Alaska Climate Zones by Borough
Alaska's 27 boroughs and census areas span climate zones 5C to 8 under the 2021 International Energy Conservation Code (IECC). Zone 7 is the most common, with 11 of the 27. For reference, Anchorage is in zone 7, Juneau is in 6A and Fairbanks is in 8.
Insulation minimums for each zone in Alaska
| Zone | Boroughs and census areas | Attic | Wood-frame walls | Floors over unheated space | Basement walls |
|---|---|---|---|---|---|
| 5C | 3 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-30 | R-15ci, or R-19, or 13+5ci |
| 6A | 5 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-30 | R-15ci, or R-19, or 13+5ci |
| 7 | 11 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-38 | R-15ci, or R-19, or 13+5ci |
| 8 | 8 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-38 | R-15ci, or R-19, or 13+5ci |
Minimums from the 2021 IECC (Table R402.1.3). Many areas still enforce an older edition, so check with your local building department. See sources.
Which energy code Alaska uses
Alaska has no statewide residential energy code; cities and counties adopt their own, so check with your local building department. Source: US Department of Energy, September 2026. Local governments can adopt newer codes or amendments. See every state's energy code.
What changed from the 2018 map
In the 2021 map, ten moved warmer (three of them by two zones) and one moved colder: Bethel Census Area (8 → 7), Denali (7 → 8), Dillingham Census Area (8 → 7), Haines (7 → 6), Juneau (7 → 6), Ketchikan Gateway (7 → 5), Kodiak Island (7 → 6), Prince of Wales-Outer Ketchikan Census Area (7 → 5), Sitka (7 → 5), Skagway-Hoonah-Angoon Census Area (7 → 6), Wrangell-Petersburg Census Area (7 → 6). If your town still enforces the 2018 or 2015 code, the older zone applies to permits.
Every borough or census area in Alaska
| Name | Zone (2021) | Zone (2018) | Details |
|---|---|---|---|
| Aleutians East | 7 | 7 | Insulation → |
| Aleutians West Census Area | 7 | 7 | Insulation → |
| Anchorage | 7 | 7 | Insulation → |
| Bethel Census Area | 7 | 8 changed | Insulation → |
| Bristol Bay | 7 | 7 | Insulation → |
| Denali | 8 | 7 changed | Insulation → |
| Dillingham Census Area | 7 | 8 changed | Insulation → |
| Fairbanks North Star | 8 | 8 | Insulation → |
| Haines | 6A | 7 changed | Insulation → |
| Juneau | 6A | 7 changed | Insulation → |
| Kenai Peninsula | 7 | 7 | Insulation → |
| Ketchikan Gateway | 5C | 7 changed | Insulation → |
| Kodiak Island | 6A | 7 changed | Insulation → |
| Lake and Peninsula | 7 | 7 | Insulation → |
| Matanuska-Susitna | 7 | 7 | Insulation → |
| Nome Census Area | 8 | 8 | Insulation → |
| North Slope | 8 | 8 | Insulation → |
| Northwest Arctic | 8 | 8 | Insulation → |
| Prince of Wales-Outer Ketchikan Census Area | 5C | 7 changed | Insulation → |
| Sitka | 5C | 7 changed | Insulation → |
| Skagway-Hoonah-Angoon Census Area | 6A | 7 changed | Insulation → |
| Southeast Fairbanks Census Area | 8 | 8 | Insulation → |
| Valdez-Cordova Census Area | 7 | 7 | Insulation → |
| Wade Hampton Census Area | 8 | 8 | Insulation → |
| Wrangell-Petersburg Census Area | 6A | 7 changed | Insulation → |
| Yakutat | 7 | 7 | Insulation → |
| Yukon-Koyukuk Census Area | 8 | 8 | Insulation → |
Source: Pacific Northwest National Laboratory, Guide to Determining Climate Zone by County: Building America and IECC 2021 Updates (2022).
Frequently asked questions
What climate zone is Alaska?
Alaska spans IECC climate zones 5C to 8; zone 7 is the most common. Find your borough or census area in the table above, or search by ZIP code.
How much attic insulation do I need in Alaska?
The 2021 IECC calls for R-60 in the attic everywhere in Alaska.
What energy code does Alaska use?
Alaska has no statewide residential energy code; cities and counties adopt their own, so check with your local building department. Source: US Department of Energy, September 2026. Local governments can adopt newer codes or amendments.
More for Alaska: Last frost dates in Alaska · Alaska planting zones · Frost line depth by state