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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.

Air duct insulation typically lasts for 10 to 15 years or even longer, depending on the material and maintenance. It's important to conduct periodic inspections to check for signs of deterioration, such as water damage, tears, or general wear. If you find any of these issues, it may be time for repairs or a full replacement. You might also consider upgrading your insulation even if it's in good shape to improve your home's energy efficiency and enhance your HVAC system's performance with newer, more effective materials.

In some areas, insulation companies require a special license, while some states only require them to hold general contractor licenses. Some municipalities may not mandate any license, although you should always ensure a contractor is fully insured. You can use Angi’s license lookup tool to confirm whether or not an insulation contractor you’re considering holds the necessary license for your area. You can also contact the company for information regarding licenses, certifications, and insurance.

The life span of insulation is between 20 and 100 years. At that time, existing insulation can fall victim to gravity, resulting in compression, which reduces its insulating protection or R-value. If you can't simply add more insulation over the existing material, removing the old to increase the effectiveness of the new can reduce your energy bills and make the project worth the time and money investment.