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.

R-value Units

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 in an hour. In the equation below, the imperial units are shown on the left and the SI units are shown on the right.

R-value Equation (Imperial units on left, SI units on 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.

U Factor Equation

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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.

MaterialThicknessR-value
 Air Films
Exterior 0.17
Interior Wall 0.68
Interior Ceiling 0.61
 
Air Space
Minimum 1/2" up to 4"1.00
 
Building Board
Gypsum Wall Board1/2"0.45
Gypsum Wall Board5/8"0.5625
Plywood1/2"0.62
Plywood1"1.25
Fiber board sheathing1/2"1.32
Medium Density Particle Board1/2"0.53
 
Insulating Materials
R-11 Mineral Fiber with 2x4 metal studs @ 16" OC5.50
R-11 Mineral Fiber with 2x4 wood studs @ 16" OC12.44
R-11 Mineral Fiber with 2x4 metal studs @ 24" OC6.60
R-19 Mineral Fiber with 2x6 metal studs @ 16" OC7.10
R-19 Mineral Fiber with 2x6 metal studs @ 24" OC8.55
R-19 Mineral Fiber with 2x6 wood studs @ 24" OC19.11
Expanded Polystyrene (Extruded)1"5.00
Polyurethane Foam (Foamed on site)1"6.25
Polyisocyanurate (Foil Faced)1"7.20
 
Masonry and Concrete
Common Brick4"0.80
Face Brick4"0.44
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 foot1"0.52
Concrete 70 pounds per cubic foot1"0.42
Concrete 80 pounds per cubic foot1"0.33
Concrete 90 pounds per cubic foot1"0.26
Concrete 100 pounds per cubic foot1"0.21
Concrete 120 pounds per cubic foot1"0.13
Concrete 150 pounds per cubic foot1"0.07
Granite1"0.05
Sandstone / Limestone1"0.08
 
Siding
Aluminum / Vinyl (not insulated)0.61
Aluminum / Vinyl (1/2" insulation) 1.80
 
Flooring
Hardwood3/4"0.68
Tile0.05
Carpet with fiber pad2.08
Carpet with rubber pad1.23
 
Roofing
Asphalt Shingles0.44
Wood Shingles0.97
 
Glazing
Single Pane1/4"0.91
Double Pane with 1/4" air space1.69
Double Pane with 1/2" air space2.04
Double Pane with 3/4" air space2.38
Triple Pane with 1/4" air spaces2.56
Triple Pane with 1/2" air spaces3.23
 
Doors
Wood, solid core1 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.

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