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.

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):

Material | R-Value (ft^{2 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 $\frac{{\text{ft}}^{\text{2}}\text{}\xb0\text{Fh}}{\text{Btu}}$ **

### 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

$\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$4$}\right.$ " 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 ft^{2 o}Fh / BTU.

#### 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.

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 | 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 | 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 | 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 | 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 | 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 | 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 |