How long does insulation last?

Blown-in cellulose: 20–30 years (settles 10–15% over time; may need top-up around year 25). Fiberglass batt: 25–50 years (degrades from moisture exposure, not from age). Closed-cell spray foam: 50+ years (essentially the home's lifetime). Open-cell spray foam: 50+ years but degrades on water exposure. Rigid foam board: 50+ years. Insulation almost never fails by 'aging out' — the failure modes are water intrusion (roof leak, ice dam), rodent infestation (squirrels and mice tunnel through fiberglass + cellulose), and compaction (foot traffic on attic insulation). Inspect after any storm-water event or roof repair.