Some loose insulation material (rockwool?) currently exists between the joists to a depth of approx 4 inches, though some areas have no insulation at all.As I only bought the house this year I have no idea how old the insulation is.
Am I better off to remove the existing insulation, which would be a rather messy and dirty job, and start from scratch or should I lay new insulation on top of the old stuff.
What's the best insulation to use and to what depth. I'd prefer to over-insulate than under-insulate. It is a lathe and plaster ceiling and part of the roof has floorboards. Any advice gratefully received.