Attic insulation, especially fiberglass, should be replaced every 15-20 years, particularly if it has been exposed to moisture or mold.
For stapling insulation, 20-gauge staples are recommended, though 19-gauge and 23-gauge staples can also be used.
Mold on insulation often appears as black, brown, or greenish discoloration and is accompanied by a musty, dank odor.