Climate zones
Climate Zone 4
Climate zone 4 is the IECC's "mixed" zone. Under the 2021 map it covers 821 counties in 25 states plus Washington, DC, including New York City, St. Louis, Albuquerque, Seattle and Portland (4C). By moisture: 4A (humid) 721, 4B (dry) 66 and 4C (marine) 34. Zone 4 gets real heating and cooling seasons. Attics go up to R-60 and walls need either a thick cavity or foam board on the outside.
Insulation minimums in zone 4 (2021 IECC)
| Part of the house | 4A, 4B | 4C |
|---|---|---|
| Attic / ceiling | R-60 | R-60 |
| Wood-frame walls | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-30, or 20+5ci, or 13+10ci, or R-20ci |
| Mass walls (block, brick) | R-8 exterior / R-13 interior | R-13 exterior / R-17 interior |
| Floors over unheated space | R-19 | R-30 |
| Basement walls | R-10ci or R-13 | R-15ci, or R-19, or 13+5ci |
| Slab edge | R-10, 4 ft deep | R-10, 4 ft deep |
| Crawl space walls | R-10ci or R-13 | R-15ci, or R-19, or 13+5ci |
| Windows: max U-factor | U-0.30 | U-0.30 |
| Windows: max SHGC | 0.40 | 0.40 |
Marine zone 4C uses the zone 5 row of the code table, so its walls, floors and basements need more than 4A and 4B. "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 4
| State | Counties in zone 4 | Subzones |
|---|---|---|
| Kentucky | all 120 | 4A |
| Virginia | 111 of 136 | 4A |
| Kansas | 88 of 105 | 4A |
| Missouri | 87 of 115 | 4A |
| Tennessee | 61 of 95 | 4A |
| Indiana | 45 of 92 | 4A |
| Illinois | 44 of 102 | 4A |
| West Virginia | 36 of 55 | 4A |
| Texas | 28 of 254 | 4B |
| Ohio | 24 of 88 | 4A |
| Maryland | 22 of 24 | 4A |
| Oklahoma | 18 of 77 | 4A, 4B |
| Oregon | 18 of 36 | 4C |
| North Carolina | 16 of 100 | 4A |
| New Jersey | 14 of 21 | 4A |
| Pennsylvania | 14 of 67 | 4A |
| Washington | 14 of 39 | 4C |
| New Mexico | 13 of 33 | 4B |
| Arkansas | 12 of 75 | 4A |
| California | 10 of 58 | 4B, 4C |
| New York | 8 of 62 | 4A |
| Nevada | 7 of 17 | 4B |
| Colorado | 5 of 64 | 4B |
| Delaware | all 3 | 4A |
| Arizona | 2 of 15 | 4B |
| Washington, DC | all | 4A |
Every county in zone 4
Open a state to see its counties. The state pages list every county's zone, including the ones in other zones.
Kentucky (120)
- Adair County (4A)
- Allen County (4A)
- Anderson County (4A)
- Ballard County (4A)
- Barren County (4A)
- Bath County (4A)
- Bell County (4A)
- Boone County (4A)
- Bourbon County (4A)
- Boyd County (4A)
- Boyle County (4A)
- Bracken County (4A)
- Breathitt County (4A)
- Breckinridge County (4A)
- Bullitt County (4A)
- Butler County (4A)
- Caldwell County (4A)
- Calloway County (4A)
- Campbell County (4A)
- Carlisle County (4A)
- Carroll County (4A)
- Carter County (4A)
- Casey County (4A)
- Christian County (4A)
- Clark County (4A)
- Clay County (4A)
- Clinton County (4A)
- Crittenden County (4A)
- Cumberland County (4A)
- Daviess County (4A)
- Edmonson County (4A)
- Elliott County (4A)
- Estill County (4A)
- Fayette County (4A)
- Fleming County (4A)
- Floyd County (4A)
- Franklin County (4A)
- Fulton County (4A)
- Gallatin County (4A)
- Garrard County (4A)
- Grant County (4A)
- Graves County (4A)
- Grayson County (4A)
- Green County (4A)
- Greenup County (4A)
- Hancock County (4A)
- Hardin County (4A)
- Harlan County (4A)
- Harrison County (4A)
- Hart County (4A)
- Henderson County (4A)
- Henry County (4A)
- Hickman County (4A)
- Hopkins County (4A)
- Jackson County (4A)
- Jefferson County (4A)
- Jessamine County (4A)
- Johnson County (4A)
- Kenton County (4A)
- Knott County (4A)
- Knox County (4A)
- Larue County (4A)
- Laurel County (4A)
- Lawrence County (4A)
- Lee County (4A)
- Leslie County (4A)
- Letcher County (4A)
- Lewis County (4A)
- Lincoln County (4A)
- Livingston County (4A)
- Logan County (4A)
- Lyon County (4A)
- Madison County (4A)
- Magoffin County (4A)
- Marion County (4A)
- Marshall County (4A)
- Martin County (4A)
- Mason County (4A)
- McCracken County (4A)
- McCreary County (4A)
- McLean County (4A)
- Meade County (4A)
- Menifee County (4A)
- Mercer County (4A)
- Metcalfe County (4A)
- Monroe County (4A)
- Montgomery County (4A)
- Morgan County (4A)
- Muhlenberg County (4A)
- Nelson County (4A)
- Nicholas County (4A)
- Ohio County (4A)
- Oldham County (4A)
- Owen County (4A)
- Owsley County (4A)
- Pendleton County (4A)
- Perry County (4A)
- Pike County (4A)
- Powell County (4A)
- Pulaski County (4A)
- Robertson County (4A)
- Rockcastle County (4A)
- Rowan County (4A)
- Russell County (4A)
- Scott County (4A)
- Shelby County (4A)
- Simpson County (4A)
- Spencer County (4A)
- Taylor County (4A)
- Todd County (4A)
- Trigg County (4A)
- Trimble County (4A)
- Union County (4A)
- Warren County (4A)
- Washington County (4A)
- Wayne County (4A)
- Webster County (4A)
- Whitley County (4A)
- Wolfe County (4A)
- Woodford County (4A)
Virginia (111)
- Accomack County (4A)
- Albemarle County (4A)
- Alexandria (independent city) (4A)
- Amelia County (4A)
- Amherst County (4A)
- Appomattox County (4A)
- Arlington County (4A)
- Augusta County (4A)
- Bedford County (4A)
- Bedford (independent city) (4A)
- Bland County (4A)
- Botetourt County (4A)
- Bristol (independent city) (4A)
- Buchanan County (4A)
- Buckingham County (4A)
- Buena Vista (independent city) (4A)
- Campbell County (4A)
- Caroline County (4A)
- Carroll County (4A)
- Charles City County (4A)
- Charlotte County (4A)
- Charlottesville (independent city) (4A)
- Chesterfield County (4A)
- Clarke County (4A)
- Colonial Heights (independent city) (4A)
- Craig County (4A)
- Culpeper County (4A)
- Cumberland County (4A)
- Danville (independent city) (4A)
- Dickenson County (4A)
- Dinwiddie County (4A)
- Essex County (4A)
- Fairfax County (4A)
- Fairfax (independent city) (4A)
- Falls Church (independent city) (4A)
- Fauquier County (4A)
- Floyd County (4A)
- Fluvanna County (4A)
- Frederick County (4A)
- Fredericksburg (independent city) (4A)
- Galax (independent city) (4A)
- Giles County (4A)
- Gloucester County (4A)
- Goochland County (4A)
- Grayson County (4A)
- Greene County (4A)
- Hanover County (4A)
- Harrisonburg (independent city) (4A)
- Henrico County (4A)
- Henry County (4A)
- Hopewell (independent city) (4A)
- James City County (4A)
- King and Queen County (4A)
- King George County (4A)
- King William County (4A)
- Lancaster County (4A)
- Lee County (4A)
- Lexington (independent city) (4A)
- Loudoun County (4A)
- Louisa County (4A)
- Lunenburg County (4A)
- Lynchburg (independent city) (4A)
- Madison County (4A)
- Manassas (independent city) (4A)
- Manassas Park (independent city) (4A)
- Martinsville (independent city) (4A)
- Mathews County (4A)
- Middlesex County (4A)
- Montgomery County (4A)
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- Norton (independent city) (4A)
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Kansas (88)
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- Chase County (4A)
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- Clark County (4A)
- Clay County (4A)
- Cloud County (4A)
- Coffey County (4A)
- Comanche County (4A)
- Cowley County (4A)
- Crawford County (4A)
- Dickinson County (4A)
- Doniphan County (4A)
- Douglas County (4A)
- Edwards County (4A)
- Elk County (4A)
- Ellis County (4A)
- Ellsworth County (4A)
- Finney County (4A)
- Ford County (4A)
- Franklin County (4A)
- Geary County (4A)
- Graham County (4A)
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- Gray County (4A)
- Greenwood County (4A)
- Hamilton County (4A)
- Harper County (4A)
- Harvey County (4A)
- Haskell County (4A)
- Hodgeman County (4A)
- Jackson County (4A)
- Jefferson County (4A)
- Johnson County (4A)
- Kearny County (4A)
- Kingman County (4A)
- Kiowa County (4A)
- Labette County (4A)
- Lane County (4A)
- Leavenworth County (4A)
- Lincoln County (4A)
- Linn County (4A)
- Lyon County (4A)
- Marion County (4A)
- Marshall County (4A)
- McPherson County (4A)
- Meade County (4A)
- Miami County (4A)
- Mitchell County (4A)
- Montgomery County (4A)
- Morris County (4A)
- Morton County (4A)
- Nemaha County (4A)
- Neosho County (4A)
- Ness County (4A)
- Osage County (4A)
- Osborne County (4A)
- Ottawa County (4A)
- Pawnee County (4A)
- Pottawatomie County (4A)
- Pratt County (4A)
- Reno County (4A)
- Rice County (4A)
- Riley County (4A)
- Rooks County (4A)
- Rush County (4A)
- Russell County (4A)
- Saline County (4A)
- Sedgwick County (4A)
- Seward County (4A)
- Shawnee County (4A)
- Stafford County (4A)
- Stanton County (4A)
- Stevens County (4A)
- Sumner County (4A)
- Trego County (4A)
- Wabaunsee County (4A)
- Washington County (4A)
- Wilson County (4A)
- Woodson County (4A)
- Wyandotte County (4A)
Missouri (87)
- Audrain County (4A)
- Barry County (4A)
- Barton County (4A)
- Bates County (4A)
- Benton County (4A)
- Bollinger County (4A)
- Boone County (4A)
- Buchanan County (4A)
- Butler County (4A)
- Caldwell County (4A)
- Callaway County (4A)
- Camden County (4A)
- Cape Girardeau County (4A)
- Carroll County (4A)
- Carter County (4A)
- Cass County (4A)
- Cedar County (4A)
- Chariton County (4A)
- Christian County (4A)
- Clay County (4A)
- Clinton County (4A)
- Cole County (4A)
- Cooper County (4A)
- Crawford County (4A)
- Dade County (4A)
- Dallas County (4A)
- Dent County (4A)
- Douglas County (4A)
- Franklin County (4A)
- Gasconade County (4A)
- Greene County (4A)
- Henry County (4A)
- Hickory County (4A)
- Howard County (4A)
- Howell County (4A)
- Iron County (4A)
- Jackson County (4A)
- Jasper County (4A)
- Jefferson County (4A)
- Johnson County (4A)
- Laclede County (4A)
- Lafayette County (4A)
- Lawrence County (4A)
- Lincoln County (4A)
- Madison County (4A)
- Maries County (4A)
- McDonald County (4A)
- Miller County (4A)
- Mississippi County (4A)
- Moniteau County (4A)
- Monroe County (4A)
- Montgomery County (4A)
- Morgan County (4A)
- New Madrid County (4A)
- Newton County (4A)
- Oregon County (4A)
- Osage County (4A)
- Ozark County (4A)
- Perry County (4A)
- Pettis County (4A)
- Phelps County (4A)
- Platte County (4A)
- Polk County (4A)
- Pulaski County (4A)
- Randolph County (4A)
- Ray County (4A)
- Reynolds County (4A)
- Ripley County (4A)
- Saline County (4A)
- Scott County (4A)
- Shannon County (4A)
- St. Charles County (4A)
- St. Clair County (4A)
- St. Francois County (4A)
- St. Louis County (4A)
- St. Louis (independent city) (4A)
- Ste. Genevieve County (4A)
- Stoddard County (4A)
- Stone County (4A)
- Taney County (4A)
- Texas County (4A)
- Vernon County (4A)
- Warren County (4A)
- Washington County (4A)
- Wayne County (4A)
- Webster County (4A)
- Wright County (4A)
Tennessee (61)
- Anderson County (4A)
- Benton County (4A)
- Bledsoe County (4A)
- Blount County (4A)
- Bradley County (4A)
- Campbell County (4A)
- Cannon County (4A)
- Carroll County (4A)
- Carter County (4A)
- Cheatham County (4A)
- Claiborne County (4A)
- Clay County (4A)
- Cocke County (4A)
- Cumberland County (4A)
- DeKalb County (4A)
- Dickson County (4A)
- Fentress County (4A)
- Grainger County (4A)
- Greene County (4A)
- Hamblen County (4A)
- Hancock County (4A)
- Hawkins County (4A)
- Henry County (4A)
- Houston County (4A)
- Humphreys County (4A)
- Jackson County (4A)
- Jefferson County (4A)
- Johnson County (4A)
- Knox County (4A)
- Lake County (4A)
- Loudon County (4A)
- Macon County (4A)
- McMinn County (4A)
- Meigs County (4A)
- Monroe County (4A)
- Montgomery County (4A)
- Morgan County (4A)
- Obion County (4A)
- Overton County (4A)
- Pickett County (4A)
- Polk County (4A)
- Putnam County (4A)
- Rhea County (4A)
- Roane County (4A)
- Robertson County (4A)
- Scott County (4A)
- Sequatchie County (4A)
- Sevier County (4A)
- Smith County (4A)
- Stewart County (4A)
- Sullivan County (4A)
- Sumner County (4A)
- Trousdale County (4A)
- Unicoi County (4A)
- Union County (4A)
- Van Buren County (4A)
- Warren County (4A)
- Washington County (4A)
- Weakley County (4A)
- White County (4A)
- Wilson County (4A)
Indiana (45)
- Bartholomew County (4A)
- Brown County (4A)
- Clark County (4A)
- Clay County (4A)
- Crawford County (4A)
- Daviess County (4A)
- Dearborn County (4A)
- Decatur County (4A)
- Dubois County (4A)
- Fayette County (4A)
- Floyd County (4A)
- Franklin County (4A)
- Gibson County (4A)
- Greene County (4A)
- Harrison County (4A)
- Hendricks County (4A)
- Jackson County (4A)
- Jefferson County (4A)
- Jennings County (4A)
- Johnson County (4A)
- Knox County (4A)
- Lawrence County (4A)
- Marion County (4A)
- Martin County (4A)
- Monroe County (4A)
- Morgan County (4A)
- Ohio County (4A)
- Orange County (4A)
- Owen County (4A)
- Perry County (4A)
- Pike County (4A)
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- Putnam County (4A)
- Ripley County (4A)
- Rush County (4A)
- Scott County (4A)
- Shelby County (4A)
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Illinois (44)
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- Franklin County (4A)
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- Greene County (4A)
- Hamilton County (4A)
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West Virginia (36)
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Texas (28)
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Ohio (24)
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Maryland (22)
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Oklahoma (18)
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Oregon (18)
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North Carolina (16)
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New Jersey (14)
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- Hudson County (4A)
- Mercer County (4A)
- Middlesex County (4A)
- Monmouth County (4A)
- Ocean County (4A)
- Salem County (4A)
- Union County (4A)
Pennsylvania (14)
- Adams County (4A)
- Berks County (4A)
- Bucks County (4A)
- Chester County (4A)
- Cumberland County (4A)
- Dauphin County (4A)
- Delaware County (4A)
- Franklin County (4A)
- Lancaster County (4A)
- Lebanon County (4A)
- Montgomery County (4A)
- Perry County (4A)
- Philadelphia County (4A)
- York County (4A)
Washington (14)
- Clark County (4C)
- Cowlitz County (4C)
- Grays Harbor County (4C)
- Jefferson County (4C)
- King County (4C)
- Lewis County (4C)
- Mason County (4C)
- Pacific County (4C)
- Pierce County (4C)
- Skagit County (4C)
- Snohomish County (4C)
- Thurston County (4C)
- Wahkiakum County (4C)
- Whatcom County (4C)
New Mexico (13)
- Bernalillo County (4B)
- Catron County (4B)
- Cibola County (4B)
- Curry County (4B)
- DeBaca County (4B)
- Grant County (4B)
- Guadalupe County (4B)
- Lincoln County (4B)
- Quay County (4B)
- Roosevelt County (4B)
- Socorro County (4B)
- Union County (4B)
- Valencia County (4B)
Arkansas (12)
- Baxter County (4A)
- Benton County (4A)
- Boone County (4A)
- Carroll County (4A)
- Fulton County (4A)
- Izard County (4A)
- Madison County (4A)
- Marion County (4A)
- Newton County (4A)
- Searcy County (4A)
- Stone County (4A)
- Washington County (4A)
California (10)
- Amador County (4B)
- Calaveras County (4B)
- Del Norte County (4C)
- El Dorado County (4B)
- Humboldt County (4C)
- Inyo County (4B)
- Lake County (4B)
- Mariposa County (4B)
- Trinity County (4B)
- Tuolumne County (4B)
New York (8)
- Bronx County (4A)
- Kings County (4A)
- Nassau County (4A)
- New York County (4A)
- Queens County (4A)
- Richmond County (4A)
- Suffolk County (4A)
- Westchester County (4A)
Nevada (7)
- Carson City (independent city) (4B)
- Douglas County (4B)
- Esmeralda County (4B)
- Lincoln County (4B)
- Lyon County (4B)
- Mineral County (4B)
- Nye County (4B)
Colorado (5)
- Baca County (4B)
- Bent County (4B)
- Las Animas County (4B)
- Otero County (4B)
- Prowers County (4B)
Delaware (3)
- Kent County (4A)
- New Castle County (4A)
- Sussex County (4A)
Arizona (2)
- Gila County (4B)
- Yavapai County (4B)
Washington, DC (1)
- District of Columbia (4A)
What changed in the 2021 map
95 of these counties were in a different zone under the 2018 map: 79 moved here from a colder zone and 16 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 4?
One of the eight US climate zones in the International Energy Conservation Code (IECC). Zone 4 gets real heating and cooling seasons. Attics go up to R-60 and walls need either a thick cavity or foam board on the outside. It covers 821 counties in 25 states plus Washington, DC.
How much attic insulation do I need in climate zone 4?
In zone 4, 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 4?
Kentucky, Virginia, Kansas, Missouri, Tennessee, Indiana, Illinois, West Virginia, Texas, Ohio, Maryland, Oklahoma, Oregon, North Carolina, New Jersey, Pennsylvania, Washington, New Mexico, Arkansas, California, New York, Nevada, Colorado, Delaware, Arizona and Washington, DC. Kentucky and Delaware are entirely in zone 4.
What do the letters A, B and C mean?
They describe moisture: 4A is humid, 4B is dry and 4C is marine (the mild, damp Pacific coast). Here the letter matters: 4A and 4B share the same minimums; 4C uses the stricter zone 5 row, as the table above shows.
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.