is due to the undercroft. We have an efficient and good sized radiator which ensures the room heats up but it takes longer than other rooms. What is the best way of insulating it? I am considering something like this https://www.screwfix.com/p/ybs-airtec-double-1-5-x-25m/50913 and stapling to the joists under the floor in the undercroft. My only thought is around ventilation. I'm assuming the undercroft helps with airflow to the house to stop damp/condensation? I intend to replace the undercroft door and looking into cavity wall insulation for the exterior wall. We also have a trifold door leading out but it's recently fitted so I doubt it's causing significant heat loss. Am I on the right track with this idea?