Climate zone 4A: mixed-humid
The mid-Atlantic and Ohio Valley belt: both a real heating season and a humid cooling season.
Zone 4A covers 717 counties in 18 states, home to about 68,360,477 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 4A
| Where | Guidance |
|---|---|
| Attic, uninsulated | R60 |
| Attic, 3–4 inches already | R49 |
| Floor over unheated space | R19 |
| 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 R10 insulative wall sheathing or an R13 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 4A counties fall in the mixed-humid Building America region. Real winters and humid summers: the house switches between heating and cooling twice a year, and freezes are short but real.
The “A” (moist) regime means humidity drives much of the care: drains, dehumidifying and keeping crawlspaces and basements dry.
Largest counties in zone 4A
States in this zone: Kentucky (120), Virginia (109), Missouri (87), Kansas (87), Tennessee (61), Indiana (45), Illinois (44), West Virginia (36), Ohio (24), Maryland (22), North Carolina (16), Oklahoma (15), Pennsylvania (14), New Jersey (13), Arkansas (12), New York (8), Delaware (3), District of Columbia (1).