Whether you should replace 20-year-old insulation depends on its condition, type, and whether it meets current energy codes. Insulation installed around 2006 is typically fiberglass batts or blown-in fiberglass that is still functional if it has stayed dry and undisturbed. Fiberglass does not degrade chemically, so its R-value does not expire. However, after 20 years, several issues reduce performance. It may have settled, been compressed by storage boxes or workers walking in the attic, become damaged by roof leaks, or been disturbed by electricians and pest infestations creating gaps and voids. Attic insulation that was R19 in 2006 is now far below the current code requirement of R38 to R60 in most climate zones, so you are losing 20 to 30 percent more energy than a properly insulated home. If your insulation is thin with joists visible, uneven, stained by water, moldy, or has rodent droppings, you should remove damaged sections and add new insulation. In most cases, you do not need to remove all 20-year-old insulation if it is dry and in decent shape. You can air seal attic leaks with caulk and foam and then blow additional cellulose or fiberglass on top to reach R49. This topping up method is cheaper and effective. Replace it completely if it is vermiculite, has been soaked, or is contaminated with mold or animal waste.
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