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While not every wall requires a vapor barrier, if you do need one and don’t install it, moisture can get between the walls of your home. This can lead to water damage from mold growth or rot, and the excess moisture could also attract pests, including termites, cockroaches, or ants.

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.

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.

It is possible to install a radiant barrier yourself. However, knowing how to install a radiant barrier and actually doing it are two totally different things. For example, it’s important that they be installed in a straight line but at an angle that creates a gap between the roof panels and the foil or spray. If this gap is too large or small, it won’t function as it should, and that may be hard to avoid if you’re only a novice. When in doubt, leave this job to a pro.