© 2003 Door & Access Systems
Publish Date: Spring 2003
Author: Joe Hetzel
Page 64


By Joe Hetzel, DASMA Technical Director

Q: I know about R-values, but lately I’ve been seeing more references to U-factors. What’s the difference?

A: Various window and door associations have recently increased efforts to label their products for energy performance. Building and energy codes now contain certain labeling requirements, including the requirement of a U-factor on a window or door as a measure of thermal performance.

Historically, the garage door industry has used R-values to show garage door thermal performance. R-value has been commonly associated with insulation products, and the industry and consumers are usually aware that a bigger R-value is better.

However, U-factors are the opposite. U is simply the reciprocal of R, or U=1/R. In other words, an R-value of 5 is equivalent to a U of 1/5 or 0.20. People using U-factors have to get used to thinking that smaller is better, like scoring for golf.

In the new garage door certification program, DASMA is considering incorporating U-factor alongside or to replace R-value. The standard ANSI/DASMA 105 is a test procedure for determining U-factors, from which R-values are derived (R=1/U). A decision may be announced by summer.