Energy Efficient Walls

Kelly Kissock, Ph.D., P.E.Department of Mechanical and Aerospace EngineeringUniversity of Dayton Industrial Assessment Center

Minimize Surface AreaACT2 House

Effect of Framing Bridges on Interior Wall Temperatures

2x4 and 2x6 Frame Walls2x4 stud w/ fiberglass 2x6 stud w/ fiberglassInput InputRho (hr-ft2-F/Btu) 0.17 Rho (hr-ft2-F/Btu) 0.17Rsid (hr-ft2-F/Btu) 0.81 Rsid (hr-ft2-F/Btu) 0.81Rpoly (hr-ft2-F/Btu) 7.2 Rpoly (hr-ft2-F/Btu) 7.2Stud thickness (in) 3.625 Stud thickness (in) 5.625Rstud/in (hr-ft2-F/Btu/in) 0.833 Rstud/in (hr-ft2-F/Btu/in) 0.833Ins thickness (in) 3.625 Ins thickness (in) 5.625Rins/in (hr-ft2-F/Btu/in) 3.2 Rins/in (hr-ft2-F/Btu/in) 3.2Rgyp (hr-ft2-F/Btu) 0.45 Rgyp (hr-ft2-F/Btu) 0.45Rhi (hr-ft2-F/Btu) 0.68 Rhi (hr-ft2-F/Btu) 0.68Stud spacing (in) 16 Stud spacing (in) 24Stud width (in) 1.625 Stud width (in) 1.625Calcs CalcsRstud (hr-ft2-F/Btu) 3.020 Rstud (hr-ft2-F/Btu) 4.686Rins (hr-ft2-F/Btu) 11.600 Rins (hr-ft2-F/Btu) 18.000Rt,studpath (hr-ft2-F/Btu) 12.330 Rt,studpath (hr-ft2-F/Btu) 13.996Rt,inspath (hr-ft2-F/Btu) 20.910 Rt,inspath (hr-ft2-F/Btu) 27.310frame frac 0.102 frame frac 0.068ins frac 0.898 ins frac 0.932Rt (hr-ft2-F/Btu) 19.530 Rt (hr-ft2-F/Btu) 25.657Ut (Btu/hr-ft2-F) 0.051 Ut (Btu/hr-ft2-F) 0.039 % Decrease 24%Volume Studs (in3/ft) 4.42 Volume Studs (in3/ft) 4.57 % Decrease -3%

Truss and Beam with Wet-Blown Cellulose 1996 ASHRAE Technology Award

Structural Insulated Panels (SIPs)

SIP Thermal Resistances

Thickness4 1/2" 6 1/2" 8 1/4" 10 1/4" 12 1/4"

EPS 14.4 21.6 27.9 35.1 45.9XPS 19.5 29.5 38.3 48.3 58.3Polyurethane 21.7 32.9 N/A N/A N/A

Whole-wall effective R (hr-ft2-F/Btu) for 4.5-in SIP and frame walls

Strawbale Houses

• Low embodied energy

Strawbale House

Steel Framing

• Steel conducts heat over 300 times faster than wood

• Embodied Energy (2,000-square-foot house, EBN):– Steel: 53 mmBtu– Wood: 42 mmBtu– Use phase 48-92

mmBtu/yr (EPA)

• Thermal resistance (JTM):– Rwood is 22%

greater than Rsteel

ASHRAE Correction Factors for Metal Framing

ExampleComponent R-Value

Outdoor air film (7.5 mph) 0.25Lap siding 0.811/2-inch plywood sheathing 0.62Cavity and metal stud (R-25 x 0.38 = 9.5) 9.51/2-inch gypsum board 0.45Indoor air film (still air) 0.88

Total 12.31

Correction Factor for wood framing ~ 0.90

Insulated / Uninsulated Walls

Tint,ins = 74 FTint,unins = 64 F

Insulated / Uninsulated Walls

Wood and Brick Framing

Cellulose Insulation Retrofits

Closed-cell Polyurethane Spray-on Foam Insulation

• All closed-cell polyurethane foam insulation made today is produced with a non-CFC (chlorofluorocarbon) gas as the foaming agent.

• PU foam is – water-vapor permeable– remains flexible– fire resistant– provides good air sealing

• R-3.6 to R-6.5 per inch thickness

• Soy-based, polyurethane liquid spray-foam also available.