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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.

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.

Insulating your home's exterior walls can realize up to a 20% reduction in your monthly energy bills. This means that regardless of how much the project costs, it can begin to pay you back immediately. Additionally, adding spray foam and other high-end materials can increase the selling value of the property.

The most affordable way to insulate behind unfinished walls is to install fiberglass batts or rolls. These total around $0.75 per linear foot, with the width matching the gaps between standard studs perfectly. However, it’s important to consider the R-value of your insulation and the climate in your area, as fiberglass insulation isn’t the best in terms of preventing heat transfer. Plus, the most affordable option may cost more on electricity bills over time. The most affordable way to insulate behind finished walls is to leave them up and use blown-in insulation to avoid drywall replacement.