Attic Floor Insulation R-Value: Floor R-Value Chart (R13-R38)

Floor insulation is an integral part of overall home insulation. Insulation of the attic floor is so vital that the DOE has specific insulation R-value recommendations for it. We are going to check the attic floor insulation R-value chart (check below).

Here’s the whole point of attic floor insulation:

Compared to the rest of the house, the attic gets a lot of sun in the summer. Even more important, in the winter, when the hot air rises, we can lose a lot of heat via the attic (significantly increasing heating costs). The only thing that stands between the attic and the rest of the house is the attic floor. Therefore it is very smart to use higher R insulation values for that floor.

attic floor loose fill insulation with r30 insulation value
Adding several inches of loose-fill insulation to insulate attic floor is a very smart move in the long run.

The DOE has published the recommended floor R-values for the attic. These floor R-values range from R13 to R38, depending on where you live. Specifically, the US has 8 climate zones; going from Zone 1 in the extreme South (South Florida) to Zone 7 and 8 in the extreme North (Alaska, North Minnesota).

Here is the DOE’s recommended attic floor R-value insulation chart:

Floor R-Value Chart For US Climate Zones

Climate Zone: Recommended Floor R-Value: States Examples:
Zone 1: R13 South Florida, Hawaii
Zone 2: R13 Florida, South Texas, South Arizona
Zone 3: R19 California, North Texas, Alabama, Georgia
Zone 4: R19 Tennessee, Kentucky, West Oregon, Virginia
Zone 5: R30 Nevada, Utah, Oregon, Nebraska, Ohio, Illinois
Zone 6: R30 New York, Montana, Wyoming, Iowa, Dakotas
Zone 7: R38 North Dakota, North Minnesota, Alaska
Zone 8: R38 North Alaska

You can check the full climate zones US map here.

Looking at the floor R-values at different climate zones, we can clearly see that:

  • In southern states, you need lower floor R-values. In Zones 1 and 2, you need R13 floor insulation, and in Zones 3 and 4 (California, Texas), you need R19 floor insulation.
  • In northern states, you need higher floor R-values. In Zones 5 and 6, you need R30 floor insulation, and in Zones 7 and 8, you would need up to R38 floor insulation.

Why are the recommended insulation R-values in the North higher?

The main goal of attic floor insulation is to prevent heat loss in the winter (cooling-related issues in the summer are secondary). That’s why it is recommended that Northern states like Minnesota and Dakotas require almost 3 times as high floor insulation R-values as Florida or even California (R13 vs R30).

insulation between floor and subfloor
There are 6-8 inches of space available between the floor rafters. These are suitable for R30 or even higher insulation.

For R13 floor insulation and R19 floor insulation, you don’t really need to invest all that much into floor insulation materials. For R30 and R38 insulation, however, you will have to use a few inches thick polyurethane spray, XPS, polystyrene boards, EPS, insulation bats, and so on.

These floor insulation materials are usually placed between the floor and the subfloor. R-values of most floor insulation materials range between R-3 and R-6 per inch. You can check the insulation materials’ R-values per inch here.

That means you will need anywhere from 5 to 10 inches of insulation for R30 floor insulation, for example.

two inches of floor insulation adding r 10
Even the smallest rafters will have about 4 inches of space for floor insulation.

With the floor R-value insulation chart, you can now determine what R insulation value you need for the attic floor. If you need any help with figuring out how much floor insulation you should use in your state, you can use the comment section below, give us a bit of info, and we can help you out.

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