Insulation · Field guide
Insulation R-Value by US Climate Zone: Retrofit References
ENERGY STAR publishes attic retrofit references with separate columns for bare attics and attics with 3–4 inches of existing insulation. Preserve that distinction when selecting a planning target.
By Alish Gautam, Software Developer · Updated
Put the measurements to work
Open Attic Insulation Calculator →
Enter your project and product dimensions to see the net requirement, allowance and rounded purchase quantity.
Read the published reference table
| ENERGY STAR zone | Uninsulated attic | Existing 3–4 in case |
|---|---|---|
| 1 | R30 | R25 |
| 2 | R49 | R38 |
| 3 | R49 | R38 |
| 4A / 4B | R60 | R49 |
| 4C / 5 / 6 | R60 | R49 |
| 7 / 8 | R60 | R49 |
These are the two cases shown on the linked ENERGY STAR page, verified 4 October 2026. They are retrofit guidance, not a determination of the code adopted for your address. The page identifies its 2021 IECC Table R402.1.3 basis.
Do not confuse a case with a material chart
Confirm climate zone through the applicable project or local authority reference. A climate-zone thermal recommendation does not supply bags, pack coverage or product R per inch. Use a current product chart after establishing the required assembly outcome.
The attic tool accepts a custom total target and a known or estimated existing R, then reports the deficit explicitly. Interpret the published existing-insulation case with its source context; do not silently convert every value into an extra thickness or a locally binding requirement.
Check the assembly pathway
Ceilings, walls and floors have different reference values and installation conditions. Continuous insulation and cavity insulation are not interchangeable labels for whole-wall performance. Local amendments, project type and code edition can affect compliance. Keep the code/energy reference separate from manufacturer coverage and the user’s waste allowance. An area takeoff alone cannot establish whether an energy pathway is satisfied.
Sources and boundaries
ENERGY STAR: Recommended Home Insulation R-Values
Open the source · Web guidance; edition not stated · Reference checked 2026-10-04
Scope: US residential retrofit recommendations
Used for: Displayed climate-zone attic reference table.
Does not establish: Local adopted-code compliance; Manufacturer bag coverage.
The page states its guidance is based on 2021 IECC Table R402.1.3; preserve separate bare-attic and existing-insulation columns.