I recently bought a 1980’s house which was very cold in winter and did not heat up, so on further investigation (lifting floors, cutting holes in walls) I have found that the builders used very little insulation when building it.
Here I am in my main bedroom which is on 1st floor, in a sloping roof part of the house. I cut a hole in the wall to see if the eaves we’re insulated and found that not only were they not insulated, but neither was the stairs and any hot air coming up from the ground floor would just disappear out of these spaces rather than stay in the house!!
Part 2 Here: https://www.youtube.com/watch?v=I4HKgAkXIms