13000178 - Laserfiche WebLink

Home Browse Search

�✓ Figure B.a.Wood Studs with Twvinah Gap g 5Y E ,, Figure 8.0.Woad Studs with Two-Indies of insulation it g.-r 5.15 aTT 5r — — r 4� IIIFigure 8.c.Steel Studs with a Two-Inch Gap C 3/- ■ — — 2� m1111I,, • hill! ' • Figure 8.d.Steel Studs with Two-Inches of Insulation 8 A - All studs in center Studs equally Horizontal Pr distributed members added u� Figure Se.Steel Studs with Insulation in the Frame o wood studs,steel stud# Figure 8 Wood and steel stud configuration used in thermal Figure 9 Comparison of R-values for three wood and steel- modeling framed walls (from Figures 4-6). configurations,the nominal R-value calculated for the center Five additional wall models were developed to estimate of cavity was aboutR-13.The framing effect coefficients were the effect of imperfections in installation of cavity insulation. calculated using Equation 1 and presented in Table 3 and These wall assemblies are depicted in Figures 8a through 8e. Figure 9. In these wall assemblies small air gaps between studs are As shown on Figure 9,the R-value variation was only 2%. either un-insulated, or filled with insulation. An additional In the case of steel frame walls this variation was about 8%. case was considered for steel stud assemblies where the full The ratio of the steel stud wall R-values to the R-values of space between stud flanges was also filled with insulation-as wood stud walls averaged 0.47.The framing effect coefficient shown in Figure 8e. in steel-framed assemblies averaged 62%, while the wood- The results presented in Figure 10 show that wood-frame frame walls averaged 28%. It can be seen from these results, walls are very sensitive to imperfections in installation of the that light-gage steel structures can not be designed based on cavity insulation. In case of the wood stud wall containing the one-by-one replacement method using blueprints devel- two-inch air gaps between individual studs,the R-value was oped for the wood frame houses. The use of steel framing only R-5.65 h ft2°FBTU(0.99 m2K/F9. The framing effect should be at least combined with insulating sheathing as coefficient for this wall configuration was 56%. That is very recommended by the American Iron and Steel Institute(Gitlin, close to framing effect observed for steel-framed walls-see Gupta 1997,AISI 2003). Table 3.When all these air gaps are filled with insulation,the Wall configurations with studs installed in large clusters, wall R-value increases to R-9.24 hftr°FBTU(1.63 m2K/W). are commonlyutilized in whole-buildingenergyThis is a 64%improvement. simulations, , due to the fact that it is very simple to represent any amount of In the case of steel framing,the sensitivity to imperfec- framing in that way. The data presented above demonstrate tions in insulation installation is significantly lower. In wall that this method can be used for wood-frame walls.Unfortu- configuration containing un-insulated two-inch gaps between nately,it is not true in case of steel framing,where heal transfer studs,the R-value is 3.85 (0.68 m2K/W. When the gaps are is more complex. partly-filled with insulation the clear-wall R-value is close to A series of additional simulations was performed to esti- 4.17 (0.73 maK/W). When gaps in the steel-frame wall are mate sensitivity of the clear wall R-value to the imperfections filled with insulation(as shown in Figure 8-e)the R-value is in installing cavity insulation.The installation of insulation in about 4.30(0.76 mrKIW).The difference between lowest and buildings is not always carried out as carefully as it is done in highest R-values is in case of steel stud walls about 12%. laboratory conditions. Wall studs are often off-center by an The five simulations presented in Figure 10, helped to .e inch or two.High concentrations of framing members create demonstrate how important good quality installation of the {ir spaces where batt insulation has to be custom cut and fit.At the insulation is.Thermal performance of wood stud walls can be same time these bats are not always cut precisely to fit the dramatically changed with the presence of air gaps in stud cavi- cavity.This problem doesn't exist when loose-fill insulation or ties. It is good to realize that in currently-built residential sprayed foam are used. houses,due to intense framing,about 30%to 40%of the wall Buildings X 7