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Rockwool insulation can last up to 100 years, but just how long this insulation lasts in your home depends on how well it's maintained. Poorly installed insulation may last only 30 years, so be sure to regularly inspect your home's insulation for water damage, settling, and pests to give your insulation the best chance of having a long lifespan.

Yes, usually you will need some kind of vapor barrier on the exterior walls when the framing is attached to concrete and masonry surfaces.

A plastic vapor barrier should completely cover your basement to prevent water from penetrating through the walls. This typically goes before installing insulation to prevent moisture from building up and becoming trapped on the inside of your insulation, where it can collect and lead to mold damage. Installing insulation after the vapor barrier allows for any moisture to exit the walls for better ventilation.

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.