Everything You Need to Know About Insulation’s R-Value

Spray foam insulation
R-value expresses how well insulation does its job.

How well insulation works is expressed by its R-value, which measures resistance to the flow of heat. The higher the R-value, the better it insulates per inch of thickness.

How Much Is Enough?

The amount of insulation recommended for your home is dependent on where you live, but here are some general guidelines:

  • Attic Insulation: Houses in a cold climate should have a minimum of R-49 in the attic, which is equivalent to approximately 16″ of fiberglass insulation. Warmer climates only require an R-38 or higher, or about 12″ or more.
  • Wall Insulation: While wall insulation is limited by the width of the studs, different materials provide higher or lower R-values. Fiberglass batts for standard 2×4 walls are now available in low, medium, and high-density products that range from R-11 to R-15. Sprayed foam insulation in the same wall cavity can range from an R-14 to an R-28 depending on the product that is used.
  • Floor Insulation: While there are additional considerations—such as venting and moisture problems—to take into account when you insulate under floors, the United States Department of Energy recommends an R-25 rating in cold climates and an R-11 in warmer parts of the country.

Fiberglass insulation.

Comparative Insulation R-Values

The R-value per inch for different types of insulation varies depending on the brand and how it was installed, but here are some general comparisons from the Department of Energy:

Insulation Type:R-Value per Inch:
Fiberglass (loose)2.2 – 2.9
Fiberglass (batts)2.9 – 3.8
Cellulose (loose)3.1 – 3.8
Stone Wool (loose)2.2 – 3.3
Stone Wool (batts)3.3 – 4.2
Cotton (batts)3.0 – 3.7
Cementitious (foam)2.0 – 3.9
Polyicynene (foam)3.6 – 4.3
Phenolic (foam)4.4 – 8.2
Polyisocyanurate (foam)5.6 – 8.0
Polyurethane (foam)5.6 – 8.0

Installing Insulation

You can hire a pro to install insulation, or you can install insulation yourself in rolls and batts. If the attic doesn’t have any insulation, use faced insulation, with the vapor barrier facing toward the living space, and cut the batts to fit in the space between the ceiling joists. If the attic already has a layer of insulation up to the top of the joists, use unfaced insulation, with the new batts installed perpendicular to the joists.

Blown fiberglass or cellulose insulation is usually installed by an insulation contractor, but DIY blown cellulose insulation is also available. Loose fill cellulose insulation for blowing can be purchased at home centers and blowers are available to rent.

When installing insulation, wear:

  • Gloves
  • Goggles
  • Long sleeve clothing
  • Mask or respirator

Also, don’t work in the attic during the heat of the summer, and be careful not to step through the ceiling! Spaying expandable foam insulation is a job that should be left to professionals.

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