Insulation R-value chart: what the code calls for in attics, walls and floors, by climate zone
The 2021 energy code's minimums for an attic, the ceiling R-value, are R-30 in climate zones 0 and 1, R-49 in zones 2 and 3, and R-60 in zones 4 through 8. Wood-frame walls run from R-13 in the warmest zones to R-30, or R-20 plus R-5 continuous insulation, in zones 4 and colder (IECC Table R402.1.3). Your state or city may have adopted a different edition.
Anthony Hicks30+ years in construction. Updated November 5, 2026.
Reading as
The chart
Minimum R-values by climate zone (IECC Table R402.1.3):
| Climate zone | Ceiling (attic) | Wood-frame wall | Floor |
|---|---|---|---|
| 0 and 1 | R-30 | R-13, or R-10 continuous | R-13 |
| 2 | R-49 | R-13, or R-10 continuous | R-13 |
| 3 | R-49 | R-20, or R-13 + R-5 continuous | R-19 |
| 4, except Marine | R-60 | R-30, or R-20 + R-5 continuous | R-19 |
| 5 and Marine 4 | R-60 | R-30, or R-20 + R-5 continuous | R-30 |
| 6 | R-60 | R-30, or R-20 + R-5 continuous | R-30 |
| 7 and 8 | R-60 | R-30, or R-20 + R-5 continuous | R-38 |
The walls in zones 3 and colder have more ways to meet the code, such as R-13 plus R-10 continuous, or R-15 continuous alone in zone 3 and R-20 continuous alone in zones 4 through 8.
Basements, crawl spaces and slabs
| Climate zone | Basement wall | Crawl space wall | Slab edge |
|---|---|---|---|
| 0 to 2 | None | None | None |
| 3 | R-5 continuous or R-13 | R-5 continuous or R-13 | R-10, 2 feet deep |
| 4, except Marine | R-10 continuous or R-13 | R-10 continuous or R-13 | R-10, 4 feet deep |
| 5 to 8 and Marine 4 | R-15 continuous, R-19, or R-13 + R-5 continuous | Same as the basement wall | R-10, 4 feet deep |
A heated slab also gets R-5 under its full area, on top of the edge insulation, and basement walls in warm-humid locations don’t need insulation.
How to read the entries
- The R-value is the insulation’s resistance to heat flow; higher insulates more. The table’s values are minimums.
- “Continuous” (ci) is insulation that runs unbroken across the framing, such as foam board on the outside of the studs.
- “R-20 + R-5” means R-20 in the stud cavity plus R-5 continuous insulation, the cavity first.
- Compressed insulation counts as installed: where batts go into a cavity thinner than their label thickness, the R-value installed still has to meet the table.
Finding your climate zone
The energy code assigns every county a climate zone, from 0 for the hottest to 8 for the coldest, in its climate zone map and table (IECC Figure R301.1 and Table R301.1). The building department can tell you which zone and which code edition apply where you work.
Insulation in an estimate
Insulation goes on an estimate by the square foot and the R-value: blown into the attic floor, batts in the walls, or foam. The blown-in insulation cost guide and the spray foam cost guide price them by state.
Common questions
What R-value do I need in my attic?
R-30 in climate zones 0 and 1, R-49 in zones 2 and 3, and R-60 in zones 4 through 8, under the 2021 energy code (IECC Table R402.1.3).
What R-value do walls need?
R-13 in zones 0 to 2, R-20 or R-13 plus R-5 continuous in zone 3, and R-30 or R-20 plus R-5 continuous in zones 4 through 8, for wood-frame walls (IECC Table R402.1.3).
Is R-60 attic insulation required everywhere?
No. R-60 is the minimum in zones 4 through 8; warmer zones call for R-30 or R-49.
Does the code allow other ways to comply?
Yes. The R-value table is the prescriptive path; the energy code also allows meeting it by total heat loss or by a performance calculation instead (IECC R401.2).