Climate Zone 1
Climate zone 1 is the IECC's "very hot, humid" zone. Under the 2021 map it covers 12 counties in 3 states, including Miami and Honolulu. Zone 1 is the hottest part of the country. Cooling dominates, so the code focuses on attic insulation and windows that block solar heat.
Insulation minimums in zone 1 (2021 IECC)
| Part of the house | 1A |
|---|---|
| Attic / ceiling | R-30 |
| Wood-frame walls | R-13, or R-10ci |
| Mass walls (block, brick) | R-3 exterior / R-4 interior |
| Floors over unheated space | R-13 |
| Basement walls | None required |
| Slab edge | None required |
| Crawl space walls | None required |
| Windows: max U-factor | No requirement |
| Windows: max SHGC | 0.25 |
"13+5ci" means R-13 between the studs plus R-5 foam board over the outside. Minimums from 2021 IECC Table R402.1.3; many areas still enforce an older edition, so check with your building department.
Existing home? ENERGY STAR recommends R-30 in an uninsulated attic, or adding R-25 if you already have 3–4 inches. The climate zone lookup works out how many inches to add for your county.
States in climate zone 1
Every county in zone 1
Open a state to see its counties. The state pages list every county's zone, including the ones in other zones.
Hawaii (5)
- Hawaii County
- Honolulu County
- Kalawao County
- Kauai County
- Maui County
Florida (4)
- Broward County
- Miami-Dade County
- Monroe County
- Palm Beach County
Texas (3)
- Cameron County
- Hidalgo County
- Willacy County
What changed in the 2021 map
4 of these counties moved here from zone 2 in the 2021 map. The 2021 code redrew the map with newer weather data; across the US, most counties that changed moved one zone warmer. If your town still enforces the 2018 or an older code, the old zone applies to permits.
Frequently asked questions
What is climate zone 1?
One of the eight US climate zones in the International Energy Conservation Code (IECC). Zone 1 is the hottest part of the country. Cooling dominates, so the code focuses on attic insulation and windows that block solar heat. It covers 12 counties in 3 states.
How much attic insulation do I need in climate zone 1?
In zone 1, the 2021 IECC calls for R-30 in the attic of a new home. For an existing home, ENERGY STAR recommends R-30 in an uninsulated attic, or adding R-25 if you already have 3–4 inches.
Which states are in climate zone 1?
Hawaii, Florida and Texas. Hawaii is entirely in zone 1.
Sources: Pacific Northwest National Laboratory, Guide to Determining Climate Zone by County (2022); 2021 IECC Table R402.1.3; ENERGY STAR. See how we calculate.