Montana Climate Zones by County
All 56 of Montana's counties are in climate zone 6B under the 2021 International Energy Conservation Code (IECC).
Insulation minimums in Montana (zone 6B)
| Zone | Attic | Wood-frame walls | Floors over unheated space | Basement walls |
|---|---|---|---|---|
| 6B | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-30 | 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 Montana uses
Montana enforces the 2021 IECC with amendments for homes (in effect since Jun 2022). 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
None of Montana's counties changed zone between the 2018 and 2021 maps.
Every county in Montana
| Name | Zone (2021) | Zone (2018) | Details |
|---|---|---|---|
| Beaverhead County | 6B | 6B | Insulation → |
| Big Horn County | 6B | 6B | Insulation → |
| Blaine County | 6B | 6B | Insulation → |
| Broadwater County | 6B | 6B | Insulation → |
| Carbon County | 6B | 6B | Insulation → |
| Carter County | 6B | 6B | Insulation → |
| Cascade County | 6B | 6B | Insulation → |
| Chouteau County | 6B | 6B | Insulation → |
| Custer County | 6B | 6B | Insulation → |
| Daniels County | 6B | 6B | Insulation → |
| Dawson County | 6B | 6B | Insulation → |
| Deer Lodge County | 6B | 6B | Insulation → |
| Fallon County | 6B | 6B | Insulation → |
| Fergus County | 6B | 6B | Insulation → |
| Flathead County | 6B | 6B | Insulation → |
| Gallatin County | 6B | 6B | Insulation → |
| Garfield County | 6B | 6B | Insulation → |
| Glacier County | 6B | 6B | Insulation → |
| Golden Valley County | 6B | 6B | Insulation → |
| Granite County | 6B | 6B | Insulation → |
| Hill County | 6B | 6B | Insulation → |
| Jefferson County | 6B | 6B | Insulation → |
| Judith Basin County | 6B | 6B | Insulation → |
| Lake County | 6B | 6B | Insulation → |
| Lewis and Clark County | 6B | 6B | Insulation → |
| Liberty County | 6B | 6B | Insulation → |
| Lincoln County | 6B | 6B | Insulation → |
| Madison County | 6B | 6B | Insulation → |
| McCone County | 6B | 6B | Insulation → |
| Meagher County | 6B | 6B | Insulation → |
| Mineral County | 6B | 6B | Insulation → |
| Missoula County | 6B | 6B | Insulation → |
| Musselshell County | 6B | 6B | Insulation → |
| Park County | 6B | 6B | Insulation → |
| Petroleum County | 6B | 6B | Insulation → |
| Phillips County | 6B | 6B | Insulation → |
| Pondera County | 6B | 6B | Insulation → |
| Powder River County | 6B | 6B | Insulation → |
| Powell County | 6B | 6B | Insulation → |
| Prairie County | 6B | 6B | Insulation → |
| Ravalli County | 6B | 6B | Insulation → |
| Richland County | 6B | 6B | Insulation → |
| Roosevelt County | 6B | 6B | Insulation → |
| Rosebud County | 6B | 6B | Insulation → |
| Sanders County | 6B | 6B | Insulation → |
| Sheridan County | 6B | 6B | Insulation → |
| Silver Bow County | 6B | 6B | Insulation → |
| Stillwater County | 6B | 6B | Insulation → |
| Sweet Grass County | 6B | 6B | Insulation → |
| Teton County | 6B | 6B | Insulation → |
| Toole County | 6B | 6B | Insulation → |
| Treasure County | 6B | 6B | Insulation → |
| Valley County | 6B | 6B | Insulation → |
| Wheatland County | 6B | 6B | Insulation → |
| Wibaux County | 6B | 6B | Insulation → |
| Yellowstone County | 6B | 6B | 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 Montana?
Montana is IECC climate zone 6B under the 2021 code.
How much attic insulation do I need in Montana?
The 2021 IECC calls for R-60 in the attic everywhere in Montana.
What energy code does Montana use?
Montana enforces the 2021 IECC with amendments for homes (in effect since Jun 2022). Source: US Department of Energy, September 2026. Local governments can adopt newer codes or amendments.
More for Montana: Last frost dates in Montana · Montana planting zones · Frost line depth by state