Effect of Framing Factor on Clear Wall R-value for Wood and Steel Framed Walls

Abstract

In the current practice of testing and theoretical analysis of building envelope assemblies, the amount of structural members incorporated into the total wall area is commonly called a framing factor. It used to be expressed as a percent of the total wall area. Traditionally, for wood-framed walls, the framing factor has been considered to be between 10 and 14%. According to the report prepared in 2002 by Enermodal Engineering for California Energy Commission, there is 27% framing in current residential walls in California. A similar study performed by the American Society of Heating Refrigeration and Air-conditioning Engineers in 2003 has concluded an average 25% of framing factor for all US residential buildings.

In order to incorporate this finding into theoretical and experimental procedures of heat transfer analysis, representative geometries for wood and steel-framed walls need to be redefined. In this article, R-values for various percentages of framing according to different methods of calculation are examined. Also, thermal effects of various configurations of installation, structural components in wood and steel-framed walls with studs installed at 16 in. on-center (for 27% of framing) are analyzed numerically using a 3D heat conduction code. In addition, consequences of installation imperfections in cavity insulation are analyzed from a thermal perspective. The performed numerical study demonstrated significant sensitivity of some residential walls for insulation installation imperfections.

Keywords

R-value framing factor stud configuration cavity insulation

Get full access to this article

View all access options for this article.

References

Air Conditioning Contractors of America, Manual J. Residential Load Calculation, Version 8.0, ACCA.

American Iron and Steel Institute, http://www.steel.org/facts/residential.htm

ASHRAE (2001a). ASHRAE Handbook: Fundamentals, Atlanta: American Society of Heating, Refrigerating and Air-conditioning Engineers, Inc.

ASTM C-1363-97, Standard Test Method Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus, Vol 04.06.

Building Technology Center, Oak Ridge National Laboratory, http://www.ornl.gov/sci/roofs+walls/AWT/Ref/TechHome.htm

California Energy Commission (Aug. 2001). Energy standards for Residential and Non-residential Buildings, Title 24.

Carpenter, S. C. and Schumacher, Ch. (Feb. 2003). Characterization of Framing Factors for Wood-framed Low-rise Residential Buildings, ASHRAE Transactions , 109-109.

Childs, K.W. (1993). Heating 7.2 User’s Manual, Oak Ridge National Laboratory Report ORNL/TM-12262.

Chini, S. A. and Gupta, K. (1997). A Comparison between Steel and Wood Residential Framing Systems , Journal of Construction Education, 2(2).

10.

Kosny, J. and Christian, J. E. (1995). Thermal Evaluation of Several Configurations of Insulation and Structural Materials for Some Metal Stud Walls , Energy and Buildings, 157-163

11.

Kosny, J. and Desjarlais, A. O. (1994). Influence of Architectural Details in the Overall Thermal Performance of Residential Wall Systems , Journal of Thermal Insulation and Building Envelopes, 18: 53-69 .

12.

Kosny, J. and Syed, A. M. (2004). Interactive Internet-based Building Envelope Material Database for Whole-building Energy Simulation Programs , Building Envelope Conference.

13.

Residential Energy Services Network (RESNET), RESNET Home Energy Rating Standards of Practice.