IECC 2021 climate zone
Climate zone 8: subarctic
Interior and northern Alaska.
Zone 8 covers 7 counties in 1 state, home to about 137,645 people (FEMA NRI population). ENERGY STAR’s target for an uninsulated attic here is R60; with 3–4 inches already in place, add to R49.
Insulation targets for zone 8
| Where | Guidance |
|---|---|
| Attic, uninsulated | R60 |
| Attic, 3–4 inches already | R49 |
| Floor over unheated space | R38 |
| Walls | When siding is removed: blow insulation into empty cavities and add R5 to R10 insulative sheathing; on an insulated 2x4 wall, add R10 sheathing. |
| Basement or crawlspace walls | Add R15 insulative wall sheathing or an R19 batt. |
Homeowner retrofit guidance, not your local code. Your jurisdiction may enforce an older or amended IECC; ask the building department before a permit job.
What it means for upkeep
Most zone 8 counties fall in the subarctic Building America region. Extreme cold and long dark winters; heating reliability is a safety system.
Largest counties in zone 8
Fairbanks North Star Borough, AK95,579North Slope Borough, AK10,651Nome Census Area, AK10,031Northwest Arctic Borough, AK7,726Southeast Fairbanks Census Area, AK6,763Yukon-Koyukuk Census Area, AK5,280
States in this zone: Alaska (7).
PNNL county zone fileFEMA NRI population