ENERGY STAR recommends R49 to R60 in an uninsulated attic in most U.S. climate zones, and only R30 in the warmest. The right number depends on your zone and on how much insulation is already there.
So the chart answers one question well: how much insulation to add when you retrofit an existing wood-framed home. It doesn't replace your local building code for permitted work. Here's ENERGY STAR's table as published on October 8, 2026.
What Does an Insulation R-Value Mean?
R-value measures how well insulation resists heat moving through it, and ENERGY STAR's 2021 IECC-based chart uses it for every recommendation. ENERGY STAR explains that the higher the R-value, the better the insulation's thermal performance. Recommended levels are stated as a total R-value for the installed insulation in an attic, floor or wall, not as a per-inch figure.
So an "R49 attic" means the insulation in that attic adds up to R49, however many inches of material that takes.
What R-Value Does ENERGY STAR Recommend for Each Climate Zone?
ENERGY STAR's table recommends R30 in Zone 1, R49 in Zones 2 and 3, and R60 in Zones 4 to 8 for an uninsulated attic. If the attic already has 3 to 4 inches, it recommends R25 to R49. Floor recommendations run from R13 in Zones 1 and 2 to R38 in Zones 7 and 8.
| Climate zone (IECC) | Attic, uninsulated | Attic, already 3–4 in. | Floor |
|---|---|---|---|
| 1 | R30 | R25 | R13 |
| 2 | R49 | R38 | R13 |
| 3 | R49 | R38 | R19 |
| 4A and 4B | R60 | R49 | R19 |
| 4C, 5 and 6 | R60 | R49 | R30 |
| 7 and 8 | R60 | R49 | R38 |
ENERGY STAR says these are recommended levels for retrofitting existing wood-framed buildings, based on the 2021 International Energy Conservation Code (IECC), Table R402.1.3. The zones are IECC climate zones, which aren't the same as California's 16 building climate zones.
How Much Wall and Basement Insulation Does ENERGY STAR Recommend?
For above-ground walls, ENERGY STAR's advice applies when exterior siding comes off: blow insulation into empty cavities, then add R5 sheathing in Zone 3 or R5 to R10 in Zones 4 to 8. For basement or crawlspace walls, it lists R5 sheathing or R13 batt in Zone 3, up to R15 sheathing or R19 batt in Zones 4C to 8.
The wall guidance by situation:
- Uninsulated wood-frame wall, siding removed: drill and blow insulation into the cavity, then add R5 insulative sheathing (Zone 3) or R5 to R10 (Zones 4 to 8) under the new siding.
- Insulated 2x4 wall, siding removed: in Zones 4 to 8, add R10 insulative sheathing.
- Basement or crawlspace walls: Zone 3, R5 sheathing or R13 batt; Zones 4A and 4B, R10 sheathing or R13 batt; Zones 4C and 5 to 8, R15 sheathing or R19 batt.
Does California's Building Code Use the Same R-Values?
Not necessarily. ENERGY STAR's chart follows the national IECC, while California sets its own Energy Code (Title 24), which uses sixteen California climate zones (California Energy Commission). Permitted insulation work has to meet the local code in force, so the local building department is the authority for a specific project.
So use the chart as a guide for how much to add, and confirm code requirements with the city or county when the work needs a permit.
Is There Still a Tax Credit or Rebate for Insulation?
The federal 25C credit, which covered insulation, ended for property placed in service after December 31, 2025, according to IRS Fact Sheet FS-2025-05. Insulation installed in 2025 is claimed on the 2025 return. Local and utility rebates vary by address.
Before 25C ended after December 31, 2025, the IRS page allowed up to $1,200 a year for improvements such as insulation. For 2026 projects, the free rebate calculator checks the verified utility and local programs for a specific home. The guide to the federal home energy credits that ended covers the 2025 return rules.
Official Sources
Every R-value in this guide comes from ENERGY STAR's recommended insulation page, checked on October 8, 2026; the ended credit's limits come from the IRS page.
- ENERGY STAR: Recommended Home Insulation R-Values, the chart and wall guidance above
- California Energy Commission: climate zones, the sixteen climate zones in the California Energy Code
- IRS: Energy Efficient Home Improvement Credit, the ended 25C credit's 2025 limits
- IRS FS-2025-05, the IRS table showing when each federal credit ended
Frequently Asked Questions
What R-value should my attic have?
It depends on your climate zone and what's already there. ENERGY STAR recommends R30 in Zone 1, R49 in Zones 2 and 3, and R60 in Zones 4 to 8 for an uninsulated attic. If the attic already has 3 to 4 inches, the targets are R25, R38 and R49.
Is a higher R-value always better?
ENERGY STAR says a higher R-value means better thermal performance. Its chart lists the insulation levels it calls cost-effective for each climate zone and location in the home, from R13 floors in Zone 1 to R60 attics in Zones 4 to 8, so those levels are the reference point for a retrofit.
Are the ENERGY STAR R-values the same as California's Title 24?
No. ENERGY STAR's table is based on the 2021 International Energy Conservation Code and uses IECC climate zones. California's Title 24 energy code uses 16 California climate zones and applies to permitted work, so check requirements with your local building department.
Can I still get a tax credit for insulation?
Not for 2026 projects. The federal 25C credit ended for property placed in service after December 31, 2025 (IRS FS-2025-05). Insulation installed during 2025 can still go on the 2025 return, up to the $1,200 annual limit that applied to most improvements.
Insulating in 2026? Check the verified rebates at your address with the free rebate calculator.