Attic insulation loses effectiveness over time, though how fast and for what reason depends on the material. If your home’s insulation hasn’t been checked in ten or fifteen years, there’s a good chance it’s not performing at the level it was rated for when installed.
Fiberglass: Settling and Compression
Fiberglass batts and loose-fill don’t chemically break down, but they do settle and compress over years, especially loose-fill fiberglass, which can lose a meaningful percentage of its loft — and therefore its R-value — over a couple of decades. Foot traffic in the attic, stored items placed directly on insulation, and simple gravity all contribute. Fiberglass batts that have been walked on or crushed under ductwork also lose effectiveness in those specific spots even if the rest of the attic looks fine.
Cellulose: Settling Is Built Into the Math
Cellulose settles more noticeably than fiberglass — installers generally account for this by installing extra depth upfront, since a certain amount of settling is expected within the first year. Beyond that initial settling, cellulose holds its loft reasonably well as long as it stays dry. The real degradation risk for cellulose is moisture exposure: a compressed, water-damaged section of cellulose loses R-value and can develop mold, which is a bigger issue than gradual settling.
Spray Foam: The Most Stable, With One Exception
Properly installed and cured spray foam holds its R-value better over time than fiberglass or cellulose since it doesn’t settle or compress the same way. The exception is if it was installed at incorrect thickness, mixed improperly, or exposed to significant roof leaks — foam can degrade at the edges or delaminate from the surface it’s sprayed on if there’s ongoing moisture intrusion.
What Actually Causes Degradation
- Time and settling — gradual and mostly unavoidable, especially in the first year or two after installation
- Moisture exposure — roof leaks, condensation, or high humidity events like monsoon season can compress and damage any material
- Physical disturbance — foot traffic, stored boxes, pets, or pest activity crushing or displacing insulation
- Extreme heat cycling — the repeated summer heat and winter cooling in Las Vegas attics doesn’t damage most insulation directly, but it does stress the areas around ductwork and can accelerate settling near heat sources
- Pest activity — rodents nesting in insulation compress it and contaminate it, on top of whatever other damage they cause
How to Tell If Yours Has Degraded
The most reliable check is a visual depth inspection — insulation that’s visibly thinner than it should be for its R-value rating, or that’s noticeably compressed, patchy, or discolored, has lost performance. Rising cooling bills without any other explanation, uneven room temperatures, or ice-dam-style issues (less common here, but relevant for higher-elevation properties) are also signs worth investigating.
When to Top Off vs. Replace
Most attics don’t need a full replacement — topping off with additional blown-in material over existing, otherwise-healthy insulation is usually enough to bring coverage back up to current recommendations. Full replacement is really only necessary when the existing material is water-damaged, moldy, pest-contaminated, or when it’s an older material like vermiculite that needs to be professionally removed rather than built on top of.
If it’s been more than a decade since your attic was checked, or you’re noticing higher bills without an obvious cause, the team at Attic Insulation Las Vegas can measure your current depth and coverage and tell you honestly whether you need a top-off or nothing at all.
