Replace attic insulation or just add

[Elizabeth J Humphrey]

Home built 1980, original installation. Wondering whether to blow in insulation on top of old or take out old before putting in new insulation.

[Account Closed]

Unless there is a problem with the existing insulation, typically just adding to it is fine, although be sure that there isn't a barrier (e.g., plastic, paper, foil, etc.) of any kind between the old and the new and that if your area/code requires ventilation of the attic, that the new insulation doesn't interfere with such.