What are R-values?
In construction, the R-value is the measurement of a material's capacity to resist heat flow from one side to the other. In simple terms, R-values measure the effectiveness of insulation and a higher number represents more effective insulation.
R-values are additive. For instance if you have a material with an R-value of 12 attached to another material with an R-value of 3, then both materials combined have an R-value of 15.
As we said before, the R-value measures the thermal resistance of a material. This can also be expressed as the temperature difference that will cause one unit of heat to pass through one unit of area over a period of time. In the equation below, the imperial units are shown on the left and the SI units are shown on the right.
What are U-factors?
Many energy modeling programs and code calculations require U-factors (sometimes called U-values) of assemblies. The U-factor is the heat transfer coefficient, which simply means that is is a measure of an assembly's capacity to transfer thermal energy across its thickness. The U-factor of an assembly is the reciprocal of the total R-value of the assembly. The equation is shown below.
Building Material R-values
The R-values for specific assemblies like doors and glazing in the table below are generalizations because they can vary significantly based on special materials that the manufacturer uses. For instance, using argon gas in a double pane insulating glass unit will dramatically improve the R-value. Consult manufacturer literature for values specific to your project.
|Minimum 1/2" up to 4"||1.00|
|Gypsum Wall Board||1/2"||0.45|
|Gypsum Wall Board||5/8"||0.5625|
|Fiber board sheathing||1/2"||1.32|
|Medium Density Particle Board||1/2"||0.53|
|R-11 Mineral Fiber with 2x4 metal studs @ 16" OC||5.50|
|R-11 Mineral Fiber with 2x4 wood studs @ 16" OC||12.44|
|R-11 Mineral Fiber with 2x4 metal studs @ 24" OC||6.60|
|R-19 Mineral Fiber with 2x6 metal studs @ 16" OC||7.10|
|R-19 Mineral Fiber with 2x6 metal studs @ 24" OC||8.55|
|R-19 Mineral Fiber with 2x6 wood studs @ 24" OC||19.11|
|Expanded Polystyrene (Extruded)||1"||5.00|
|Polyurethane Foam (Foamed on site)||1"||6.25|
|Polyisocyanurate (Foil Faced)||1"||7.20|
|Masonry and Concrete|
|Concrete Masonry Unit (CMU)||4"||0.80|
|Concrete Masonry Unit (CMU)||8"||1.11|
|Concrete Masonry Unit (CMU)||12"||1.28|
|Concrete 60 pounds per cubic foot||1"||0.52|
|Concrete 70 pounds per cubic foot||1"||0.42|
|Concrete 80 pounds per cubic foot||1"||0.33|
|Concrete 90 pounds per cubic foot||1"||0.26|
|Concrete 100 pounds per cubic foot||1"||0.21|
|Concrete 120 pounds per cubic foot||1"||0.13|
|Concrete 150 pounds per cubic foot||1"||0.07|
|Sandstone / Limestone||1"||0.08|
|Aluminum / Vinyl (not insulated)||0.61|
|Aluminum / Vinyl (1/2" insulation)||1.80|
|Carpet with fiber pad||2.08|
|Carpet with rubber pad||1.23|
|Double Pane with 1/4" air space||1.69|
|Double Pane with 1/2" air space||2.04|
|Double Pane with 3/4" air space||2.38|
|Triple Pane with 1/4" air spaces||2.56|
|Triple Pane with 1/2" air spaces||3.23|
|Wood, solid core||1 3/4"||2.17|
|Insulated metal door||2"||15.00|
The values in the table above were taken from a number of sources including: the ASHRAE Handbook of Fundamentals, ColoradoENERGY.org, and Building Construction Illustrated by Francis D.K. Ching. Other minor sources were also used. Archtoolbox does not test materials or assemblies.
CSI MasterFormat Divisions
Thermal Protection: 07 20 00