EGEE 102
Energy Conservation and Environmental Protection

Composite Wall R-Values

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Generally, walls are made up of several layers of different materials. The R-value of a composite wall is calculated by adding the effective R-values of each of the layers of the wall.

For example, the image below shows a wall made up of four layers—½ inch drywall inside for aesthetic purposes, real insulation in between the studs, ¾ inch plywood sheathing outside, and wood siding as the final exterior finish. Together, the layers of the wall are preventing heat loss.

Wall made up of four layers. The four layers are described in the paragraph above.
Diagram of a wall

We can calculate this wall’s composite R-value by adding the R-values of each layer.

  Plasterboard (1/2 inch)
+ Fiberglass (3.5 inches @ 3.70 per inch)
+ Plywood (3/4 inches)
+ Wood Siding (1/2 inch)
-----------------------------------------
Total R-Value of Composite Wall

We can find the R-values for the walls by using the table from the page about R-Values (the table is repeated below):

Building Materials and their R-Values
Material R-Value (ft2 o Fh / BTU)
Plain glass, 1/8 inch 0.03
Stone per inch 0.08
Common Brick per inch 0.20
Asphalt Roof Shingles 0.44
1/2 inch Gypsum Board (Drywall or plasterboard) 0.45
Wood Siding, 1/2 inch 0.81
Plywood, 3/4 inch 0.94
Insulating sheathing, 3/4 inch 2.06
Fiberglass, per inch (battens) 3.50
Polystyrene per inch 5.00
Polyurethane Board per inch 6.25
Cinder Block (12 inches) 1.89

  Plasterboard (1/2 inch) = 0.4524
+ Fiberglass (3.5 inches @ 3.70 per inch) = 12.95
+ Plywood (3/4 inches) = 0.94
+ Wood Siding (1/2 inch) = 0.81
-----------------------------------------
Total R-Value of Composite Wall = 15.15 ft 2  °F h Btu

Examples

Example 1

A ceiling is insulated with 0.75" plywood, 2" of polystyrene board, and a 3" layer of fiberglass. What is the R-Value for the ceiling?

Solution:

The wall consists of three layers, and all three layers together prevent the heat loss. So, we need to add the R-values of all three layers

¾" in Plywood has an R-value of 0.94
2" of polystyrene at 5.0 per inch will have an R-value of 10.00
3" of fiberglass at 3.7 per inch will have an R-value of 11.10

So the R-value of the composite wall is 22.04 ft2 oFh / BTU.

Pink insulation in the ceiling.
Pink insulation in the ceiling

Example 2

Please watch the following 1:31 video presentation about Example #2. A wall consists of 0.5” wood siding (R = 0.81), 0.75” plywood (R = 0.94), 3.5” of fiberglass (R = 13.0), and 0.5” plasterboard (R = 0.45). What is the composite R-value of the wall?

Example 3

Please watch the following 1:18 video presentation about Example #3. What is the R-value of a wall that is made up of wood siding (R = 0.81), 5” of fiberglass (R = 3.70 per inch), and a layer of 0.5” drywall (R = 0.45)?

Example 4

Please watch the following 1:44 video presentation about Example #4. A wall is made up of 8” of stone, 3” of polyurethane board, and 0.75” of plywood. Calculate the composite R-value for the wall.

Insulation Needs By Region

The United States map below shows insulation needs by region, as indicated by color and numbers.

Instructions: Click on the “zone” buttons below the map to see the U.S. Department of Energy’s Recommended Total R-Values for new construction of houses. Note that insulation R-values are different for the ceilings, walls, floor, etc.

U.S. Department of Energy recommended total R-Values for new construction houses, by regions and by various parts of the house.

Insulation Needs activity

Click here to open a text description of the Insulation Needs activity

Insulation Needs by Region

The U.S. Department of Energy released recommended total R-values for new construction houses. The info is based on regional zone and covers various parts of the house. The states within each zone are listed below, followed by a data table containing the R-values for each part of the house. The R-values are dependent on the type of heating system being used and may vary for each. Some states may lie in multiple zones.

Zone 1

States:

  • Maine
  • New Hampshire
  • Vermont
  • New York
  • Connecticut
  • Pennsylvania
  • Virginia
  • North Carolina
  • North Dakota
  • South Dakota
  • Wisconsin
  • Iowa
  • Nebraska
  • Wyoming
  • Colorado
  • Nevada
  • Arizona
Zone 1 Insulation Needs
Zone 1 Gas
Heat Pump
Fuel Oil
Electric Furnace
Attic R-49 R-49
Cathedral Ceiling R-38 R-60
Wall R-18 R-28
Floor R-25 R-25
Crawl Space R-19 R-19
Slab Edge R-8 R-8
Basement Interior R-11 R-19
Basement Exterior R-10 R-15

Zone 2

States:

  • Massachusetts
  • Rhode Island
  • New Jersey
  • Pennsylvania
  • Maryland
  • Virginia
  • Ohio
  • Indiana
  • Illinois
  • Michigan
  • Iowa
  • Kansas
  • Oklahoma
  • Colorado
  • New Mexico
  • Utah
  • Arizona
  • Nevada
  • California
  • Montana
  • Idaho
  • Alaska
Zone 2 Insulation Needs
Zone 2 Gas
Heat Pump
Fuel Oil
Electric Furnace
Attic R-49 R-49
Cathedral Ceiling R-38 R-38
Wall R-18 R-22
Floor R-25 R-25
Crawl Space R-19 R-19
Slab Edge R-8 R-8
Basement Interior R-11 R-19
Basement Exterior R-10 R-15

Zone 3

States:

  • Maryland
  • Delaware
  • Virginia
  • West Virginia
  • Ohio
  • Indiana
  • Illinois
  • Missouri
  • Kentucky
  • Tennessee
  • North Carolina
  • South Carolina
  • Georgia
  • Florida
  • Alabama
  • Mississippi
  • Louisiana
  • Arkansas
  • Oklahoma
  • Nebraska
  • Kansas
  • Texas
  • New Mexico
  • Arizona
  • Idaho
  • Oregon
  • Washington
Zone 3 Insulation Needs
Zone 3 Gas
Heat Pump
Fuel Oil
Electric Furnace
Attic R-49
Cathedral Ceiling R-38
Wall R-18
Floor R-25
Crawl Space R-19
Slab Edge R-8
Basement Interior R-11
Basement Exterior R-10

Zone 4

States:

  • Florida
  • Mississippi
  • Louisiana
  • Texas
  • New Mexico
  • California
  • Alaska
Zone 4 Insulation Needs
Zone 4 Gas
Heat Pump
Fuel Oil
Electric Furnace
Attic R-38 R-49
Cathedral Ceiling R-38 R-38
Wall R-13 R-18
Floor R-13 R-25
Crawl Space R-19 R-19
Slab Edge R-4 R-8
Basement Interior R-11 R-11
Basement Exterior R-4 R-10

Zone 5

States:

  • California
Zone 5 Insulation Needs
Zone 5 Gas Heat Pump
Fuel Oil
Electric Furnace
Attic R-38 R-38 R-49
Cathedral Ceiling R-30 R-38 R-38
Wall R-13 R-13 R-18
Floor R-11 R-13 R-25
Crawl Space R-13 R-19 R-19
Slab Edge R-4 R-4 R-8
Basement Interior R-11 R-11 R-11
Basement Exterior R-4 R-4 R-10

Zone 6

States:

  • California
  • Hawaii
Zone 6 Insulation Needs
Zone 6 Gas Heat Pump
Fuel Oil
Electric Furnace
Attic R-22 R-38 R-49
Cathedral Ceiling R-22 R-30 R-38
Wall R-11 R-13 R-18
Floor R-11 R-11 R-25
Crawl Space R-11 R-13 R-19
Slab Edge (c) R-4 R-8
Basement Interior R-11 R-11 R-11
Basement Exterior R-4 R-4 R-10