Normally, no. You do not need to remove your old attic insulation before installing new insulation. But, in certain circumstances you should. If you've had a pest infestation such as rodents, mice, squirrels... it is highly likely your attic insulation has food, urine and feces - so yes, you definitely want the old insulation removed. Another reason to remove old attic insulation is to improve air quality by removing dust and other harmful materials that might affect your living space. We recommend following this rule of thumb: It is perfectly fine to add new attic insulation over the top of old except when the old is likely to have a negative effect on your health and / or indoor air quality