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
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Add Insulation to Attic
If your attic is uninsulated
If you already have 3–4 inches of insulation
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.
RESOURCES
- Seal and Insulate DIY Guide (PDF, 12.8 MB)
- Tax Credits
- Home Energy Yardstick
- Home Energy Advisor
- Windows, Doors and Skylights
