How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manfuactured and modular homes

What does the U-value of insulation mean?

Tuesday, July 23, 2019

U-value is a measure of thermal conductivity, and is the inverse of the more-often-used R-value, which is a measure of thermal resistance. A higher U-value of an insulation material or assembly means more thermal conductivity—in other words, less insulation value. And a higher R-value means just the opposite: better insulating qualities. 

    Actually, it’s not quite that simple because U-value is a more complicated evaluation that includes consideration of convection and radiation heat losses, but they are approximately the inverse of each other. So, when evaluating insulation, a lower U-value and a higher R-value are what you want to see.

    Although U-value is often used in energy efficiency calculations, most people are only familiar with the R-value of insulation. The only place we commonly see a U-value is on the HUD data plate of a mobile home, because HUD standards are based on U-values. 


    Conversion to R-value from the data plate from an of an older mobile home shown above is simple. So, for example, the R-value of the insulation of the walls of this home is 1 divided by .048, which is approximately R-20. The ceilings would be 1/.058 = approximately R-17, and the floors are 1/.034 = approximately R-30.

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Here’s links to a some of our blog posts about INSULATION: 

• What are the common problems with attic insulation?

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

• How can I tell if a house has insulation? 

• Why is spray foam used for attic insulation?

Should I put some more insulation in the attic?

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

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

How energy efficient is a mobile home?

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

 Is cellulose insulation flammable? 

    Visit our INSULATION page 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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