R-Values
|
R Values for Winter Conditions (Mean 40°F)
Typical Materials Used in Metal Building Construction |
| Material |
R-Value |
Material |
R-Value |
| Metal Panels |
Negligible |
0.6 lb. Density Fiberglass 3.0" |
10.0 |
| Brick - Fale |
0.44 |
0.6 lb. Density Fiberglass 3.5" |
11.0 |
| Concrete Block 4" Cylinder |
1.11 |
0.6 lb. Density Fiberglass 4.0" |
13.0 |
| Concrete Block 8" Cylinder |
1.72 |
0.6 lb. Density Fiberglass 6.0" |
19.0 |
| Poured Concrete 6" |
1.33 |
Dead Air Space - 4" |
|
| Gypsum Board - 3 / 8" |
0.32 |
- Roof Heat - Flow Up |
0.94 |
| Gypsum Board - 1 / 2" |
0.45 |
- Wall Heat - Flow Out |
1.01 |
| Plywood - 1 / 4" |
0.30 |
Surface Air Film |
|
| Plywood - 3 / 8" |
0.47 |
- Inside Roof |
0.61 |
| Glass - 1 / 8" Clear |
0.035 |
- Inside Walls |
0.68 |
| Acoustical Tile - 1 / 2" |
1.19 |
- Outside Roof and Walls |
0.17 |
| Acoustical Tile - 3 / 4" |
1.78 |
1# Thermal Block at Structural Member |
1.5 |
|
 |
|
Example |
The U-Value is commonly called for in commercial construction. U-Values are computed from "K" or "C" or "R" factors. To compute a calculated U-Value, simply add all the applicable "R" values of the construction assembly using the chart above and divide the total "R" into 1.0. Since a "K" factor is a measurement of heat transfer in 1" of homogeneous material and "C" does not include air film or construction components, the simplest addition is of "R" values.
|
Assumption |
A wall cross section is composed of an exterior metal panel, 3" thick .6 lb. density fiberglass insulation, a dead air space, and an interior finish of 3/a" Gypsum board. Determine the total resistance.
|
|
R |
| Air Surface Outside |
0.17 |
| Metal Panel |
Neg |
| 0.6 lb. Fiberglass |
10.0 |
| Dead Air Space |
1.01 |
| 3/8" Sheetrock |
0.32 |
| Air Surface Inside |
0.68 |
| Total R 12.18 |
| U = 1/R+ = 1/12.18 = 0.082 |
|
This represents the amount of heat transfer, in BTU's per hour, through one square foot of wall area for one degree Fahrenheit temperature difference. Assuming a greater variance than one degree Fahrenheit (ex. 70° inside, 30° outside), the amount of heat transfer is obtained by multiplying the calculated U-Value by the number of degrees temperature difference. In this case it would be .082 x 40, or 3.28 BTU's per hour per square foot. |
HEAT TRANSFER IS OBTAINED BY MULTIPLYING THE CALCULATED U-VALUE BY THE NUMBER OF DEGREES TEMPERATURE. |