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Table 2. Hot-Box Test Results for Wood and Steel-Framed Wall Assemblies with Studs 16 in.(40 cm)O.C. Wall Configuration Wood Stud Wall Steel Stud Wall Steel Stud Wall Base 16 in.(40 cm) Base 16 in.(40 cm) 0.75 in.(1.9 cm)XPS Clear Wall R (Hot Box Test) 9.65(1.69) 5.78(1.02) 9.37(1.65) @4t2-°F/Btu[m2K/W]) Center f Cavity 13.95(1.76) 13.95(1.76) 17.95(3.16) R-Value(h.ftc.°FBtu[m K/W]) %Difference in 30.8% 58.6% 47.8% R-Values WALL CONFIGURATIONS USED FOR THERMAL - --- -3,--� ANALYSIS l i A series of finite difference simulations were performed on 2x4(5.1x10.2-cm)wood and steel-framed walls.The first wall specimen was a copy of the framing configuration which I is traditionally used in hot-box testing.As shown on Figure 3 I the test specimen contains wood studs Stalled 16-in.(40-cm) ! !! (. o.c.with single top and bottom plates.This wall has a framing ' I factor of about 14%. At the present time, several state energy authorities are ' considering incorporation of findings of the 2002 CEC and I Le 2003 ASHRAE studies (CEC 2001A,CEC 2001B) into the I local energy performance requirements.Unfortunately,many 1 I of these codes only characterize requirements for cavity insu- 16 -j lation or a R-value/U-value through the insulation without consideration of the framing intensity or framing materials.It — --� -----8'- --- ---is a very incomplete approach!As shown in Table 2,two walls of the same in-cavity R-values may have significantly differ- Figure 3 Schematic of an 8 x 8)9(2.44 x 2.44 m)test wall ent clear wall R-values. with 16 in. spacing. The amount of framing counts in thermal performance analysis. That is why new recommendations are needed for Figure 7 shows a wall configuration with 14 studs framing material configurations in hot-box testing-to incor- centrally located. There are 2-in. gaps between each two of porate framing factors of 25% or more. To study increased centrally-located studs. This configuration was used to levels of framing within 8-ft.by 8-ft(2.44-m by 2.44-in)test analyze the effects of missing insulation in areas of high walls, six wall configurations (three wood-frame and three concentration of structural members. steel-frame walls) were analyzed to determine the effect of On the wall configuration as presented on Figure 7,spaces stud placement on the clear-wall R-value calculation. These between studs can be empty or filled with the insulation. To configurations-are shown in Figures 4,5,and 6. further evaluate the effect of a series of these 2-in. (5.1-cm) Figure 4 shows example of the wall, where studs are wide spaces between individual studs, five walls(two wood centrally located.A cluster of 14 studs is located in the center stud and three steel stud configurations)were studied as shown of the wall. This type of configuration is common among on Figures 8-a.through 8-e.These configurations represented whole-building energy modelers since it is easy to represent different options in installation of insulation.This analysis is any framing factor by adjusting the width of a single region. very important for situations where fiberglass batt insulation Figure 5 shows a configuration where studs are evenly is in use.For small cavities fiberglass bats have to be individ- distributed across the wall area.The wall shown in Figure 6 is ually measured, cut, and installed. Since it is a very labor- moreCrealistic. It contains several horizontal members, two intensive process, builders sometimes leave such small air- four-stud clusters, and two double-stud clusters. This wall / spaces without insulation. configuration is probably the best representation of current To enable comparisons between all wall configurations structural framing practice in residential buildings of the three presented onFigures 4 through 8,the following characteristics shown(Chin,Gupta 1997). were maintained in computer modeling: Buildings X 5