Climate Zone 8
Climate zone 8 is the IECC's "subarctic" zone. Under the 2021 map it covers 8 counties in 1 state, including Fairbanks and interior Alaska. Zone 8 has the longest, coldest winters in the US. The code uses the same minimums as zone 7.
Insulation minimums in zone 8 (2021 IECC)
| Part of the house | 8 |
|---|---|
| Attic / ceiling | R-60 |
| Wood-frame walls | R-30, or 20+5ci, or 13+10ci, or R-20ci |
| Mass walls (block, brick) | R-19 exterior / R-21 interior |
| Floors over unheated space | R-38 |
| Basement walls | R-15ci, or R-19, or 13+5ci |
| Slab edge | R-10, 4 ft deep |
| Crawl space walls | R-15ci, or R-19, or 13+5ci |
| Windows: max U-factor | U-0.30 |
| Windows: max SHGC | No requirement |
"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-60 in an uninsulated attic, or adding R-49 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 8
| State | Counties in zone 8 |
|---|---|
| Alaska | 8 of 27 |
Every county in zone 8
Open a state to see its counties. The state pages list every county's zone, including the ones in other zones.
Alaska (8)
- Denali
- Fairbanks North Star
- Nome Census Area
- North Slope
- Northwest Arctic
- Southeast Fairbanks Census Area
- Wade Hampton Census Area
- Yukon-Koyukuk Census Area
What changed in the 2021 map
One of these, Denali (AK), moved here from zone 7 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 8?
One of the eight US climate zones in the International Energy Conservation Code (IECC). Zone 8 has the longest, coldest winters in the US. The code uses the same minimums as zone 7. It covers 8 counties in 1 state.
How much attic insulation do I need in climate zone 8?
In zone 8, the 2021 IECC calls for R-60 in the attic of a new home. For an existing home, ENERGY STAR recommends R-60 in an uninsulated attic, or adding R-49 if you already have 3–4 inches.
Which states are in climate zone 8?
Alaska.
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.