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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.

Each of the three types of wool insulation has particular disadvantages. While their R-value is higher, they all cost more than fiberglass versions. Installing mineral wool and sheep wool requires protective gear. Because of its vulnerability to insects, chemicals are used in its production. Hemp wool is more costly to install than other types because additional tools and labor are involved.

It is usually possible to install insulation yourself, but it’s often better to hire an insulation professional. An experienced insulation pro can determine which type of insulation is best for your space and the R-value get the most value and comfort in your home. Certain types of insulation can cause skin, eye, and lung irritation, and a professional will have the equipment necessary to keep themselves safe and limit the effect on your indoor air quality after the installation. Certain types of insulation—like blown-in and loose-fill insulation—demand a professional for proper functionality and safe installation.

Mineral wool has an excellent life expectancy of up to 50 years, provided it's kept dry and free of pests. Compared to fiberglass, with a life span of 20 to 30 years, mineral wool stacks up well for long-term cost savings. Sheep wool maintains a similar life span to fiberglass, while estimates for hemp wool insulation life expectancies are all over the board, ranging anywhere from 20 to 100 years.