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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Here’s links to some of our other articles about INSULATION: 

 Why is the garage so hot in the summer?

How can I tell if a house has insulation? 

Why is vermiculite attic insulation a problem for both buyers and sellers of a home? 

Why is spray foam used for attic insulation?

Should I wrap the water heater with an insulation blanket? 

Should I put some more insulation in the attic?

• What does the "R-Value" of home insulation mean? 

• Is pipe insulation flammable?

• What is minimum requirement for the insulation of a mobile/manufactured home according to the HUD-code? 

• Why is insulation not allowed to touch around a gas flue in the attic even if it’s not flammable?

 Is cellulose insulation flammable? 

What does the U-value of insulation mean?  

• Does code require water pipes in the attic to be insulated? 

• Does code require water pipes in a crawl space to be insulated?

• Does a home inspector check insulation? 

Does the code require a barrier/well around the attic access hatch for blown insulation?

    Visit our ROOF AND ATTIC and INSULATION pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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