IMPROVING ENERGY PERFORMANCE OF STEEL STUD WALLS

Steel Framing Can Perform As Well As Wood

 

 

Jan Kosny, Jeffrey E. Christian , and  André O. Desjarlais

Oak Ridge National Laboratory, Buildings Technology Center

 

 

 

ABSTRACT:

 

Steel stud wall systems for residential and commercial buildings are gaining in popularity.  Very strong thermal bridges caused by highly conductive steel studs degrade the thermal performance of such walls. Several wall configurations have been developed to improve their thermal performance. The authors tried to evaluate some of these wall systems.

 

Very often, thermal performance of the steel stud wall is compared with wood stud wall. A reduction of the in-cavity R-value caused by the wood studs is about 10% in wood stud walls. In steel stud walls, thermal bridges generated by the steel components, reduce their thermal performance by up to 55%.  Today, steel stud walls are believed to be considerably less thermally effective than similar systems made of wood because steel has a much higher thermal conductivity than wood. Relatively high R-values may be achieved by installing insulating sheathing, which is now widely recommended as the remedy for a weak thermal performance of steel stud walls.

 

A series of the promising steel stud wall configurations were analyzed. Some of these walls were designed and tested by the authors, some were tested in other laboratories, and some were developed and forgotten a long time ago. Several types of thermal breaking systems were used in these walls:

 

•        Insulating sheathing;

•        Several types of distance washers (spacers) to reduce contact area between the steel studs and exterior sheathing;

•        Reflective surfaces were added to spacer systems to improve R-value of air space;

•        Studs with reduced stud depth area or two rows of studs;

•        Several unconventional shapes of studs;

•        Local foam insulation for studs, and

•        A novel concept of combined foam/steel studs.

 

Two- and three-dimensional finite difference computer simulations were used to analyze twenty steel stud wall configurations. Also, a series of ASTM C 236 hot-box tests were conducted on several of these walls.  Test results for twenty-two additional steel stud walls were analyzed. Most of these walls contained conventional C-shape steel studs. Commonly used fiberglass and EPS were used as an insulation material. In many of the tested walls, the R-value exceeded 16 hft2F/Btu (2.81 m2K/W). The most promising steel stud wall configurations have reductions of the center of cavity R-values below 20%.

 

 

1.  INTRODUCTION

 

Steel stud wall systems for residential buildings are gaining in popularity in the United States. Unfortunately, due to the significant thermal bridging potential created by steel components, such walls, if they are not suitably designed, could lead to the excessive heat transfer for building walls in the future. Based on the result of tests and computer modeling, the thermal performance of steel stud walls are discussed. Traditional thermal performance analysis focused on the wall thermal resistance that has been enriched with a novel method for evaluating the insulation material thermal efficiency. Most of the analyzed walls were of conventional construction. They consisted of the interior finish layer, wall cavity (insulated, or not), exterior sheathing layer, and exterior finish. In some test walls, novel thermal breaking systems were installed such as spacers to reduce the contact area between studs and the exterior layer of the walls. Also, a new way of insulating the studs in contact areas was considered.

 

A computer analysis of the thermal performance of steel stud walls was carried out based on the clear wall perspective.  Currently, most of the simplified thermal calculations for steel stud wall systems are based on the measured or calculated thermal performance of the flat wall area without the effect of the wall details included. In this paper, this method is called the “clear wall” method.  The clear wall is understood as the part of the wall that is free of thermal anomalies due to wall details (i.e., windows or doors' perimeters) or intersections with the other building surfaces.

 

In this paper, the analysis is based on test results and on two- and three-dimensional computer modeling. To aid in the understanding of the thermal performance of steel stud walls, a series of twenty configurations of the steel stud walls was simulated. A finite difference computer code was used to model walls.  Maps of the temperature distribution (isotherms) in walls were developed.  These isotherms were used to calculate effective R-values.  Using simulated R-values, several configurations of wall insulation were examined.

 

In many cases, commercially available steel stud wall systems were initially designed by simple replacement of wood studs, joists, headers, etc., by structurally equivalent steel components.  Steel substitutes of the wood structure are very often being installed without consideration of the difference in thermal conductivity between wood and steel. Strong thermal bridges caused by highly conductive steel components worsen thermal performance of these walls. Because steel has higher thermal conductivity than wood, intense heat transfer occurs through the steel wall components. Wall R-value reductions (Framing Effects) caused by studs (as functions of the level of exterior insulation sheathing and stud spacing) were estimated and compared for all considered cases.

 

Several wall configurations are being developed to improve steel frame system thermal performance. Some of these innovations are evaluated in this paper. The most popular way to improve the thermal performance of steel stud walls is installing exterior insulation sheathing. Some designers try to reduce thermal bridge effects generated by the steel stud by installing horizontal steel, or wooden spacers that reduce the contact area between studs and wall finish layers. Another way to minimize the contact area between studs and sheathing material is achieved by forming small dimples on the stud flange surfaces. Also, some building material producers claim that the improvement in steel stud walls’ thermal performance may be obtained by increasing the area of the holes located on the stud web. Some unconventional shapes of steel studs are discussed as well.

 

 

2.METHODS OF THERMAL ANALYSIS

 

Currently, most of the simplified thermal calculations for steel stud wall systems are based on the measured or calculated thermal performance of the flat wall area without including the effect of the wall details. Also, in this paper, the thermal performance analysis of steel stud walls were carried out based on the clear wall perspective.

 

The clear wall thermal performance analysis was focused on the wall thermal resistance, understood as a function of the wall material configuration. The clear wall R-value study was supported by the analysis of the thermal efficiency of different kinds of sheathing, and cavity insulation. The percentage reduction of center-of-cavity R-value (actual material R-value in the middle of the cavity between studs) caused by steel studs is called the Framing Effect. It was used to compare different steel stud wall systems.

 

Theoretical Clear Wall Thermal Analysis

 

Thermal bridges created by steel components in steel stud walls (i.e., studs and tracks) can have a major effect on the thermal performance of building envelopes, increasing winter heat losses and summer heat gains. In wall constructions containing steel studs, two- and three-dimensional heat transfer is taking place. That is why the analysis conducted for this paper is based on tests and two- and three-dimensional computer modeling. To support results of computer simulations, ASTM C 236 reference hot-box tests, were conducted for some of the walls. The calibrated finite difference computer code was then used to model other walls.

 

A generalized heat conduction code developed by Oak Ridge National Laboratory (ORNL), Heating 7.2, was used to analyze the thermal fields in steel stud walls [1].  The Heating 7.2 was used to solve steady-state heat conduction problems in two- or three-dimensions using Cartesian coordinates. The surface-to-environment boundary conditions were specified for both surfaces of simulated walls. The exterior wind velocity of 15 mph was assumed. According to the ASHRAE Handbook of Fundamentals [2], at the outside wall surface, thermal resistance was set at 0.17 hft2F/Btu (0.03 m2K/W) and at the inside wall surface thermal resistance of 0.68 hft2F/Btu (0.12 m2K/W) was used during computer modeling. Two-dimensional modeling was performed for most of the clear wall areas.  Three-dimensional modeling was necessary for wall configuration containing distance spacers, holes in stud depths areas, triangular studs, etc. Maps of temperatures obtained from the modeling were used to calculate average heat fluxes and wall R-values.

 

Contact resistances were not assumed during modeling, however the accuracy of Heating 7.2's ability to predict wall system R-values was verified by comparing simulation results with published test results for twenty-eight masonry, wood frame, and steel stud walls.  Ten empty two-core 12-in. (30-cm.) units reported by Valore [3], Van Geem [4], and James [5] were modeled with accuracy better than  "4 percent [6]. Similarly eight filled two-core 12-in. (30-cm.) units reported by Valore, Van Geem, and James were modeled with accuracy better than "6 percent. A 2x4 wood stud wall reported by James was modeled with accuracy better than "2 percent. The differences between laboratory test and Heating 7.2 simulation results for nine steel stud walls described by Brown [7], Strzepek [8], and Barbour [9], and ten walls tested by the authors were analyzed [10]. For three conventional steel stud walls tested by the authors, the average accuracy of computer modeling was within 2.3% [10]. Considering that the precision of the guarded hot box method is reported to be approximately 8% [11], the ability of Heating 7.2 to reproduce the experimental data is adequate to make the desired analysis.

 

 

Framing Effect (f).

 

Calculations and test results for steel frame clear wall areas show that the measured wall R-value can be considerably lower than the “center of cavity” R-value that exclude the effects of thermal bridges caused by steel studs [12,13]. However, those comparisons do not clearly show how effectively the wall materials are used. Several ways of improving thermal performance of the steel stud walls have been considered. For example, it is widely-known that, in steel stud walls, the increase of R-value may be achieved simply by installing insulating sheathing. Sometimes it is not the most effective solution. If used efficiently, insulation material should bring to the wall at least as much of the additional R-value as it is the nominal R-value of the used insulation. Unfortunately, most designers do not have sufficient analytical tools to compare possible configurations of steel stud walls. This narrows thermal performance evaluations of steel stud walls to simple comparisons of clear wall R-values.

 

An analysis of the wall R-value reduction caused by the steel studs may aid in the thermal designing of steel stud walls. A simple way to calculate this reduction is shown in Figure 1. The R-value reduction generated by the steel studs is called the framing effect," f."  The framing effect represents the reduction in wall R-value due to the thermal bridge and can be described by the following formula:

 

f =  [ 1- Rsim/Rc_cav] x 100%           

 

 

         where:

 

         Rsimul  =       simulated or experimental clear wall R-value (with studs included ), and

Rc-cav  =       R-value for layers of material (center-of-cavity R-value), excluding  thermal resistances of air spaces.

 

In several steel stud walls, the framing effect is reported between 30% – 50% [8,14], while for wood stud walls, the framing effect does not typically exceed 12% [15]. It is possible to design and build steel stud wall with the framing effect lower than 15%. This will be discussed below.

 

 

 

Hot-Box Tests of Steel Stud Walls.

 

Measurements of wall systems are typically carried out by apparatus such as the one described in ASTM C 236, Standard Test Method for "Steady-State Thermal Transmission Properties of Building Assemblies by Means of a Guarded Hot Box" [11].  A relatively large (approximately 8 x 8-ft  -  244x144-cm. or larger) cross-section of the clear wall area of the wall system is used to determine its thermal performance.  Thermal anomalies such as steel studs are typically included in the test configuration. The precision of this test method is reported to be approximately 8% [11].

 

In this paper, experimental results of guarded hot box tests for several configurations of C‑shaped steel stud walls are presented. The tests were conducted by the United States and Canadian laboratories. This collection does not represent all steel stud wall test data available in the open literature.

 

Several sheathing insulation materials and other thermal break techniques were evaluated. In some walls, thermal effectiveness of steel or wood spacers was evaluated. Wood and steel spacers were intended to reduce the contact area between studs and the exterior layer of the wall and to increase wall R-value.

 

 

3.  THERMAL BREAKING SYSTEMS FOR THERMALLY EFFICIENT STEEL STUD WALLS

 

This section focuses on the efficiency of thermal breaking systems in steel stud walls. The authors will discuss simulation and experimental results for several configurations of steel stud walls containing thermal breaking systems. Most walls were constructed in the conventional way. They consisted of the interior board layer, wall cavity (insulated, or not), exterior sheathing layer, and exterior finish. Several types of insulating techniques for steel stud walls were evaluated. In some walls, two types of spacers were used to separate studs from the sheathing material. Wood and steel spacers reduced the contact area between stud flanges and the exterior layer of the wall.  Also, the thermal performance of walls containing unconventionally shaped steel studs, or combined foam-steel studs were analyzed.

 

 

Insulating Sheathing

 

It is widely known that installing exterior insulating sheathing is one of the simplest ways to improve a thermal performance of steel stud walls. Thermal efficiency of the usage of insulating sheathing was previously analyzed by several authors [7, 8, 9, 10, 12, 3]. Insulation sheathing reduces thermal bridge effects generated by steel studs. Figure 2 is using computer modeling results to depict a relation between the thickness of the insulation sheathing and framing effect for 3-1/2-in. steel stud walls. As a result, wall R-value increases and surface temperature difference between center of cavity and steel stud area is reduced.

 

Table 1 lists the ideal and experimental thermal resistance of twelve steel stud wall systems, along with the calculated framing effect. Test walls A.1 through A.5, B.1 through B.1.B constructed of 3-5/8-in. (9.2-cm.) studs with R-11 (1.9m2K/W) fibrous cavity insulation and 1/2‑in. (1.3-cm.) gypsum board interior sheathing. Test wall M.1 consisted of 3-5/8-in. (9.2-cm.) studs, no cavity insulation, and 2-in. (5.1-cm.) thick EPS sheathings on both sides. EPS sheathing had 3/4-in. (1.9-cm.) deep notches to accommodate the steel studs. Test walls B.2 through B.2.B contained 6-in. (15.2-cm.) studs, R-19 (3.3 m2K/W) fibrous cavity insulation, and 1/2-in. (1.3-cm.) thick gypsum board.

 

 

Table 1. Thermal Break Efficiency (TBE) in 3 5/8-in. (9.2-cm.) and 6-in. (15.2-cm.) stud walls

 

Wall symbol*Steel studsExterior sheathingRidealhft2F/Btu (m2K/W)R test[hft2F/Btu] (m2K/W)f [%]
A.1. 3-5/8" (9.2-cm.), 24" o.c. (61-cm.) ½” (1.3-cm.) plywood 12.8 (2.25) 7.9 (1.39) 38.2
A.2. 3-5/8" (9.2-cm.), 24" o.c. (61-cm.) 1" (2.5-cm.) EPS 17.6 (3.1) 13.7 (2.41) 21.1
A.3. 3-5/8" (9.2-cm.), 24" o.c. (61-cm.) 1" (2.5-cm.) EPS over ½” (1.3-cm.) gypsum board 18.0 (3.17) 13.9 (2.45) 22.8
A.4. 3-5/8" (9.2-cm.), 24" o.c. (61-cm.) ½” (1.3-cm.) EPS 15.2 (2.68) 11.4 (2.01) 25.1
A.5. 3-5/8" (9.2-cm.), 24" o.c. (61-cm.) 2" (5.1-cm.) EPS 23.0 (4.05) 18.9 (3.33) 17.8
B.1. 3-5/8" (9.2-cm.), 24" o.c. (61-cm.) ½” (1.3-cm.) gypsum board 12.2 (2.15) 7.8 (1.37) 36.3
B.1.A. 3-5/8" (9.2-cm.), 24" o.c. (61-cm.) 1" (2.5-cm.) EPS over ½”(1.3-cm.) gypsum board 16.0 (2.82) 12.5 (2.2) 21.8
B.1.B. 3-5/8" (9.2-cm.), 24" o.c. (61-cm.) 1-1/2" (3.8-cm.) EPS over ½”(1.3-cm.) gypsum board 17.6 (3.10) 13.9 (2.45) 21.2
B.2. 6" (15.2-cm.), 24" o.c. (61-cm.) ½” (1.3-cm.) gypsum board 19.1 (3.36) 9.6 (1.7) 49.8
B.2.A. 6" (15.2-cm.), 24" o.c. (61-cm.) 1" (2.5-cm.) EPS over ½”(1.3-cm.) gypsum board 22.88 (4.0) 14.1 (2.5) 38.4
B.2.B. 6" (15.2-cm.), 24" o.c. (61-cm.) 1-1/2" (3.8-cm.) EPS over ½” (1.3-cm.) gypsum board 24.53 (4.3) 15.7 (2.8) 36.0
M.1 3-5/8" (9.2-cm.), 24" o.c. (61-cm.) 2" (5.1-cm.) EPS on both sides no cavity insulation 20.69 (3.6) 18.00 (3.2) 13.0

* wall configuration described in Appendix 1.

 

 

The lowest Framing Effect value - f (13%) was obtained with wall M.1 (two layers of 2-in. -5.1‑cm. thick EPS sheathing with 3/4-in. (1.9-cm.) deep notches for stud flanges and no cavity insulation). The f value of 18% was achieved with the wall A.5., were the thickest ( 2"- 5.1-cm.) layer of rigid foam sheathing was installed. The f values increase with a decrease in the thickness of the insulating sheathing. For a 3-5/8" (9.2-cm.) stud wall with ½" (1.3-cm.) thick layer of EPS sheathing, f is about 25%. For a 3-5/8" (9.2-cm.) stud wall with 1" (2.5-cm.) thick layer of EPS sheathing, f is about 22%.  For a 3-5/8" (9.2-cm.) stud wall with ½" (1.3-cm.) thick layer of plywood sheathing f value is only 38%. For 6" (15.2-cm.) stud walls, f values are 12%-15% higher than the comparable 3-5/8" (9.2-cm.) stud walls. As shown in Figure 3, additional EPS sheathing reduces the temperature difference between the center of cavity and the stud area. For walls with no sheathing (B.1 and B.2), the temperature differences between the center of cavity and the stud area are equal about 7.5oF (4.2oC), for test temperature difference between the meter and climate side of the wall of about 50oF  (28oC). When insulating sheathing is used (walls B.1.A, B.1.B, B.2.A, and B.2.B) the temperature difference between the center of cavity and the stud area was reduced to about 4oF  (2.2oC). Reduction in the temperature difference between the steel stud and the center-of-cavity diminishes the possibility of “ghosting” and aesthetic problems caused by the attraction of the dirt to cold areas of the wall surface. In this light, using an insulating sheathing can be recommended as an efficacious way of the improving the thermal performance of steel stud walls.

 

 

Reduction of the Heat Transfer Between Studs and Sheathing (Ridges in Stud Flange Area, Dimples, Wood and Steel Spacers, and Foam Tape on the Face of Stud Flanges)

 

Four ways to reduce the contact area between studs and the sheathing are discussed in this paper. Several authors report that a reduction of the contact area between studs and sheathing layers may lead to the increase of the steel stud wall R-value [9,14]. Contact area between the stud flange and the sheathing material can be simply reduced by the change of the shape of the stud flange. Sometimes it is realized in the stage of the production of steel studs, by the outward extrusion of the small protuberances (dimples), or ridges in the stud flange surface. Sheathing material in such walls is not supported exactly by the stud flange, but by the surface of these protuberances on the flange area. Also, distant spacers can be used to reduce the thermal bridge effect in steel stud walls [9]. The authors assumed that the effectiveness of the usage of furring strips in steel stud walls could be higher if they are made of the less conductive materials. Five steel stud walls (C.1, C.1.A, C.1.B, C.2, C.2.A) with wood spacers and two walls (C.3 and C.3.A) containing 6-in. studs with two vertical distance ridges on each flange were tested by the authors. A schematic of these studs is presented in Figure 4. Vertical ridges reduced contact area between studs and the sheathing material by about 95%. Traditionally constructed wall C.2.B was tested for comparison. The above three walls, and similar three with 3.5-in. thick cavity were simulated. Thermal properties of materials for the three simulated walls were assumed to be the same as the tested walls. Data from this analysis is presented in Table 2. Structural configurations of these walls are presented in Appendix 1.

 

 

Table 2. Thermal performance of the wall containing studs with vertical distance ridges

 

Wall symbol Wall construction * Test R-value [hft2 F/Btu] (m2 K/W) Simul. R-value [hft2 F/Btu] (m2 K/W) Improvement [hft2 F/Btu] (m2 K/W) Improvement [%] f [%]
C.2.B 6-in.(15.2-cm.) studs, 20 g.a.(0.1-mm.), 24 in. (61-cm.) o.c. 9.58 (1.69) 9.50 (1.67)     50.2
C.3 As C.2.B., stud with two 1/4-in. (0.64-cm.) distance ridges. 10.44 (1.84) 10.46 (1.84) 0.96 (0.17) 10.1 45.1
C.3.A As C.2.B., stud with two ½-in.(1.3-cm.) distance ridges. 11.12 (1.96) 10.63 (1.87) 1.13 (0.20) 11.9 44.3
SIM.10 3 ½-in.(8.9-cm.) studs, 20 g.a.(0.1-mm.), 24 in. (61-cm.) o.c. **   7.17 (1.26)     38.0
SIM.11 As SIM.10., stud with two 1/4-in. (0.64-cm.) distance ridges. **   7.81 (1.38) 0.64 (0.11) 8.9 32.5
SIM. 11.A As SIM.10.., stud with two 1/4-in. (0.64-cm.) distance ridges. **   7.89 (1.39) 0.72 (0.13) 10.6 31.8

* wall configuration described in Appendix 1.

* * (material properties like for wall C.2.B)

 

 

Thermal properties of materials used in walls presented in Table 2 are shown in Table 3.

 

 

 

Table 3.   Thermal properties of wall materials for 6-in.(15.2-cm.) steel stud walls tested at ORNL

 

  Wall Material Nominal Thickness in. (cm.) Actual Thickness in (cm.) Measured Thermal Conductivity Btu-in/hft2 F (W/mK)
1. Steel studs 18-g.a. (0.012) 48x10-2(0.12) 481.30 (67.4)
2. Plywood 0.50 (1.3)   0.80 (0.12)
3. Gypsum Wall Board 0.50 (1.3) 0.64 (1.63) 1.32 (0.18)
4. R-19 Paper-Faced fiberglass 6.00 (15.20   0.33 (0.05)

 

 

In the Wall C.3.A, ½-in. (1.3-cm.) ridges yield a 16% increase in R-value compared to C.2.B. In the case of Wall C.3, an increase of about 9% is noted. The thermal effectiveness of the ½-in. (1.3-cm.) and 1/4-in. (0.6-cm.) ridges are similar. As shown in Figure 5, vertical ridges on the stud flange reduce the temperature difference between the center of cavity and the stud area. For the traditional Wall C.2.B, the temperature differences between the center of cavity and the stud area are equal about 7.1 F (3.9oC), (for the test temperature difference between the meter and climate side of the wall, of about 50oF- 28oC). When studs with vertical ridges are used (walls C.3, and C.3.A), the temperature differences between the center of cavity and the stud area were reduced to about 5.1oF (2.8oC) and 4.2oF (2.3oC), respectively. For simulated walls SIM10, SIM11, and SIM11.A with 3-1/2-in. (8.9-cm.) studs, f values are 10%-12% lower than for walls with 6-in. (15.2-cm.) studs.

 

An additional four walls were modeled to examine the thermal effect of the usage of studs with the extruded dimples (0.1-in. - 0.25-cm.) on the flange surfaces. A schematic of these studs is presented in Figure 6. Extruded dimples reduced contact area between studs and the sheathing material by 89%. Traditionally constructed walls SIM12 and SIM13 were simulated to enable comparisons. All walls used 3.5-in. (8.9-cm.) studs. The wall cavity was insulated with R-11 batts. Thermal properties of materials for simulated walls are presented in Table 4. Due to the fact that thermal modeling analysis was performed before the tests, different thermal conductivities (for some materials) can be found for thermal simulations and the tests. Simulation results are presented in the Table 5. Structural configurations of these walls are presented below.

 

 

 

Table 4.  Thermal properties of wall materials for steel stud walls simulated for the study of the usage of extruded dimples on the flange surface

 

  Wall Material Nominal Thickness in (cm.) Thermal Conductivity Btu-in/hft2 F (W/mk)
1. Steel studs: 3-1/2-in. (8.9-cm.), Stud’s Flange: 1-5/8-in (4.1-cm.). 18-g.a. (0.12) 333 (46)
2. Gypsum Wall Board 0.50 (1.3) 1.11 (0.15)
3. Plywood 0.50 (1.3) 0.80 (0.11)
4. EPS 3.50 (8.9) 0.25 (0.04)
5. Fiberglass 3.50 (8.9) 0.29 (0.04)

 

 

Table 5. Thermal performance of the wall containing studs with extruded distance dimples

 

Wall symbol Wall construction * Test R-value [hft2 F/Btu] (m2 K/W) Simul. R-value [hft2 F/Btu] (m2 K/W) Improvement [hft2 F/Btu] (m2 K/W) Improvement [%]
SIM12. Plywood, traditional 3 ½ -in. (8.9-cm.) studs, R-11, gypsum board. 8.07 (1.42)     39
SIM. 12.A Plywood, traditional 3 ½ -in. (8.9-cm.) studs with distance dimples, R-11, gypsum board. 8.77 (1.54) 0.7 (0.12) 8.7 33
SIM.13. EPS, traditional 3 ½ -in. (8.9-cm.) studs, R-11, gypsum board. 10.12 (1.78)     30
SIM. 13.A. EPS, traditional 3 ½ -in. (8.9-cm.) studs with distance dimples, R-11, gypsum board. 10.73 (1.89) 0.61 (0.11) 6.0 26

* wall configuration described in Appendix 1.

 

 

Walls with EPS sheathing are thermally more effective. However, a greater improvement was observed for wall SIM13.A with plywood sheathing. In walls containing studs with distance ridges, a reduction of contact area between the stud flange and the sheathing was about 95% and improvements in R-value were about 10%. In walls containing studs with extruded distance dimples, a reduction of the contact area between the stud flange and the sheathing was 89% and improvements in R-value were also lower — about 8%. Temperature distributions on the warmer surfaces of the simulated walls ()T = 50oF - 28oC ) are depicted in Figure 7. The extruded distance dimples on the stud flange surfaces, only slightly reduced temperature of the wall surface in the place of the stud location. A greater reduction of the temperature difference between the wall surface in the center of cavity and the wall surface in the place of the stud location was caused by EPS sheathing insulation.

 

The thermal effect of the application of spacers was examined in three walls tested by another laboratory (A.6, A.7, A.14) [8], and five walls tested by the authors. The thermal break was created by installing horizontal steel or wooden furring strips (see example on Figure 8.). They separated the steel stud from the exterior sheathing and created an air cavity.  In Wall C.1.B, this cavity was filled by additional fiberglass insulation (R-7). Results or the effectiveness of spacers are presented in Table 6.

 

 

Table 6. Thermal performance of the wall containing distance spacers

 

Wall symbol Wall construction * Test R-value [hft2 F/Btu] (m2 K/W) Simul. R-value [hft2 F/Btu] (m2 K/W) Improvement [hft2 F/Btu] (m2 K/W) Improvement [%]
A.1. ½ in. (1.3-cm.) plywood, 3-5/8 (9.2-cm.) in. studs, R-11, ½-in. (1.3-cm.) gypsum board. 7.9 (1.4)     38.2
A.6. ½ in. (1.3-cm.) plywood, 7/8-in. (2.2-cm.) steel furring, 3-5/8 in. (9.2-cm.) studs, R-11, ½-in. (1.3-cm.) gypsum board. 9.3 (1.6) 1.4 (0.2) 17.7 27.2
A.2. 1-in. (2.5-cm.) EPS, 3-5/8 in. (9.2-cm.) studs, R-11, ½-in. (1.3-cm.) gypsum board. 13.7 (2.4)     21.1
A.7. 1-in. (2.5-cm.) EPS, 7/8-in. (2.2-cm.) steel furring, 3-5/8 in. (9.2-cm.) studs, R-11, ½-in. (1.3-cm.) gypsum board. 14.4 (2.5) 0.7 (0.1) 5.1 18.2
A.11. ½ in. (1.3-cm.) plywood, 6- in. (15.2-cm.) studs, R-19, ½-in. (1.3-cm.) gypsum board. 10.1 (1.8)     47.1
A.14. ½ in.(1.3-cm.) plywood, 7/8-in.(2.2-cm.) steel furring, 6- in.(15.2-cm.) studs, R-19, 7/8-in. (2.2-cm.) steel furring, ½-in. (1.3-cm.) gypsum board. 12.4 (2.2) 2.3 (0.4) 22.8 35.0
B.1. ½ in. (1.3-cm.) gypsum board, 3-5/8 in. (9.2-cm.) studs, R-11, ½-in. (1.3-cm.) gypsum board. 7.8 (1.4)     36.3
C.1. ½ in. (1.3-cm.) gypsum board, 1x2-in. (2.5x5.1-cm.) wood spacers, 3-5/8 in. (9.2-cm.) studs, R-11, ½-in. (1.3-cm.) gypsum board. 8.8 (1.5) 1.0 (0.2) 12.8 28.1
C.1.A. ½ in. (1.3-cm.) gypsum board, 1x2-in. (2.5x5.1-cm.) wood spacers, 3-5/8 in. (9.2-cm.) studs, R-11 with reflective surface, ½-in. (1.3-cm.) gypsum board. 9.8 (1.7) 2.0 (0.3) (comparison with B.1.) 25.6 (comparison with B.1.) 20.0
B.2. ½ in. (1.3-cm.) gypsum board, 6-in. (15.2-cm.) studs, R-19, ½-in. (1.3-cm.) gypsum board. 9.6 (1.7)     49.8
C.2. ½ in. (1.3-cm.) gypsum board, 1x2-in. (2.5x5.1-cm.) wood spacers, 6-in. (15.2-cm.) studs, R-19, ½-in. (1.3-cm.) gypsum board. 10.4 (1.8) 0.8 (0.1) 8.3 45.7
A.10. ½ in. (1.3-cm.) plywood, 3-5/8 in. (9.2-cm.) studs, R-11, 7/8-in. (2.2-cm.) air space, 3-5/8 in. (9.2-cm.) studs, R-11, ½-in. (1.3-cm.) gypsum board. 13.3 (2.3)     43.6
C.1.B. ½ in. (1.3-cm.) gypsum board, 1-1/2-in. (3.8-cm.) studs, R-7, 1x2-in.(2.5x5.1-cm.) wood spacers, 3-5/8 in. (9.2-cm.) studs, R-11 with reflective surface, 1/2-in.(1.3-cm.) gypsum board. 15.5 (2.7)     25.4

* wall configuration described in Appendix 1.

 

 

It can be observed in Table 6 that for all walls with wood and steel spacers, the increase in wall R-value is close to the R-value of the additional air space. The lowest Framing Effect of about 20% was noted for the two following walls: wall containing 1-in. (2.5-cm.) EPS sheathing (A.7), and wall without insulating sheathing (C.1.A) but with R-11 reflective foil face insulation. For walls with one additional air space created by steel or wooden spacers, the highest increase of R-value was observed in case of the Wall C.1.A - 2.0 hft2F/Btu (0.35 m2K/W). 6-in. (15.2-cm.) stud walls were found less efficient from 3 5/8-in. (9.2-cm.) stud walls. They are also more difficult to improve. The most complicated constructions were used for the Wall A.14 (two rows of steel spacers), Wall A.10 (two rows of studs separated by the pieces of C-shaped studs), and wall C.1.B (two rows of studs separated by the wood furring). Most insulation was used for Wall A.10 (23.57 hft2F/Btu - 4.15 m2K/W). For these complicated walls, Wall C.1.B was found most efficient - the reduction of R-value caused by steel framing was only about 25%. Also, Wall C.1.B had the highest R-value of all the walls with steel or wood distance spacers. Figure 9 depicts a temperature distribution on the warmer surfaces of the walls ()T = 50oF- 28oC) for wall systems with wood spacers tested by the authors. The contribution of spacers and a reflective surface of the insulating batts effectively reduced temperature of the wall surface at the stud location. The highest reduction of the temperature difference between the wall surface in the center of cavity and the wall surface in the place of the stud location (2.8oF -1.6oC) was observed in the Wall C.1.B where two rows of stud separated by the wooden furring were used.

 

In the Wall A.8, 3/4-in. (1.9-cm.) wide and 5/16-in. (0.8-cm.) thick silicone foam (thermal conductivity not available [9] for simulations, it was assumed as 0.25 Btu-in/hft2F - 0.04W/mK) was attached to the exterior surfaces of stud flanges. For this wall, an increase of R-value caused by silicone foam (comparing with wall A.1.) is 0.5 hft2F/Btu (0.09 m2K/W), and f = 34.3%. As shown in Table 6, for a similar wall configuration, installing distance spacers decreased f to about 28%. This indicates that installing the thin foam insulation on the stud flanges does appreciably increase the R-value or thermal efficiency.

 

 

Reduction of Heat Transfer Area in Steel Studs (Holes)

 

The thermal effect of the reduction of the stud web area caused by stud holes in the stud web is analyzed below. Two wall configurations were used during modeling: one only with a gypsum board finish, and a second one with an additional 1-in. (2.5-cm.) EPS sheathing. Small air cavities were assumed to be in holes in the stud webs. Schematics of the three modeled shapes of studs were shown in Figure 10. The first one depicts the traditional steel stud with punched 1.5x4-in. (3.8x10.2-cm.) holes with 24-in. (61-cm.) o.c. The next two represent so called expanded channel design. The efficiency of similar studs was previously tested by J.R.Sasaki [16]. Sasaki reported 50% reduction of thermal bridge effect compared with regular steel studs walls. Thermal properties of the materials used are presented in Table 7.  Results of the analysis of the effectiveness of the usage of the punched studs are displayed in Table 8.

 

 

 

Table 7. Thermal properties of wall materials for 3-5/8-in.(9.2-cm.) simulated walls containing steel studs with reduced width area

 

  Wall Material Thickness in (cm.) Thermal Conductivity Btu-in/hft2F (W/mK)
1. Steel Studs 3-5/8-in. (9.2-cm.) 48x10-2 (0.12) 333 (46)
2. Gypsum Wall Board 0.64 (1.63) 1.32 (0.18)
3. 1-in. EPS 0.96 (2.4) 0.26 (0.04)
4. R-11 Paper-Faced fiberglass 3.50 (8.9) 0.31 (0.05)

 

 

 

 

Table 8. Thermal performance of the wall containing studs with reduced width area

 

Wall symbol Wall construction * Simul. R-value [hft 2 F/Btu] (m2K/W ) Improvement [hft2F/Btu] (m2K/W ) Improvement [%] f [%]
SIM14. Gypsum board, traditional 3 5/8 -in.(9.2-cm.) studs, R-11, gypsum board. 7.28 (1.28)     41
SIM. 14.A Gypsum board, shape A 3 5/8 -in. (9.2-cm.) studs, R-11, gypsum board. 7.43 (1.31) 0.15 (0.03) 2.1 39
SIM 14.B. Gypsum board, shape B 3 5/8 -in. (9.2-cm.) studs, R-11, gypsum board. 9.89 (1.74) 2.61 (0.46) 35.9 19
SIM 14.C. Gypsum board, shape C 3 5/8 -in. (9.2-cm.) studs, R-11, gypsum board. 9.38 (1.65) 2.1 (0.37) 28.8 23
SIM.15. 1-in. (2.5-cm.) EPS over gypsum board, traditional 3 5/8 -in.(9.2-cm.) studs, R-11, gypsum board. 11.76 (2.07)     26
SIM. 15.A. 1-in. (2.5-cm.) EPS over gypsum board, shape A 3 5/8 -in.(9.2-cm.) studs, R-11, gypsum board. 11.87 (2.09) 0.11 (0.02) 0.9 25
SIM 15.B 1-in. (2.5-cm.)EPS over gypsum board, shape B 3 5/8 -in. (9.2-cm.) studs, R-11, gypsum board. 13.76 (2.42) 2.0 (0.35) 17.0 14
SIM 15.C. 1-in. (2.5-cm.) EPS over gypsum board, shape C 3 5/8 -in.(9.2-cm.) studs, R-11, gypsum board. 13,34 (2.35) 1.58 (0.28) 13.4 16

* wall configuration described in Appendix 1.

 

 

It is clearly seen that walls with reduced stud web are much more efficient than the walls with traditional studs. The amount of the reduction of the section area of the center of the stud web for shapes of studs we considered are as follows:

 

Cshape A - 16%,

Cshape B, and C  - 87.5%

 

Stud web area was reduced by 11% in shape A stud walls, 63% in shape B stud walls, and 39% in shape C stud walls. Lowest values of the Framing Effect were noted for walls containing shape B and C studs.  Assuming that walls containing studs B and C have similar thermal performance, stud C seems to be more efficient because it is stronger (stud’s web area was reduced about 50% less than in case of wall containing shape B studs). The simulation results for the expanded channel studs are similar to that reported by J.R. Sasaki [16].  In walls containing this type of stud, the thermal bridge effect was reduced by about 50%.

 

Temperature distributions on the warmer surfaces of the simulated walls  ()T = 50oF - 28oC) are shown in Figure 11. In walls containing studs with punched 1.5x4-in. (3.6x10.2-cm.) holes, the temperature differences between the wall surface in the center of cavity and the wall surface in the place of the stud location are similar as to walls containing traditional studs. For walls with expanded channels in studs, the temperature differences are about 50% lower. In walls with EPS sheathing, the temperature differences between the wall surface in the center of cavity and the wall surface in the place of the stud location are close to 3oF (1.7oC) when studs with expanded channels are used.

 

Very optimistic prognosis for the application of the punched studs can be driven from the results of the above study of the thermal effects of the reduction of the stud web area caused by holes in the stud web.  However, the lower structural integrity of such studs has to be taken into account. More theoretical and experimental research is necessary in this area.

 

In Scandinavia, a new design of stud web is proposed for steel studs. As shown on Figure 12, the web area is divided by several courses of slots. They significantly reduce effective heat conduction area on the stud web. Currently, a series of hot box tests on steel stud walls containing slotted studs have been ordered by NAHB in ORNL BTC. The preliminary test results for two walls are presented in Table 9. The first wall is conventional 2x4 steel stud wall with R-13 batt insulation. In the second wall conventional studs and tracks were replaced by slotted structural members.

 

Table 9.

Thermal performance of the wall containing slotted studs.

 

Wall construction Tested R-value [hft 2 F/Btu] Improve- ment [hft2 F/Btu] Improve-ment [%] Framing Effect [%]
OSB, traditional 3 1/2 -in. studs, R-13 batts, gypsum board. 8.1     42
OSB, slotted 3 1/2 -in. studs, R-13 batts, gypsum board. 10.1 2.0 25 27

 

 

 

 

Another way of minimizing steel stud web heat transfer is by replacing the steel web with a less-conductive material, such as plywood or oriented strand board (OSB). A novel stud design developed by the Florida Solar Energy Center (FSEC) is analyzed below (see Figure 13). FSEC's combined wood/metal studs consist of two metal flanges and a connecting web made of OSB or plywood. The FSEC wall cavity can be insulated with R-11 or R-13 fiberglass batts. For our hot-box tests, the exterior surface of the wall was finished with a 1/2-inch-thick layer of gypsum board to simulate an exterior insulated finish system (EIFS). The interior surface of the wall was finished with a ½-inch-thick layer of gypsum board. Using the FSEC studs resulted in a 39% improvement in R-value, compared to using a traditional stud; R-10.4 for FSEC wall v.s. R-7.48 for conventional steel stud wall. The framing effect for the FSEC wall was 12.9% when for the similar wall made of conventional C-shape steel studs was 37%.

 

 

 

New Shapes of Studs (Triangular Studs, Combined Foam-Steel Studs)

 

The thermal performance of four novel shapes of studs are analyzed below. A uniform wall configuration was used during modeling: gypsum board finish, R-11 cavity insulation, and plywood exterior finish. Schematics of the four modeled shapes of studs were shown in Figure 14. The first design represents the idea of the usage of triangular studs [17]. The first steel stud wall system is comprised of two rows of triangular studs (1.5x1.5-in.- 3.6x3.8-cm.) connected by 2x4-in. (5.1x10.2-cm.) steel plates (18 g.a.- 0.12-cm.) installed with 24-in. o.c. (61-cm.) or by 2x4-in. (5.1x10.2-cm.) plywood plates (0.5-in. - 1.3-cm. thick) installed with 24‑in. o.c. (61-cm.). The next three systems represent so-called combined foam-steel studs. Similar studs made of wood and insulating foam are presently used for wall assembly [18]. Thermal properties of the materials used are presented in Table 10.  Results of the analysis of the effectiveness of the usage of these studs are displayed in Table 11 (Wall SIM 14 was included in this table to enable comparisons).

 

Table 10.  Thermal properties of wall materials for simulated walls containing novel shapes of steel studs.

 

  Wall Material Thickness in (cm.) Thermal Conductivity Btu-in/hft 2 F (W/mK)
1. Steel Studs 3-5/8-in. (9.2-cm.) 48x10 -2 (0.12) 333 (46)
2. Gypsum Wall Board 0.50 (1.3) 1.11 (0.16)
3. Plywood 0.50 (1.3) 0.80 (0.11)
4. Insulating Foam - 0.17 (0.02)
5. R-11 Paper-Faced fiberglass 3.50 (8.9) 0.31 (0.04)

 

 

 

Table 11. Thermal performance of walls containing novel shapes of studs

 

Wall symbol Wall construction * Simulated R-value hft2F/Btu (m 2 K/W)f [%]
SIM14.Gypsum board, traditional 3 5/8 -in.(9.2-cm.) studs, R-11, gypsum board. 7.28 (1.28)41
SIM16. Plywood, 2 rows of triangular 1 ½ -in.(3.8-cm.) studs with steel connector, R-11, gypsum board. 8.14 (1.43)26
SIM. 16.A.Plywood, 2 rows of triangular 1 ½ -in. (3.8-cm.) studs with plywood connector, R-11, gypsum board.11.86 (2.09)6
SIM17. Plywood, combined foam-steel 3 ½ -in. (8.9-cm.) studs ( 2 rows of 2-in. -5.1-cm. Studs ), R-11, gypsum board. 8.14 (1.43)37
SIM18. Plywood, combined foam-steel 4 -in. (10.2-cm.) studs ( 2 rows of 2-in. - 5.1-cm. studs ), fiberglass cavity insulation, gypsum board. 11.86 (2.09)20
SIM19. Plywood, combined foam-steel 3 ½ -in. (8.9-cm.) studs ( 2 rows of L-shaped 1 3/4-in. - 4.4-cm. studs ), R-11, gypsum board. 12.11 (2.13)7

* wall configuration described in Appendix 1.

 

 

Walls 16 and 16.A consist of two layers of small triangular studs. If  we compare the thermal performance of walls SIM16 and 16.A with the thermal performance of the Wall A.10 ( two layers of conventional 3-5/8-in. - 9.2-cm. studs), it is seen that walls with small triangular studs are much more effective. The application of plywood plates to connect the two rows of studs can considerably increase the wall thermal performance. R-value can increase about 3.7 hft2F/Btu (0.65-m2K/W or 46%. For Wall 16.A, the Framing Effect – “f” is about 6%. That is the lower f than for the wood framed walls (about 10%) [15]. Temperature distributions on the warmer surfaces of the simulated walls containing two rows of triangular studs are shown in Figure 13 (for simulation )T = 50oF (-28oC)).  For a wall where two rows of triangular studs are connected by steel connectors, temperature difference between the wall surface in the center of cavity and the wall surface in the place of the stud location is about 7oF (3.9oC).  It is about 2oF (1.1oC) lower than walls containing traditional studs. For walls with plywood connectors, the temperature difference is only 1.4oF (0.8oC).

 

Three walls containing different combined foam-steel studs were modeled and analyzed. It was observed that the reduction of the contact area between wall finish layer and stud flange surface increases the wall thermal efficiency  (walls SIM18 and 19). The highest R-value and lowest f were observed for wall SIM19 - 12.1 hft2F/Btu (2.13-m2K/W) and 7%. Figure 12 depicts temperature distributions on the warmer surfaces of the simulated walls containing two rows of triangular studs (for simulation )T = 50oF - 28oC).  For Wall SIM17, the temperature difference between the wall surface in the center of cavity and the wall surface in the place of the stud location is about 6oF (3.3oC).  For Wall 18, the temperature difference is only 3oF (1.7oC). It is about 1oF lower than walls containing 1-in. (2.5-cm.) thick EPS sheathing and traditional studs. For Wall 19, where the contact area between the stud steel and the sheathing material is reduced about 87%, the temperature difference between the wall surface in the center of cavity and the wall surface in the place of the stud location is only 1.4oF (0.8oC).

 

This mostly theoretical study on the thermal efficiency of the different unconventional shapes of studs proved that steel framed walls can be as efficient as wood stud walls. However, detailed structural analysis for these studs is necessary. More theoretical and experimental research in this field may help in the future development of efficient steel frame wall systems.

 

Local Stud Insulation System

 

Usage of the insulating foam covering steel studs can be considered as another way of the reduction of the contact area between studs and the sheathing. Such insulation reduces also a transverse heat transfer through stud flanges. This kind of heat transfer increases heat losses in steel framed structures and were measured and reported by H. Trethoven [19]. Covering foam shapes add highly efficient  (but are relatively expensive when compared to the cost of the fiber wall insulation) thermal insulation in locations only where it is strongly needed (steel stud areas).  This reduces thermal bridge effects. At the same time, the wall cavity is insulated by traditional insulating batts. Wall M.2, containing 1-in. (2.5-cm.) thick foam shapes covering steel studs, was designed and tested by the authors in 1994 (see Figure 15). Similar idea was utilized in Finland to insulate bottom chord of steel roof trusses.

 

For “Stud Snuggler” wall built and tested at ORNL BTC thermal properties of used materials are presented in Table 12.

 

 

Table 12.  Thermal properties for wall containing foam shapes covering steel studs

 

 Wall Material Nominal Thickness in (cm.) Actual Thickness in (cm.) Measured Thermal Conductivity Btu-in/hft 2 F (W/mK)
1.Steel Studs:18-g.a. (0.12)48x10 -2 (0.12) 481 (67)
2.Plywood0.50 (1.3)   0.80 (0.11)
3.EPS 1.00 (2.5) 0.96 (2.4)0.26 (0.04)
5.R-19 Paper-Faced fiberglass6.00 (15.2)  0.33 (0.05)

 

 

Results of the analysis of the effectiveness of the wall containing 1-in. (2.5-cm.) thick insulating foam covering steel studs are displayed in Table 13.

 

 

Table 13. Thermal performance of walls containing 1-in. thick foam shapes covering steel studs

 

Wall symbolWall construction *Tested R-value hft 2 F/Btu ( m2K/W )f [%]
M.2.Plywood, 3-5/8" (9.2-cm.) studs 24" o.c.(61-cm.), covered by 1-in. (2.5-cm.) thick EPS foam, R-19 insulation batts, Plywood16.3 (2.87)13

* wall configuration described in Appendix 1.

 

 

Wall M.2 is built in a very traditional way. It does not use expensive insulating sheathing. Foam insulation is placed only in locations of strong thermal shorts generated by the steel studs. With its simplicity, high R-value (R-16), low Framing Effect (13%), and low cost, wall M.2 can be a very good example of how proper thermal designing can create effective steel stud walls performing as well as wood frame walls.

 

 

New ORNL Energy Efficient Designs - Steel Studs as Effective as Wood

 

In the last two years, ORNL’s BTC has developed two energy-efficient steel stud wall technologies. The goal—to beat the performance of traditional 2 x 6 wood stud walls—was achieved in both cases. To make the walls economically attractive compared to traditional wood-framed constructions, both new walls use only fiberglass insulation. No foam sheathing was necessary to reach or exceed R-18, the R-value of 2 x 6 wood stud walls.

 

The first wall uses 100% conventional materials. It can be built by any builder using the local Home Depot as a supply point. The R-value of this wall is about 19.  This wall was built and tested in ORNL BTC together with 2x6 wood stud wall. In both wall the same materials were used except  the framing. For both walls hot box tests were performed. Experimental R-values for both walls were within 0.1%.

 

The second nevel design uses a novel shape of steel stud. The R-value of this wall is about R-18.

 

Both novel walls have the following advantages over conventional steel stud walls:

 

• high R-value;

• very good acoustic insulation (the wall structure does not transmit vibrations);

• high fire resistance;

 

• easy assembly; and

• lack of foam sheathing.

 

Both designs were done in consultation with the North American Steel Framing Alliance. They are 100% doable, and the technologies can be easily adopted by any steel framing fabricator. For both walls, patents are pending. ORNL is looking for companies willing to introduce these technologies to the building marketplace.

 

 

4.  CONCLUSIONS

 

In this study thermal performance of more than forty different steel stud walls were analyzed. The authors tried to find an optimum remedy for the thermal performance of the conventional steel stud wall systems. We obtained results that led to the following conclusions:

 

•        It is possible to construct steel stud walls which perform as well or even better than similar wood frame walls.

 

•        Traditionally used insulating sheathing is a simple and effective way of reducing heat losses caused by steel components in steel stud walls.

 

•        Reduction of the contact area between steel studs and wall finish layers (wood or steel furring) is only effective if accompanied by the additional insulating sheathing.

 

•        Usage of the expanded channel steel studs (stud depth area reduced 40%-65%) is one of the most effective ways of improving thermal performance of steel stud walls.

 

•        Walls containing combined steel studs (two rows of small steel studs using foam or wood as a connector) can be more effective than similar wood stud walls. However such designs may be very expensive.

 

•        Walls with foam-covered steel studs perform as well as wood stud walls. The usage of the foam-covered studs can be the simplest (also cheaper than foam sheathing) way of dramatically improving the thermal performance of steel stud walls.

 

 

This experimental and theoretical study was focused on the thermal efficiency of different traditional and unconventional methods of improving steel stud wall thermal performance. It proved that steel framed walls can be as efficient as wood stud walls. However, detailed structural analysis for many of these wall configurations is necessary. More theoretical and experimental research in this field may help in the future development of energy efficient steel frame wall systems.

 

 

 

     REFERENCES

 

1.       Childs, K. W., HEATING 7.2 Users' Manual, Oak Ridge National Laboratory, ORNL/TM-12262, February 1993.

 

2.       ASHRAE, ASHRAE Handbook of Fundamentals, ASHRAE, 1993.

 

3.       Valore, R. C., Thermophysical Properties of Masonry and Its Constituents, Part II, Thermal Transmittance of Masonry, International Masonry Institute, Washington, 1988.

 

4.       Van Geem, M. G., Thermal Transmittance of Concrete Block Walls with Core Insulation, Journal of Thermal Insulation, Vol. 9,  January 1986.

 

5.       James, T. B., Manual of Heat Transmission Coefficients for Building Components, Department of Mechanical Engineering, University of Massachusetts, Amherst, Massachusetts, November 1990.

 

6.       Kosny, J., Desjarlais, A. O., Influence of Architectural Details on the Overall Thermal Performance of Residential Wall Systems, Journal of Thermal Insulation and Building Envelope, July 1994.

 

7.       Brown, W. C., Stephenson, D. G., Guarded Hot Box Measurements of the Dynamic Heat Transition Characteristics of Seven Wall Specimens: Part II,  ASHRAE TRANSACTIONS, Vol. 99, Part 1, 1993.

 

8.       Strzepek, W. R., Thermal Resistances of Steel Frame Wall Constructions Incorporating Various Combinations of Insulating Materials, Insulation Materials, Testing and Applications,      ASTM/STP 1030, 1990.

 

9.       Barbour E., Godgrow J., Kosny J., Christian J.E. Thermal Performance of Steel-Framed Walls, NAHB Research Center. Nov. 1994.

 

10.     J. Kosny, A.O. Desjarlais, J.E. Christian - “Thermal Performance of “Energy Efficient” Steel    Stud Wall Systems -ASHRAE, BETEC, U.S.DOE VI Thermal Envelope Conference, Dec.