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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.

While there are many different kinds of insulation, spray foam, blown-in, foam board, and batt and roll are the four types you’re most likely to see. That doesn’t mean they’re alike, though. Each one varies drastically in terms of cost, materials used, and how they’re installed—not to mention, how well they limit heat transfer.

Mineral wool wraps are the most affordable and effective insulation for crawl space ducts. They are easy to cut, last for a long time, and healthier for humans. Meanwhile, fiberglass wraps are cheaper but more hazardous and difficult to handle. If you do choose to use a fiberglass wrap, make sure you are wearing long sleeves and wear proper protective gear.