IECC Climate Zone Map: Which Zone Are You In?
The International Energy Conservation Code (IECC) divides the US into 8 climate zones. Your zone determines the minimum R-value required for each building assembly.
- Zone 1: South Florida, Hawaii — Hot-Humid
- Zone 2: Gulf Coast, Phoenix AZ, Houston TX — Hot-Humid/Dry
- Zone 3: Atlanta GA, Dallas TX, Los Angeles CA — Warm
- Zone 4: Washington DC, Kansas City MO, Seattle WA — Mixed
- Zone 5: Chicago IL, Denver CO, Indianapolis IN — Cold
- Zone 6: Minneapolis MN, Boston MA, Portland ME — Cold
- Zone 7: Northern Minnesota, Northern Montana — Very Cold
- Zone 8: Alaska — Subarctic
IECC 2021 Minimum R-Values by Zone
Exterior Walls (Wood Frame)
| Climate Zone |
2×4 Wall Min. |
2×6 Wall Min. |
Recommended Product |
| Zone 1–2 | R-13 | R-19 | R-13 or R-15 (2×4), R-19 or R-21 (2×6) |
| Zone 3 | R-13 | R-20 | R-13 or R-15 (2×4), R-21 HD (2×6) |
| Zone 4 | R-15 | R-21 | R-15 HD (2×4), R-21 HD (2×6) |
| Zone 5 | R-20 | R-21 | R-21 HD (both) |
| Zone 6–8 | R-20 | R-21+ | R-21 HD + continuous insulation |
Attic / Ceiling Insulation
| Climate Zone |
Minimum R-Value |
Recommended Product |
| Zone 1–2 | R-30 | R-30 batts |
| Zone 3 | R-38 | R-38 batts |
| Zone 4 | R-38–R-49 | R-38 or R-49 batts |
| Zone 5 | R-49 | R-49 batts |
| Zone 6–8 | R-49–R-60 | R-49 batts + additional layer |
Floor / Crawl Space Insulation
| Climate Zone |
Over Unconditioned Space |
Conditioned Crawl Wall |
| Zone 1–3 | R-13 | R-5 |
| Zone 4–5 | R-19 | R-10 |
| Zone 6–8 | R-30 | R-15 |
Key Code Notes for Contractors
- IECC 2021 wall change: Zones 4+ now require R-15 minimum for 2×4 exterior walls. R-13 is no longer code-minimum in zone 4. Many states have adopted IECC 2021 — confirm with your AHJ.
- High-density batts: R-15 HD and R-21 HD are the same physical thickness as R-13 and R-19 respectively, but denser. They fit the same cavity and are the most common way to meet zone 4+ requirements without changing framing.
- Local amendments: California (Title 24), Washington State, and several other states have adopted energy codes stricter than IECC. Always confirm with the local AHJ.
- Thermal bridging: Stud framing reduces effective R-value by 15–20%. Some codes require continuous insulation to address this. Check your jurisdiction's requirements for CI specs.
Products We Stock for Each Zone
- Zone 1–2: R-13, R-19, R-30 in stock
- Zone 3: R-13, R-15, R-21, R-38 in stock
- Zone 4: R-15 HD, R-21 HD, R-38, R-49 in stock
- Zone 5: R-21 HD, R-49 in stock
- Zone 6–8: R-21 HD, R-49 in stock — call for high-R attic solutions
Call (929) 466-1426 to confirm current stock and get a same-day quote for your project.