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Ideally, you can add new insulation to your existing insulation. However, some circumstances require you to remove old insulation before adding any new insulation: 

• If the insulation is over 15 years old

• If the insulation is wet or moldy

• If it is vermiculite insulation

• If you see signs of pest infestation

Removing old insulation is best left to a pro who can safely dispose of potential moldy or asbestos-ridden insulation.

While insulation is required for all exterior walls in a house, it is not typically required for interior walls. Local and state building codes mandate that new construction homes have adequate insulation in exterior walls and ceilings to suit the local climate.

However, there are several benefits to adding insulation to interior walls. It is excellent for sound-dampening between rooms and can help with temperature control by maintaining a regulated temperature in specific rooms and lowering heat transfer between adjacent areas. Insulating interior walls can also contribute to the overall energy efficiency of your home.

A plastic vapor barrier should completely cover your basement to prevent water from penetrating through the walls. This typically goes before installing insulation to prevent moisture from building up and becoming trapped on the inside of your insulation, where it can collect and lead to mold damage. Installing insulation after the vapor barrier allows for any moisture to exit the walls for better ventilation.

You do not always need to remove old insulation before adding new. If the existing insulation is in good condition—not wet, physically damaged, moldy, or infested with pests—you can add new insulation directly on top of it for a compounding effect. You can also mix different types, such as adding blown-in insulation around existing fiberglass batts.

However, removal is recommended if the old insulation is compromised by water damage or pests. You should also remove it if you plan to install a different type of insulation, like switching from roll or batt insulation to spray foam. If the existing insulation is very old or damaged, you will likely get more benefit from removing it and starting fresh.