How long does attic insulation last?
Updated August 2026
Attic insulation lasts 20–30+ years, but that figure hides a wide spread by material. Loose-fill fiberglass and blown cellulose settle 2–4 inches over their life and quietly shed R-value as they compact, so a blanket rated R-38 the day it went in can drift toward R-30 after two decades. Spray foam is the outlier, holding its seal for 80+ years because it bonds to the framing instead of settling. What actually ends most insulation early is moisture: a roof leak or poor attic ventilation mats it down, and wet insulation insulates almost nothing until it dries and is re-fluffed or torn out.
Lifespan by type and situation
| Type or situation | Typical lifespan | Why |
|---|---|---|
| Blown fiberglass | 20–30 years | Settles and loses loft; keeps insulating but at a lower R-value |
| Blown cellulose | 20–30 years | Settles 10–20% over time and is the most moisture-sensitive type |
| Fiberglass batts | 20–30 years | Long-lived if kept dry and never crushed by storage or foot traffic |
| Open or closed-cell spray foam | 80+ years | Bonds to the framing and does not settle; effectively lifetime |
| Mineral wool | 30–50 years | Resists moisture and fire better than fiberglass or cellulose |
| Any type, chronically damp | Under 10 years | A roof leak or missing vapor control cuts life to a fraction |
Signs yours is near the end
- Heating and cooling bills creeping up year over year with no change in your thermostat habits
- Rooms directly under the attic that run cold in winter and hot in summer no matter the setting
- Insulation visibly flattened, thinner than the ceiling joists, or matted down in patches
- Ice dams forming along the eaves in winter, a sign heat is escaping into the attic
- A musty smell or dark, water-stained insulation, which means moisture has gotten in
- Uneven coverage with bare gaps you can see the drywall or joists through
How to add years
Insulation does not need much, but the little it needs is decisive. Inspecting the attic once a year, and after any big storm, catches roof leaks and matted spots before they spread; fiberglass that dries out and gets re-fluffed can return to near-full R-value, while insulation left soaked has to come out. Keep the attic ventilated and air-sealed so warm indoor air stays out of it, which prevents the winter condensation behind a frosty or wet attic and the summer heat load behind an attic that bakes. Topping up thin blown insulation costs a fraction of a full replacement, and skimping on depth shows up on every energy bill. The U.S. Department of Energy recommends R-38 to R-60 for attics across most of the country.
What it costs to replace: plan on $1,500–3,500 to re-insulate ($1.50–3.50 per sq ft blown-in). Replacing on your own schedule, before it fails, is almost always cheaper than the emergency version. The home maintenance cost calculator helps you set the money aside before it comes due.
OnOtto tracks your insulation checks age and service history, and warns you before end of life instead of after the flood.
Track your home's systems, free for 30 daysFrequently asked questions
Does attic insulation really wear out, or does it last forever?
It does not rot like wood, but it degrades. Blown fiberglass and cellulose settle and compress over 20–30 years, losing loft and R-value even in a dry attic, so a 25-year-old layer may perform like insulation two grades thinner. Add any moisture, from a roof leak or poor ventilation, and it can be functionally dead in under 10 years. Spray foam is the exception at 80+ years. Most homes never rip insulation out; they top up the depth every few decades.
Can you just add new insulation on top of old?
Usually yes, and it is the cheapest fix. If the existing layer is dry and in decent shape, you can blow or lay new material directly over it to build the depth back to R-38 or higher. The rule is that the old insulation must be dry and uncompressed; adding fresh material over a wet or moldy layer just seals the problem in. Never lay a faced batt, one with a paper or foil vapor barrier, on top of existing insulation, because the trapped barrier can cause condensation.
How much attic insulation should I have?
The U.S. Department of Energy recommends R-38 to R-60 for attics across most of the country, which works out to roughly 13 to 20 inches of blown fiberglass or cellulose. Older homes often sit at R-19 or less, about half of what current guidance calls for. If you can see the tops of the ceiling joists, you are almost certainly under-insulated. Bringing a shallow attic up to R-49 is one of the higher-return upgrades a house can get.
Will more attic insulation lower my energy bills?
Yes, and the effect is measurable. Attic insulation is the biggest single barrier between conditioned air and the outdoors, so a shallow or matted layer leaks money in both seasons. Going from R-19 to R-49 in a cold climate can trim heating and cooling costs noticeably, with many homeowners seeing the upgrade pay back in a handful of years. Pairing insulation with air-sealing the attic floor multiplies the savings, since insulation slows heat while sealing stops the drafts.