Insulation R-Value Chart by Climate Zone
Minimum insulation for every part of a house, by climate zone, from the 2021 and 2018 International Energy Conservation Code. Plus ENERGY STAR attic targets, R-value per inch for common materials, and batt thicknesses.
2021 IECC minimum R-values
This is the model code most states adopted or are moving to (Table R402.1.3). "ci" means continuous insulation, such as foam board over the outside of the studs; "13+5ci" means R-13 in the stud cavity plus R-5 continuous. Marine zone 4 (western Washington and Oregon) uses the zone 5 row.
| Zone | Attic | Wood-frame wall | Floor | Basement wall | Slab edge | Crawl space wall | Window U-factor |
|---|---|---|---|---|---|---|---|
| 0 and 1 | R-30 | R-13, or R-10ci | R-13 | None required | None required | None required | No requirement |
| 2 | R-49 | R-13, or R-10ci | R-13 | None required | None required | None required | U-0.40 |
| 3 | R-49 | R-20, or 13+5ci, or R-15ci | R-19 | R-5ci or R-13 | R-10, 2 ft deep | R-5ci or R-13 | U-0.30 |
| 4 (except Marine) | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-19 | R-10ci or R-13 | R-10, 4 ft deep | R-10ci or R-13 | U-0.30 |
| 5 and Marine 4 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-30 | R-15ci, or R-19, or 13+5ci | R-10, 4 ft deep | R-15ci, or R-19, or 13+5ci | U-0.30 |
| 6 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-30 | R-15ci, or R-19, or 13+5ci | R-10, 4 ft deep | R-15ci, or R-19, or 13+5ci | U-0.30 |
| 7 and 8 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-38 | R-15ci, or R-19, or 13+5ci | R-10, 4 ft deep | R-15ci, or R-19, or 13+5ci | U-0.30 |
Mass walls (block, brick, ICF), skylights and solar heat gain limits are in the lookup tool results. Above 4,000 ft or in hurricane debris regions, zones 5 to 8 allow window U-0.32.
2018 IECC minimum R-values
Many states and cities still enforce the 2018 code (Table R402.1.2) or an older one. Compared with 2021, attics are one step lower (R-38 in zones 2 and 3, R-49 in zones 4 to 8) and walls in zones 4 and 5 have no R-30 option.
| Zone | Attic | Wood-frame wall | Floor | Basement wall | Slab edge | Crawl space wall | Window U-factor |
|---|---|---|---|---|---|---|---|
| 1 | R-30 | R-13 | R-13 | None required | None required | None required | No requirement |
| 2 | R-38 | R-13 | R-13 | None required | None required | None required | U-0.40 |
| 3 | R-38 | R-20, or 13+5ci | R-19 | R-5ci or R-13 | None required | R-5ci or R-13 | U-0.32 |
| 4 (except Marine) | R-49 | R-20, or 13+5ci | R-19 | R-10ci or R-13 | R-10, 2 ft deep | R-10ci or R-13 | U-0.32 |
| 5 and Marine 4 | R-49 | R-20, or 13+5ci | R-30 | R-15ci or R-19 | R-10, 2 ft deep | R-15ci or R-19 | U-0.30 |
| 6 | R-49 | 20+5ci, or 13+10ci | R-30 | R-15ci or R-19 | R-10, 4 ft deep | R-15ci or R-19 | U-0.30 |
| 7 and 8 | R-49 | 20+5ci, or 13+10ci | R-38 | R-15ci or R-19 | R-10, 4 ft deep | R-15ci or R-19 | U-0.30 |
ENERGY STAR recommendations for existing homes
If you're adding insulation to a house you already own, these are ENERGY STAR's targets. The "already has 3–4 inches" column is how much to add on top.
| Zone | Uninsulated attic | Attic with 3–4 in. already | Floor |
|---|---|---|---|
| 1 | R-30 | add R-25 | R-13 |
| 2 | R-49 | add R-38 | R-13 |
| 3 | R-49 | add R-38 | R-19 |
| 4A, 4B | R-60 | add R-49 | R-19 |
| 4C, 5, 6 | R-60 | add R-49 | R-30 |
| 7, 8 | R-60 | add R-49 | R-38 |
R-value per inch by material
Use this to turn a target R-value into a thickness. Ranges are from US Department of Energy guides; actual values depend on the product and how well it's installed.
| Material | R per inch | Inches for R-30 | Inches for R-49 |
|---|---|---|---|
| Blown fiberglass (loose fill) | 2.2–2.7 | ~12" | ~20" |
| Blown cellulose (loose fill) | 2.9–3.8 | ~9" | ~15" |
| Fiberglass batts | 2.9–3.8 | ~9" | ~15" |
| Mineral wool batts | about 3.7 | ~8" | ~13" |
| Open-cell spray foam | 3.5–3.8 | ~8" | ~14" |
| Closed-cell spray foam | 6–7 | ~5" | ~8" |
| EPS foam board | 3.8–4.4 | ~8" | ~12" |
| XPS foam board | 5 | ~6" | ~10" |
| Polyiso foam board | 5.6–8 (about 6.5 long-term) | ~5" | ~8" |
Thickness columns use a typical mid value from each range. Loose fill settles, so follow the bag's "minimum settled thickness" for your target R-value.
Batt insulation sizes
Standard fiberglass batts come 15" wide for studs 16" on center and 23" wide for 24" on center. Thickness varies slightly by brand:
| R-value | Owens Corning | Johns Manville | Fits |
|---|---|---|---|
| R-11 | 3½" | 3½" | 2×4 walls |
| R-13 | 3½" | 3½" | 2×4 walls |
| R-15 | 3½" | 3½" | 2×4 walls (high density) |
| R-19 | 6¼" | 6½" | 2×6 walls (slightly compressed), floors |
| R-21 | 5½" | 5½" | 2×6 walls (high density) |
| R-30 | 9½" | 10¼" | attics, floors over crawl spaces |
| R-38 | 12" | 13" | attics |
| R-49 | 14" | 13½" | attics |
From Owens Corning and Johns Manville product data sheets. Cathedral-ceiling versions of R-30 and R-38 are thinner (8¼" and 10¼").
Frequently asked questions
What R-value insulation do I need in my attic?
Under the 2021 energy code: R-30 in zone 1, R-49 in zones 2 and 3, and R-60 in zones 4 to 8. ENERGY STAR gives the same targets for an uninsulated attic in an existing home. Find your zone with our ZIP code lookup.
What R-value goes in a 2×4 wall?
A 2×4 stud cavity is 3½ inches deep, which fits R-13 or R-15 batts. That meets the code alone in zones 1 and 2. Colder zones need a 2×6 wall or foam board on the outside as well.
How thick is R-30 insulation?
R-30 fiberglass batts are 9½ to 10¼ inches thick depending on the brand (8¼ inches for the high-density cathedral-ceiling version). Blown fiberglass needs about 12 inches for R-30, and blown cellulose about 9½ inches.
Is a higher R-value always better?
Higher R-value means more resistance to heat flow, but the gains shrink as you add more. Going from R-11 to R-30 in an attic saves far more than going from R-49 to R-60. Air sealing first usually matters more than the last few R-values.
Last reviewed 2026-10-21. Sources: 2021 IECC Table R402.1.3, 2018 IECC Table R402.1.2, ENERGY STAR, US DOE. See how we calculate.