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.