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The life span of fiberglass insulation can be as long as 80 to 100 years, but because of changing building codes, it’s best to get your insulation checked every 10 to 15 years. Signs of degrading fiberglass insulation include bits of batts on the floor or batts detached from frames. Having optimal, healthy insulation in your home will improve its energy efficiency, lowering your monthly bills.

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.

Insulating windows without plastic is usually the better method. Outside of simply replacing your windows, you could buy cellular shades, which trap air between the window and the home, add a window film that blocks UV rays and traps heat, or cover your windows with a low-emissivity coating called “low-E.”

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.