How long does insulation last?
InterNACHI's baseline chart gives fiberglass, cellulose and foam insulation 100+ years apiece, and the makers' own trade body says the same in stronger words: NAIMA's summary of the research is that fiberglass and mineral wool "do not experience a reduction in thermal performance over time, nor is settling an issue". There is no warranty bar on this page, and the reason for that absence is the honest part.
Updated
Typical service life: 100+ years
Every insulation line on the chart reads the same — batts and rolls, loose fill, fiberglass, cellulose, rockwool and foam board are all "100+" — and the chart's own note attaches the condition: as long as they are not punctured, cut or burned and are kept dry and away from UV rays, these materials will last a lifetime. NAIMA, the fiberglass and mineral wool manufacturers' association, publishes the research behind that claim on its Insulation Institute site, including a study in which eight fiberglass batts between 30 and 40 years old still performed at 95.5 percent of their labeled R-value. The figure describes material lying undisturbed. It does not describe the insulation actually in your attic, which has been walked on, wired through, pushed aside and stored on.
Tier 3 · baseline chart (undated) Range from InterNACHI — Standard Estimated Life Expectancy Chart for Homes, checked 2026-08-27.
Climate does not shorten insulation so much as decide what goes wrong with it. In a cold climate the failure is moisture from inside the house condensing in the assembly on its way out; in a hot humid one it is the reverse, outdoor air condensing on the cool side of the same wall. Either way the material itself is fine and the water is the problem — which is exactly why every published life figure for insulation arrives with "kept dry" attached to it.
By material
| Material | Typical service life | Source |
|---|---|---|
| Fiberglass batt | 100+ yrs | Tier 3 · baseline chart (undated) InterNACHI |
| Blown cellulose | 100+ yrs | Tier 3 · baseline chart (2007) NAHB (National Association of Home Builders) |
| Spray foam and foam board | 100+ yrs | Tier 3 · baseline chart (undated) InterNACHI |
Why there is no warranty bar here
Insulation is sold by the bag and the batt against a printed R-value, not against a term of years. Some fiberglass makers do advertise a limited lifetime warranty on the material, but on the day this page was checked none of those documents could be opened and read at a public address — so no bar is drawn here rather than a term quoted from a marketing line nobody can check. What an owner actually holds is the label and the certificate: the R-value and coverage marked on the package, and the installation certificate an insulation contractor leaves behind stating the thickness, coverage and R-value actually installed in the attic. That certificate is the enforceable paper in this part of the house.
What shortens it
- Water: a roof leak, a bath fan ducted into the attic instead of outside, a wet crawl space — wet insulation stops working long before it stops existing
- Anything that takes away depth, because depth is what the R-value is: loose fill that has settled, batts crushed under storage, foam that has pulled back from the framing it was sprayed against
- Being walked on and pushed aside, which is what happens to attic batts during every wiring, cable and duct job the house ever has
- Compression: batts stuffed into a cavity too shallow for them, or blown material packed hard behind a stud bay, both lose the loft they were rated at
- Plywood decking and storage boxes laid straight onto attic insulation, which flattens it under everything you put up there
- Rodents and birds nesting in loose fill and tunnelling through batts
- Sun and weather wherever insulation is left exposed — the chart's own condition is that it stays dry and out of UV
Signs of wear to look for
- Blown attic insulation sitting visibly below the depth markers stapled across the joists
- Batts sagging away from the top of a wall cavity, or hanging out of a basement ceiling
- Dark, sooty-looking staining on the face of a batt, which marks air moving through the material rather than around it
- Gaps opened between spray foam and the framing it was sprayed against, or foam pulled back at a rim joist
- Insulation matted, discolored or crusted under a roof leak, a bath fan, or a plumbing wall
- Rooms over the garage, or beside the attic hatch, that run cold in winter and hot in summer while the rest of the house is comfortable
Older wiring buried under attic insulation, and insulation that has been wet long enough to stain and mat, are not things to settle from the hatch with a flashlight — that is an inspection question, not a web-page question.