The Difference Between R-Value and U-Factor

© 2007 Door & Access Systems
Publish Date: Summer 2007
Author: Joe Hetzel
Page 62

TECHNICAL TIPS

ASK JOE HETZEL

The Difference Between R-Value and U-Factor

Q: I’ve heard about a garage door’s U-factor. What is that?

A: The U-factor is a measure of a door’s ability to conduct or transmit the flow of heat from one side to the other. This is different from R-value, which is related to heat resistance.

When talking about a material, U-factor is the “inverse” of R-value. This means that a U-factor of 0.10 is equivalent to an R-value of 10.

Codes and standards show that door thermal performance is based on the U-factor of entire door assemblies. Thus, door section R-values do not indicate the complete door’s thermal performance. You cannot simply take the inverse of the section’s R-value to get U-factor for the entire door.

Right now, an entire door assembly needs to be tested in order to determine the U-factor. DASMA is working with others to develop a reliable method of computer simulating that value.