Building Thermal Bridges

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As natural gas prices and home heating costs are predicted to skyrocket this winter, home buyers are more interested - and more willing to spend money - in the energy-efficiency features of a new home.

January 01, 2003

As natural gas prices and home heating costs are predicted to skyrocket this winter, home buyers are more interested - and more willing to spend money - in the energy-efficiency features of a new home. It's easy to point to high-efficiency heating and cooling equipment, appliances and insulation.

Builders also can help reduce the amount of money their buyers must spend to heat and cool their homes by reducing the thermal bridging through wood frame walls. According to recent research by Dow Building Materials scientists, 42% of heat loss in typical homes comes from air infiltration (16%) and wood frame walls (26%). As the charts above demonstrate, adding rigid insulation to cover everything, including the wood framing, can improve the effective R-value for the building envelope.

Effective R-value for 2x4 wall with R5 Styrofoam RS insulation
Wall components
R-value through cavity
R-value through framing
Inside air film
0.68
0.68
1/2" interior gypsum
0.45
0.45
2x4 nominal stud
-
4.38
R-13 Batt insulation
13.00
-
R5 Sytrofoam
5.00
5.00
7/16" cement siding
0.53
0.53
Outside air film
0.17
0.17
Effective R-value for the entire opaque wall = 17.2
Cavity (80%) R-value = 19.83
Framing (20%) R-value = 11.21
Source: Dow Building Materials

Effective R-value for 2x6 wall with OSB sheathing & fiber-cement siding
Wall components
R-value through cavity
R-value through framing
Inside air film
0.68
0.68
1/2" interior gypsum
0.45
0.45
2x4 nominal stud
-
6.88
R-19 Batt insulation
17.80
-
7/16" OSB sheathing
0.58
0.58
Weather barrier
0.01
0.01
7/16" cement siding
0.53
0.53
Outside air film
0.17
0.17
Effective R-value for the entire opaque wall = 16.4
Cavity (80%) R-value = 20.22
Framing (20%) R-value = 9.30
Source: Dow Building Materials

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