Climate Zone 7
Climate zone 7 is the IECC's "very cold" zone. Under the 2021 map it covers 69 counties in 7 states, including Duluth, Anchorage and Jackson WY. Zone 7 has long, severe winters. Floors over unheated space need R-38, the most of any zone.
Insulation minimums in zone 7 (2021 IECC)
| Part of the house | 7 |
|---|---|
| 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 7
| State | Counties in zone 7 |
|---|---|
| Minnesota | 23 of 87 |
| North Dakota | 16 of 53 |
| Colorado | 13 of 64 |
| Alaska | 11 of 27 |
| Wyoming | 3 of 23 |
| Michigan | 2 of 83 |
| Maine | 1 of 16 |
Every county in zone 7
Open a state to see its counties. The state pages list every county's zone, including the ones in other zones.
Minnesota (23)
- Aitkin County
- Beltrami County
- Carlton County
- Cass County
- Clearwater County
- Cook County
- Crow Wing County
- Hubbard County
- Itasca County
- Kittson County
- Koochiching County
- Lake County
- Lake of the Woods County
- Mahnomen County
- Marshall County
- Norman County
- Pennington County
- Pine County
- Polk County
- Red Lake County
- Roseau County
- St. Louis County
- Wadena County
North Dakota (16)
- Benson County
- Bottineau County
- Burke County
- Cavalier County
- Divide County
- Grand Forks County
- McHenry County
- Nelson County
- Pembina County
- Pierce County
- Ramsey County
- Renville County
- Rolette County
- Towner County
- Walsh County
- Ward County
Colorado (13)
- Clear Creek County
- Grand County
- Gunnison County
- Hinsdale County
- Jackson County
- Lake County
- Mineral County
- Park County
- Pitkin County
- Rio Grande County
- Routt County
- San Juan County
- Summit County
Alaska (11)
- Aleutians East
- Aleutians West Census Area
- Anchorage
- Bethel Census Area
- Bristol Bay
- Dillingham Census Area
- Kenai Peninsula
- Lake and Peninsula
- Matanuska-Susitna
- Valdez-Cordova Census Area
- Yakutat
Wyoming (3)
- Lincoln County
- Sublette County
- Teton County
Michigan (2)
- Keweenaw County
- Marquette County
Maine (1)
- Aroostook County
What changed in the 2021 map
3 of these counties were in a different zone under the 2018 map: 2 moved here from a colder zone and 1 from a warmer one. 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 7?
One of the eight US climate zones in the International Energy Conservation Code (IECC). Zone 7 has long, severe winters. Floors over unheated space need R-38, the most of any zone. It covers 69 counties in 7 states.
How much attic insulation do I need in climate zone 7?
In zone 7, 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 7?
Minnesota, North Dakota, Colorado, Alaska, Wyoming, Michigan and Maine.
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.