Recommended Home Insulation R–Values

Insulation levels are specified by R-Value. R-Value is a measure of insulation’s ability to resist heat traveling through it. The higher the R-Value the better the thermal performance of the insulation. The table below shows what levels of insulation are cost-effective for different climates and locations in the home.

Recommended insulation levels for retrofitting existing wood-framed buildings

US map showing recommended insulation levels for retrofitting existing wood-framed buildings
Zone
Add Insulation to Attic
Floor
If your attic is uninsulated
If you already have 3–4 inches of insulation
1
R30
R25
R13
2
R49
R38
R13
3
R49
R38
R19
4A and 4B
R60
R49
R19
6, 5, and 4C
R60
R49
R30
7 and 8
R60
R49
R38

Wall Insulation (above the ground) - Whenever exterior siding is removed on an: 

Uninsulated wood-frame wall:

  • Drill holes in the sheathing and blow insulation into the empty wall cavity before installing the new siding, and
  • Zones 3: Add R5 insulative wall sheathing beneath the new siding
  • Zones 4–8: Add R5 to R10 insulative wall sheathing beneath the new siding.

OR

Insulated 2x4 wood-frame wall:

  • For Zones 4–8: Add R10 insulative wall sheathing beneath the new siding.

Basement or Crawlspace Wall Insulation:

  • Zone 3: Add R5 insulative wall sheathing or R13 batt.
  • Zones 4A and 4B: Add R10 insulative wall sheathing or R13 batt.
  • Zones 4C and 5–8: Add R15 insulative wall sheathing or R19 batt.

Note: This guidance is based on the 2021 International Energy Conservation Code (IECC) Residential Provisions Chapter 4 Table R402.1.3. See Code for more detailed guidance.

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