Home Insulation

Home insulation is measured in R-values, with higher values indicating that it is better at insulating your home against energy loss. Insulation is added to the ceiling, walls and floors, depending on your home’s makeup and specific location.

Insulation ratings are measured in R-values per inch of thickness. An R-value tells you how well a specific type of insulation can keep heat from leaving or entering your home. Insulation R-values will vary based on the type, thickness and density of the insulation material. A higher insulation R rating will correspond to better climate control and better energy efficiency for your home. Unfortunately, a higher insulation R-value usually means a higher cost as well. 

Some installation methods vary greatly in their average R-value per inch.

Insulation MethodCommon R-Values
Blown-in/Loose Insulation2.2 – 3.8
Fiberglass Rolls2.9 – 3.8
Spray Foam Insulation3.7 – 6.5
Foam Board Insulation3 – 10
R-Values listed per inch

Within each method of home insulation, different materials will provide better R-values. For instance, with blown-in or loose materials, cellulose or stone wool is better than fiberglass, but they are more costly.

With foam (spray or board), closed-cell foam is approximately twice as better at insulating than open-cell foam.

The Use of Climate Zones

The US Department of Energy (USDoE) has broken the United States up into eight major climate regions, with additional sub-regions based on average rainfall.

Every three years, the IECC map is adjusted to move certain counties into and out of different climate zones. The latest was released in 2021. These climate zones are used to determine recommended energy-saving qualities of the amount of insulation your home should have. The minimum R-value of your home’s attic, wall and floor insulation is set by the USDoE.

This means that depending on your climate region, it may not make sense to simply add the most insulation as you can. The added cost of more energy-efficient insulation may be wasted if your local climate is mild, such as many of our southern states.

Conversely, northern “colder” states may see their energy costs rise if their insulation levels does not meet or exceed recommended values.

Climate ZoneAttic2×4 Wall2×6 WallFlooringCrawlspace
#1 / Very Hot30 – 4913 – 1519 – 211313
#2 / Hot30 – 6013 – 1519 – 211313 – 19
#3 / Warm30 – 6013 – 1519 – 212519 – 25
#4 / Mixed38 – 6013 – 1519 – 2125 – 3025 – 30
#5 / Cool49 – 6013 – 1519 – 2125 – 3025 – 30
#6 / Cold49 – 6013 – 1519 – 2125 – 3025 – 30
#7 / Very Cold49 – 6013 – 1519 – 2125 – 3025 – 30
#8 / Arctic49 – 6013 – 1519 – 2125 – 3025 – 30
Minimum & Maximum R-values per Climate Zone

How to Calculate R-Values

Attic Example

R-values of different materials can be combined to create the correct amount of insulation for your climate zone.

For example, you can layer together two batts of R19 and R30 to create an R-value of 49 in your attic.

Loose or blown-in insulation is also commonly used in the attic since it can sit on top the rafters, ceiling or OSB flooring.

You can also mix different methods of insulation together, such as a foam board on an outside wall with spray foam or batt insulation placed between the studs.

In the image shown here, we sheathed the external wall of the building with OSB, then R3 Foam Board. The OSB does not have any insulating R-value, so it is not included in our calculation. In between the studs on the interior of the house, we added R15 fiberglass rolls, which combined with the exterior foam to create an R18 rated wall.

External Wall Example