Climate zone 6A: cold-humid
The upper Midwest and northern New England: long heating seasons.
Zone 6A covers 306 counties in 11 states, home to about 13,191,963 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 6A
| Where | Guidance |
|---|---|
| Attic, uninsulated | R60 |
| Attic, 3–4 inches already | R49 |
| Floor over unheated space | R30 |
| 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 6A counties fall in the cold Building America region. Heating season dominates. Freeze protection, ice dams and furnace care are the big-ticket risks.
The “A” (moist) regime means humidity drives much of the care: drains, dehumidifying and keeping crawlspaces and basements dry.
Largest counties in zone 6A
States in this zone: Minnesota (61), South Dakota (48), Michigan (44), Wisconsin (42), North Dakota (37), New York (18), Maine (15), Iowa (15), Vermont (14), Alaska (7), New Hampshire (5).