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7 - ;o ences in R-values may easily exceed 30%for different levels ^ 't`m; of framing. A DOE-2.1 whole-building energy modeling exercise ` z was performed to demonstrate a magmtude of potential differ ences in heating and cooling loads'calculations performed for ' a 1500 ft2(140 me)one-story house located in Atlanta,GA or rd Minneapolis,MN.For each location,two options of wall R- lt values were considered. First option with R-value of R-12.7 h•ft2°FBTU(2.24 m2K/W)in Table 1 represents a 9.4%fram- 44 ing factor.For the second option a wall with 25%of framing # ° the R-value is R-10.5 h•frr°FBTU(1.85 m2K/W). The results of a series of DOE 2.1E whole-building energy simulations, for the house located in Atlanta, showed about 17%difference in annual heating loads generated by walls,and similarly about 18%difference in cooling loads-as discussed Figure 1 Wood stud wall assembly typically used for hot- above, wall R-values of R-12.7 h•ft2°FBTU (2.24 m2K/W) box testing. The size of the test wall is 8 x 8 ft and R-10.5 h•ft2.°FBTU(1.85 m2K/W).For Minneapolis,the (2.4 x 2.4 m). annual heating loads generated by walls were 15% different, and the difference for the cooling loads was about 18%. Qualities of construction and insulation installation play THERMAL EFFECTS OF FRAMING important roles as well.It is well known that poorly installed cavity insulation can significantly impair the thermal perfor- Ingeneral,assuming that thermal insulation perfectly fills mance of building envelope components. One of the most wallcavities,the thermal effect of framing is a function of the common problems in residential construction industry is density of framing installation(stud spacing), ratio between installation precision of structural members. It is very thermaleonduct vibes of cavity insulation and framing mate- common to find studs offset by+1 inch(2.5-cm),or locations rial, and the depth of the wall cavity. In reality,any expects- where some structural members aze misplaced, twisted, or tions regarding a perfect installation of the cavity batt buckled under structural,moisture,and thermal loads.These insulation are unrealistic,especially in areas where insulation imperfections are not important for loose-fill or spray-applied has to fit non-standard-sized wall cavities. In North America insulations.They represent a significant challenge for building framing members have relatively uniform sizes(1.-1/2-in. or envelopes insulated with factory-made bans, which are 1-5/8-in.-3.8-cm or 4.I-cm, respectively). commonly found products in the US residential market. For For wood-stud walls without foam-sheathingthe authors 16-in.(40-cm)wood framing,factory-made batts are available in regular widths of 14-1/2(36.8-cm)in and for steel framing propose the following method of estimating whole wall R- oversized batts of 16 in.(40-cm)width are produced.Similarly values:To estimate Whole-Wall R-value of a wood frame wall, for a 24 in.(61-cm)o.c.assemblies,22-1/2-in(57.1-cm)regu- for each%of the wall framing reduce the nominal center-of- lar size and 24-in.(61-cm) oversized batts are available. For cavity R-value by 1%.This method permits a quick and rela- locations with different than nominal stud spacing,batts have tively accurate estimate of the whole-wall R-value from to be precut to the size of the wall cavity. In field conditions, known center-of-cavity R-value and the framing factor. this work is not always precise.That is why it is very common To envision the effects of framing on the wood stud wall to find either un-insulated air pockets or compressed insula- IL-valuecalculations, Table 1 shows %-differences from the lion batts.It is important to know that the insulation material basic cases (with only studs included in the calculation)and industry is trying to overcome these problems by introduction two wall configurations of different framing factors. The of additional non-standard butt sizes and different installation analyzed wood frame wall is constructed with 1/2-inch (1.3- strategies. cm) thick gypsum board on one side, 1/2-in. (1.3-cm) thick HOT-BOX TESTING OF WALL ASSAMBLIES WITH OSB(Oriented Strand Board)on the other side,and R-13(2.3 24 FRAMING FACTOR m2K/W)cavity insulation.It can be seen that R-value differ- ence between wall configurations currently used for hot-box In an effort to measure the effects of framing on wall R- testing(14%of framing)and more realistic walls containing value, a series of hot-box experiments were performed on 25%of framing is close to 15%.This fact leads to the conclu- wood and steel frame assemblies. Three configurations of sion that the framing factor for a hot-box test should reflect nominal 2x4 inch(5.1x10.2-cm)wood and steel-frame walls current construction practice. For steel-framed assemblies, insulated with R-13 h•ft2•°FBTU 2.3 m2K/W(3.5-in. thick due to more complex character of heat transfer,such simpli- 8.9-cm)fiberglass batts were tested in accordance with ASTM fled calculations are not possible. However, similar differ- C 1363.These walls were constructed with 2x4 wood or steel Builtiings X 3