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kid How the Same Wall Can Have Several Different R-Values: Relations Between Amount of Framing and Overall Thermal Performance in Wood and Steel-Framed Walls Jan Kosny, PhD David Yarbrough, PhD Phillip Childs Syed Azam Mohiuddin, PhD Member ASHRAE ABSTRACT Is it possible that the same wall material configuration can be described in different documents or publications with several different R-values?Is it possible that the same code R-value requirement can be satisfied by wall configurations of significantly different thermal performance characteristics? The answers to both questions is yes, it is very likely. What is even more surprising,in most cases ofwood or steel framed constructions,these confusing answers have very simple sources: the amount of framing considered for R-value analysis and the type of wall cavity insulation. This paper documents,experimental and numerical analysis of thermal effects ofvarious configurations of structural compo- nents in wood and steel-firmed walls.In addition, consequences of installation imperfections in cavity insulation on thermal performance are analyzed The main purpose of this work is to incorporate these findings into whole-building energy calculations kand initiate discussion of changes in existing code requirements for the thermal performance of walls. e INTRODUCTION significant thermal bridges compromising nominal thermal During the last two decades the Oak Ridge National performance of the cavity insulation. That is why it is so Laboratory(ORNL)Buildings Technology Center(BTC)has important to correctly evaluate the amount of framing and its tested and evaluated hundreds of building envelope technolo- thermal impact on the surrounding area. Framing factor gies using a hot-box apparatus. This collection of technical expressed as a%of the total wall area represented by the fram- information, thermal performance data, and a very unique rng members is widely used today in experimental and theo- experience in thermal analysis, combined with the fact that retical analysis. Traditionally, in hot-box testing of wood- ORNL is a government research facility that is not associated framed walls,the framing factor has been between 10 to 14%. with commercial interests,enables an objective evaluation of In practice,however,the framing factor may be much larger. the existing code requirements,thermal calculation methods, According to the report prepared in 2002 by Enermodal Engi- aad performance ratings. neering for the California Energy Commission, residential R-values or U-values have been used for decades as walls in California have an average framing factor of 27%.A measures of thermal performance of building envelope similar study performed by ASHRAE in 2003 found an aver- components. However, there have always been numerous age framing factor of 25% for all US residential buildings disagreements regarding thermal calculation methods,defini- (CEC 2001A,CEC 2001B). tions used by code documents, or required representative To better understand the interactions of different building configurations.This paper is trying to point out some potential envelope components the Whole-Wall Thermal Evaluation incongruities. This work deals with wood and steel-framed Procedure was developed (Kosny, Desjarlais 1994). The wall technologies. In both cases,framing members represent "Whole-Wall Procedure"has been used to estimate the opaque Jan Ifosny and David Yarbrough are senior staff scientists,Phillip Childs is a staff scientist and Syed Azam Mohiuddin is a post doctoral student at Oak Ridge National Laboratory,Oak Ridge, IN. ©2007 ASHRAE.