Colorado Climate Zones by County
Colorado's 64 counties span climate zones 4B to 7 under the 2021 International Energy Conservation Code (IECC). Zone 5B is the most common, with 34 of the 64. For reference, Denver, Colorado Springs and Fort Collins are in zone 5B.
Insulation minimums for each zone in Colorado
| Zone | Counties | Attic | Wood-frame walls | Floors over unheated space | Basement walls |
|---|---|---|---|---|---|
| 4B | 5 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-19 | R-10ci or R-13 |
| 5B | 34 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-30 | R-15ci, or R-19, or 13+5ci |
| 6B | 12 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-30 | R-15ci, or R-19, or 13+5ci |
| 7 | 13 | 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 Colorado uses
Colorado 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
Three counties moved one zone warmer in the 2021 map: Bent County (5 → 4), Custer County (6 → 5), Prowers County (5 → 4). If your town still enforces the 2018 or 2015 code, the older zone applies to permits.
Every county in Colorado
| Name | Zone (2021) | Zone (2018) | Details |
|---|---|---|---|
| Adams County | 5B | 5B | Insulation → |
| Alamosa County | 6B | 6B | Insulation → |
| Arapahoe County | 5B | 5B | Insulation → |
| Archuleta County | 6B | 6B | Insulation → |
| Baca County | 4B | 4B | Insulation → |
| Bent County | 4B | 5B changed | Insulation → |
| Boulder County | 5B | 5B | Insulation → |
| Broomfield County | 5B | 5B | Insulation → |
| Chaffee County | 6B | 6B | Insulation → |
| Cheyenne County | 5B | 5B | Insulation → |
| Clear Creek County | 7 | 7 | Insulation → |
| Conejos County | 6B | 6B | Insulation → |
| Costilla County | 6B | 6B | Insulation → |
| Crowley County | 5B | 5B | Insulation → |
| Custer County | 5B | 6B changed | Insulation → |
| Delta County | 5B | 5B | Insulation → |
| Denver County | 5B | 5B | Insulation → |
| Dolores County | 6B | 6B | Insulation → |
| Douglas County | 5B | 5B | Insulation → |
| Eagle County | 6B | 6B | Insulation → |
| El Paso County | 5B | 5B | Insulation → |
| Elbert County | 5B | 5B | Insulation → |
| Fremont County | 5B | 5B | Insulation → |
| Garfield County | 5B | 5B | Insulation → |
| Gilpin County | 5B | 5B | Insulation → |
| Grand County | 7 | 7 | Insulation → |
| Gunnison County | 7 | 7 | Insulation → |
| Hinsdale County | 7 | 7 | Insulation → |
| Huerfano County | 5B | 5B | Insulation → |
| Jackson County | 7 | 7 | Insulation → |
| Jefferson County | 5B | 5B | Insulation → |
| Kiowa County | 5B | 5B | Insulation → |
| Kit Carson County | 5B | 5B | Insulation → |
| La Plata County | 5B | 5B | Insulation → |
| Lake County | 7 | 7 | Insulation → |
| Larimer County | 5B | 5B | Insulation → |
| Las Animas County | 4B | 4B | Insulation → |
| Lincoln County | 5B | 5B | Insulation → |
| Logan County | 5B | 5B | Insulation → |
| Mesa County | 5B | 5B | Insulation → |
| Mineral County | 7 | 7 | Insulation → |
| Moffat County | 6B | 6B | Insulation → |
| Montezuma County | 5B | 5B | Insulation → |
| Montrose County | 5B | 5B | Insulation → |
| Morgan County | 5B | 5B | Insulation → |
| Otero County | 4B | 4B | Insulation → |
| Ouray County | 6B | 6B | Insulation → |
| Park County | 7 | 7 | Insulation → |
| Phillips County | 5B | 5B | Insulation → |
| Pitkin County | 7 | 7 | Insulation → |
| Prowers County | 4B | 5B changed | Insulation → |
| Pueblo County | 5B | 5B | Insulation → |
| Rio Blanco County | 6B | 6B | Insulation → |
| Rio Grande County | 7 | 7 | Insulation → |
| Routt County | 7 | 7 | Insulation → |
| Saguache County | 6B | 6B | Insulation → |
| San Juan County | 7 | 7 | Insulation → |
| San Miguel County | 6B | 6B | Insulation → |
| Sedgwick County | 5B | 5B | Insulation → |
| Summit County | 7 | 7 | Insulation → |
| Teller County | 5B | 5B | Insulation → |
| Washington County | 5B | 5B | Insulation → |
| Weld County | 5B | 5B | Insulation → |
| Yuma County | 5B | 5B | 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 Colorado?
Colorado spans IECC climate zones 4B to 7; zone 5B is the most common. Find your county in the table above, or search by ZIP code.
How much attic insulation do I need in Colorado?
The 2021 IECC calls for R-60 in the attic everywhere in Colorado.
What energy code does Colorado use?
Colorado 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.
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