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 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.

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 (F° · sq.ft. · hr/Btu)
 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
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
Sandstone / Limestone1"0.08
Aluminum / Vinyl (not insulated)0.61
Aluminum / Vinyl (1/2" insulation) 1.80
Carpet with fiber pad2.08
Carpet with rubber pad1.23
Asphalt Shingles0.44
Wood Shingles0.97
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
Wood, solid core1 3/4"2.17
Solid insulated metal door, polystyrene insulation
ASTM C518 Calculated
1.5" - 2"6.00 - 7.00
Solid insulated metal door, polystyrene insulation
ASTM C1363 Operable
1.5" - 2"2.20 - 2.80
Solid insulated metal door, polyurethane insulation
ASTM C518 Calculated
1.5" - 2"10.00 - 11.00
Solid insulated metal door, polyurethane insulation
ASTM C1363 Operable
1.5" - 2"2.50 - 3.50

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.

Doors and Assemblies

In the chart above, you will notice that there are two vastly different R-values provided for insulated metal doors with polyurethane insulation. Based on ASTM C518 (Calculation Method) the door has an R-value of up to 11, but using ASTM C1363 (Tested/Operable) the same door only have an R-value of up to 3.5. This is a huge difference and essentially comes down to ASTM C518 being a theoretical maximum based on a steady-state thermal test of only a portion of the door panel. However, we all know that the frame, gasketing, and, hardware will significantly affect the thermal transmittance. So a new standard test has been implemented, ASTM C1363, which tests the entire door assembly including the frame and hardware.

The results of ASTM C1363 are much lower, but are much more accurate to the actual installed conditions. In fact, the doors are performing the same as before – it is just that the R-values are much more in line with how the door really performs. Many architects are now specifying doors with the ASTM C1363 test as the standard for thermal transmittance. It is expected that other products will follow suit.

For more information, check out the Steel Door Institute's article Why Have Thermal Performance Ratings Changed?

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Insulation Manufacturers

The links below will take you to Archimat, our building product directory, which hosts a list of manufacturers.

Thermal Insulation

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