New insulation can be placed over the top of existing insulation without much complication in most circumstances. You should first carefully inspect the existing insulation to ensure it isn’t damp or otherwise compromised. Hiding damaged insulation behind new insulation will end up costing you more in the long run than removing it and going with all-new insulation. If your existing insulation looks good, know that you don’t need as much as you would when going all-new (see the next question for more details).