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What is the useful life of insulation, and why?

vapQZJtpem | Posted in Energy Efficiency and Durability on

In energy auditing, the useful life of blown in insulation (both fiberglass and celulose) is typically estimated to be 15 years. (in my experience) I would like some input on why that might be. My common sense is telling me it should be much longer. I read everywhere that cellulose, unlike fiberglass, breaks down over its useful life, but nowhere can i find where it specifies what the useful life is, or why.


  1. GBA Editor
    Martin Holladay | | #1

    "In energy auditing, the useful life of blown-in insulation (both fiberglass and cellulose) is typically estimated to be 15 years."

    Say what? I've never heard that. Specifics, please! What's your source? Rumors? An energy modeling program? A textbook?

    For three years I had my own company, providing capital needs assessments to owners of multi-family projects in Vermont and New Hampshire. I did a lot of research and compiled a lot of data on the useful life of a great many building components. I never saw any document that estimated that the useful life of insulation was only 15 years.

    Plenty of attics have 50-year-old insulation. In many cases, the only thing wrong with the insulation is the fact that it is thin and has a low R-value. But that's the way it was originally installed.

    In other cases, the insulation is a mess -- disturbed, damp, or contaminated with rodent feces. But I don't buy your 15 year estimate.

  2. vapQZJtpem | | #2

    Thank you Martin,

    I should have written that a bit differently. As i have been reviewing many energy audits as part of my job, I have found a range of useful life estimates for blown in insulation. I probably should jave just left it at that. I do not want to mislead anybody. What I am trying to find out is what thier source or justification might be. 15 years seems to be a fairly common value used. Actually, as I have looked back over a bunch of these, I think 20 years is probably more typical. I have seen at least one estimate of 30 years, and beleive it or not, one of 10. I have been building for 20 years. Like you, I would imagine that the estimated life of insulation should be more like 50 years+. Ultimitely, I just need to know how this is established for insluation. It is easy for something like a water heater, but not so easy here.

  3. GBA Editor
    Martin Holladay | | #3

    A couple of observations:

    1. Fiberglass batts do not age well. In crawl space ceilings, their lifespan is very short, and they often fall down and get water-logged and moldy. In stud walls, they are often contaminated with rodent feces, and in attics they are often stained from air leaks.

    2. Cellulose insulation should last indefinitely, in my opinion. If cellulose insulation ever has to be removed, it's not because of the age of the insulation, but because of some other failure not directly related to the insulation -- for example, a roof leak or rodent infestation.

  4. 5C8rvfuWev | | #4


    I'm not a building scientist of any stripe, but I'm not even sure of how you could test/measure that for a product in isolation, in any case. If the material is in a sealed space, I can't see why its life wouldn't be indefinite. If it is in an entirely exposed space, it would be immediately vulnerable. In practice, as Martin's post 3 suggests, it just "depends."

    I'm thinking of pine as cladding which has a reputation for a short life, yet on the Cape and south shore of MA where it is exposed to ocean air and well-ventilated, there are buildings where it has not received a protective coating yet is over 200 years old.

  5. BryanPringle | | #5

    Adding to this old conversation because of a rash of bad information I have seen lately. Insulation does not degrade of its own accord, and must be damaged by external factors.
    Rodent-infested fiberglass has not degraded, nor has wet cellulose. Those are external failures acting upon the insulation causing it to need replacement. If not for the rodents or the moisture failure, the insulation would be fine.

    According to NACHI, the life expectancy for most insulation is 100+ years.

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