The measure for judging insulating performance is called thermal resistance (R). The R-factor is used as a relative design value for materials in normal use; actual performance is dependent upon proper installation and climate. The higher the R-factor the more efficient the material and the lower the heating costs should be.
An example of this concept follows. A ski area is replacing regular glass panes with insulating glass on a section of wall. While this will reduce glass heat losses by 40%, it is not the optimal solution. Notice in the chart below that a typical six inch wall has an R-factor over 10 times that of insulating glass. If the window has a favorable exposure or esthetic value, a portable wall utilized during off hours could be constructed.
The opportunity for saving energy and money comes with a thorough knowledge of insulation and a careful analysis of existing and proposed buildings. Below the chart is a list of informative publications on the subject.
| Material & Description | Resistance |
|---|---|
| single glass (vertical & exterior) | .9 |
| insulating glass (½ inch air space) | 1.7 |
| storm windows | 1.8 |
| 8-inch concrete block (three cell, non insulated) | 1.1 |
| wood (2 by 4 fir) | 4.5 |
| typical 6-inch wall | 21. |
Recommended Reading
- Thermal Shutters and Shades
William A. Shurcliff
Brick House Publishing Co., Inc.
Andover, Ma. - Insulation Manual
NAHB Research Foundation Inc.
627 Southlawn Lane
Box 1627
Rockville, Maryland - Home Retrofit Manual
Energy Resources Center
University of Illinois at Chicago Circle
Chicago, Ill.
