How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
How long does fiberglass attic insulation last?
Saturday, June 25, 2022
Fiberglass batt insulation is often cited as having an 80 to100 year life expectancy. But that assumes ideal attic conditions, which do not exist in Florida’s intense attic heat and humidity. The photo above is from a home built in 1960 and, while the insulation is still in place, it has shrunk down over time and been damaged by moisture and occasional rodents, along with being pushed around by generations of repair and installation work. The fiberglass still provides some insulation value, but it is significantly reduced. Definitely ready for replacement.
At the other end of the life expectancy prediction range, insulation contractors insist replacement is necessary after 15 to 25 years. We think that a realistic estimate is somewhere between the two, at around 40 to 50 years life expectancy.
It is often possible to add new insulation on top of the existing, deteriorated insulation. But, if you choose this solution, make sure the soffit vents don’t get covered over by the layer of added insulation. That cuts off attic ventilation, which will negate the added R-value of the new insulation by super-heating the trapped air in the summer, and can trap moisture. To learn more, see our article What are the common problems with attic insulation?
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Field Guide for Home Inspectors, a quick reference for finding the age of 154 brands of HVAC systems, water heaters, and electrical panels, plus 210 code standards for site-built and manufactured homes, and the life expectancy rating of 195 home components. Available at amazon.com for $19.95.
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