Climate zones
Climate Zone 3
Climate zone 3 is the IECC's "warm" zone. Under the 2021 map it covers 762 counties in 17 states, including Plano (Collin County), Atlanta, Las Vegas and Los Angeles. By moisture: 3A (humid) 638, 3B (dry) 110 and 3C (marine) 14. Zone 3 has hot summers and mild winters. The code asks for an R-49 attic, R-20 walls (or R-13 plus R-5 foam) and R-10 foam along the slab edge, 2 ft deep.
Insulation minimums in zone 3 (2021 IECC)
| Part of the house | 3A, 3B, 3C |
|---|---|
| Attic / ceiling | R-49 |
| Wood-frame walls | R-20, or 13+5ci, or R-15ci |
| Mass walls (block, brick) | R-8 exterior / R-13 interior |
| Floors over unheated space | R-19 |
| Basement walls | R-5ci or R-13 |
| Slab edge | R-10, 2 ft deep |
| Crawl space walls | R-5ci or R-13 |
| Windows: max U-factor | U-0.30 |
| Windows: max SHGC | 0.25 |
"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-49 in an uninsulated attic, or adding R-38 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 3
| State | Counties in zone 3 | Subzones |
|---|---|---|
| Texas | 128 of 254 | 3A, 3B |
| Georgia | 118 of 159 | 3A |
| North Carolina | 79 of 100 | 3A |
| Mississippi | 76 of 82 | 3A |
| Arkansas | 63 of 75 | 3A |
| Oklahoma | 59 of 77 | 3A |
| Alabama | 58 of 67 | 3A |
| South Carolina | 44 of 46 | 3A |
| California | 39 of 58 | 3B, 3C |
| Tennessee | 34 of 95 | 3A |
| Louisiana | 27 of 64 | 3A |
| Virginia | 20 of 136 | 3A |
| New Mexico | 8 of 33 | 3B |
| Arizona | 5 of 15 | 3B |
| Missouri | 2 of 115 | 3A |
| Nevada | 1 of 17 | 3B |
| Utah | 1 of 29 | 3B |
Every county in zone 3
Open a state to see its counties. The state pages list every county's zone, including the ones in other zones.
Texas (128)
- Andrews County (3B)
- Archer County (3A)
- Baylor County (3B)
- Blanco County (3A)
- Borden County (3B)
- Bowie County (3A)
- Brewster County (3B)
- Brown County (3A)
- Burnet County (3A)
- Callahan County (3B)
- Camp County (3A)
- Cass County (3A)
- Childress County (3B)
- Clay County (3A)
- Coke County (3B)
- Coleman County (3B)
- Collin County (3A)
- Collingsworth County (3B)
- Comanche County (3A)
- Concho County (3B)
- Cooke County (3A)
- Cottle County (3B)
- Crane County (3B)
- Crockett County (3B)
- Crosby County (3B)
- Culberson County (3B)
- Dawson County (3B)
- Delta County (3A)
- Denton County (3A)
- Dickens County (3B)
- Eastland County (3A)
- Ector County (3B)
- El Paso County (3B)
- Erath County (3A)
- Fannin County (3A)
- Fisher County (3B)
- Foard County (3B)
- Franklin County (3A)
- Gaines County (3B)
- Garza County (3B)
- Gillespie County (3A)
- Glasscock County (3B)
- Grayson County (3A)
- Gregg County (3A)
- Hall County (3B)
- Hamilton County (3A)
- Hardeman County (3B)
- Harrison County (3A)
- Haskell County (3B)
- Hemphill County (3B)
- Henderson County (3A)
- Hood County (3A)
- Hopkins County (3A)
- Howard County (3B)
- Hudspeth County (3B)
- Hunt County (3A)
- Irion County (3B)
- Jack County (3A)
- Jeff Davis County (3B)
- Jones County (3B)
- Kaufman County (3A)
- Kendall County (3A)
- Kent County (3B)
- Kerr County (3B)
- Kimble County (3B)
- King County (3B)
- Knox County (3B)
- Lamar County (3A)
- Lampasas County (3A)
- Llano County (3A)
- Loving County (3B)
- Lubbock County (3B)
- Lynn County (3B)
- Marion County (3A)
- Martin County (3B)
- Mason County (3B)
- McCulloch County (3B)
- Menard County (3B)
- Midland County (3B)
- Mills County (3A)
- Mitchell County (3B)
- Montague County (3A)
- Morris County (3A)
- Motley County (3B)
- Nacogdoches County (3A)
- Nolan County (3B)
- Palo Pinto County (3A)
- Panola County (3A)
- Parker County (3A)
- Pecos County (3B)
- Presidio County (3B)
- Rains County (3A)
- Reagan County (3B)
- Red River County (3A)
- Reeves County (3B)
- Rockwall County (3A)
- Runnels County (3B)
- Rusk County (3A)
- Sabine County (3A)
- San Augustine County (3A)
- San Saba County (3A)
- Schleicher County (3B)
- Scurry County (3B)
- Shackelford County (3B)
- Shelby County (3A)
- Smith County (3A)
- Somervell County (3A)
- Stephens County (3A)
- Sterling County (3B)
- Stonewall County (3B)
- Sutton County (3B)
- Taylor County (3B)
- Terrell County (3B)
- Terry County (3B)
- Throckmorton County (3B)
- Titus County (3A)
- Tom Green County (3B)
- Upshur County (3A)
- Upton County (3B)
- Van Zandt County (3A)
- Ward County (3B)
- Wheeler County (3B)
- Wichita County (3A)
- Wilbarger County (3B)
- Winkler County (3B)
- Wise County (3A)
- Wood County (3A)
- Young County (3A)
Georgia (118)
- Baldwin County (3A)
- Banks County (3A)
- Barrow County (3A)
- Bartow County (3A)
- Ben Hill County (3A)
- Bibb County (3A)
- Bleckley County (3A)
- Bulloch County (3A)
- Burke County (3A)
- Butts County (3A)
- Candler County (3A)
- Carroll County (3A)
- Catoosa County (3A)
- Chattahoochee County (3A)
- Chattooga County (3A)
- Cherokee County (3A)
- Clarke County (3A)
- Clay County (3A)
- Clayton County (3A)
- Cobb County (3A)
- Columbia County (3A)
- Coweta County (3A)
- Crawford County (3A)
- Crisp County (3A)
- Dade County (3A)
- Dawson County (3A)
- DeKalb County (3A)
- Dodge County (3A)
- Dooly County (3A)
- Douglas County (3A)
- Elbert County (3A)
- Emanuel County (3A)
- Fannin County (3A)
- Fayette County (3A)
- Floyd County (3A)
- Forsyth County (3A)
- Franklin County (3A)
- Fulton County (3A)
- Gilmer County (3A)
- Glascock County (3A)
- Gordon County (3A)
- Greene County (3A)
- Gwinnett County (3A)
- Habersham County (3A)
- Hall County (3A)
- Hancock County (3A)
- Haralson County (3A)
- Harris County (3A)
- Hart County (3A)
- Heard County (3A)
- Henry County (3A)
- Houston County (3A)
- Irwin County (3A)
- Jackson County (3A)
- Jasper County (3A)
- Jefferson County (3A)
- Jenkins County (3A)
- Johnson County (3A)
- Jones County (3A)
- Lamar County (3A)
- Laurens County (3A)
- Lee County (3A)
- Lincoln County (3A)
- Lumpkin County (3A)
- Macon County (3A)
- Madison County (3A)
- Marion County (3A)
- McDuffie County (3A)
- Meriwether County (3A)
- Monroe County (3A)
- Montgomery County (3A)
- Morgan County (3A)
- Murray County (3A)
- Muscogee County (3A)
- Newton County (3A)
- Oconee County (3A)
- Oglethorpe County (3A)
- Paulding County (3A)
- Peach County (3A)
- Pickens County (3A)
- Pike County (3A)
- Polk County (3A)
- Pulaski County (3A)
- Putnam County (3A)
- Quitman County (3A)
- Rabun County (3A)
- Randolph County (3A)
- Richmond County (3A)
- Rockdale County (3A)
- Schley County (3A)
- Screven County (3A)
- Spalding County (3A)
- Stephens County (3A)
- Stewart County (3A)
- Sumter County (3A)
- Talbot County (3A)
- Taliaferro County (3A)
- Taylor County (3A)
- Telfair County (3A)
- Terrell County (3A)
- Towns County (3A)
- Treutlen County (3A)
- Troup County (3A)
- Turner County (3A)
- Twiggs County (3A)
- Union County (3A)
- Upson County (3A)
- Walker County (3A)
- Walton County (3A)
- Warren County (3A)
- Washington County (3A)
- Webster County (3A)
- Wheeler County (3A)
- White County (3A)
- Whitfield County (3A)
- Wilcox County (3A)
- Wilkes County (3A)
- Wilkinson County (3A)
North Carolina (79)
- Alamance County (3A)
- Alexander County (3A)
- Anson County (3A)
- Beaufort County (3A)
- Bertie County (3A)
- Bladen County (3A)
- Brunswick County (3A)
- Cabarrus County (3A)
- Camden County (3A)
- Carteret County (3A)
- Caswell County (3A)
- Catawba County (3A)
- Chatham County (3A)
- Cherokee County (3A)
- Chowan County (3A)
- Clay County (3A)
- Cleveland County (3A)
- Columbus County (3A)
- Craven County (3A)
- Cumberland County (3A)
- Currituck County (3A)
- Dare County (3A)
- Davidson County (3A)
- Davie County (3A)
- Duplin County (3A)
- Durham County (3A)
- Edgecombe County (3A)
- Forsyth County (3A)
- Franklin County (3A)
- Gaston County (3A)
- Gates County (3A)
- Granville County (3A)
- Greene County (3A)
- Guilford County (3A)
- Halifax County (3A)
- Harnett County (3A)
- Hertford County (3A)
- Hoke County (3A)
- Hyde County (3A)
- Iredell County (3A)
- Johnston County (3A)
- Jones County (3A)
- Lee County (3A)
- Lenoir County (3A)
- Lincoln County (3A)
- Martin County (3A)
- Mecklenburg County (3A)
- Montgomery County (3A)
- Moore County (3A)
- Nash County (3A)
- New Hanover County (3A)
- Northampton County (3A)
- Onslow County (3A)
- Orange County (3A)
- Pamlico County (3A)
- Pasquotank County (3A)
- Pender County (3A)
- Perquimans County (3A)
- Person County (3A)
- Pitt County (3A)
- Polk County (3A)
- Randolph County (3A)
- Richmond County (3A)
- Robeson County (3A)
- Rockingham County (3A)
- Rowan County (3A)
- Rutherford County (3A)
- Sampson County (3A)
- Scotland County (3A)
- Stanly County (3A)
- Tyrrell County (3A)
- Union County (3A)
- Vance County (3A)
- Wake County (3A)
- Warren County (3A)
- Washington County (3A)
- Wayne County (3A)
- Wilkes County (3A)
- Wilson County (3A)
Mississippi (76)
- Adams County (3A)
- Alcorn County (3A)
- Amite County (3A)
- Attala County (3A)
- Benton County (3A)
- Bolivar County (3A)
- Calhoun County (3A)
- Carroll County (3A)
- Chickasaw County (3A)
- Choctaw County (3A)
- Claiborne County (3A)
- Clarke County (3A)
- Clay County (3A)
- Coahoma County (3A)
- Copiah County (3A)
- Covington County (3A)
- DeSoto County (3A)
- Forrest County (3A)
- Franklin County (3A)
- Greene County (3A)
- Grenada County (3A)
- Hinds County (3A)
- Holmes County (3A)
- Humphreys County (3A)
- Issaquena County (3A)
- Itawamba County (3A)
- Jasper County (3A)
- Jefferson County (3A)
- Jefferson Davis County (3A)
- Jones County (3A)
- Kemper County (3A)
- Lafayette County (3A)
- Lamar County (3A)
- Lauderdale County (3A)
- Lawrence County (3A)
- Leake County (3A)
- Lee County (3A)
- Leflore County (3A)
- Lincoln County (3A)
- Lowndes County (3A)
- Madison County (3A)
- Marion County (3A)
- Marshall County (3A)
- Monroe County (3A)
- Montgomery County (3A)
- Neshoba County (3A)
- Newton County (3A)
- Noxubee County (3A)
- Oktibbeha County (3A)
- Panola County (3A)
- Perry County (3A)
- Pike County (3A)
- Pontotoc County (3A)
- Prentiss County (3A)
- Quitman County (3A)
- Rankin County (3A)
- Scott County (3A)
- Sharkey County (3A)
- Simpson County (3A)
- Smith County (3A)
- Sunflower County (3A)
- Tallahatchie County (3A)
- Tate County (3A)
- Tippah County (3A)
- Tishomingo County (3A)
- Tunica County (3A)
- Union County (3A)
- Walthall County (3A)
- Warren County (3A)
- Washington County (3A)
- Wayne County (3A)
- Webster County (3A)
- Wilkinson County (3A)
- Winston County (3A)
- Yalobusha County (3A)
- Yazoo County (3A)
Arkansas (63)
- Arkansas County (3A)
- Ashley County (3A)
- Bradley County (3A)
- Calhoun County (3A)
- Chicot County (3A)
- Clark County (3A)
- Clay County (3A)
- Cleburne County (3A)
- Cleveland County (3A)
- Columbia County (3A)
- Conway County (3A)
- Craighead County (3A)
- Crawford County (3A)
- Crittenden County (3A)
- Cross County (3A)
- Dallas County (3A)
- Desha County (3A)
- Drew County (3A)
- Faulkner County (3A)
- Franklin County (3A)
- Garland County (3A)
- Grant County (3A)
- Greene County (3A)
- Hempstead County (3A)
- Hot Spring County (3A)
- Howard County (3A)
- Independence County (3A)
- Jackson County (3A)
- Jefferson County (3A)
- Johnson County (3A)
- Lafayette County (3A)
- Lawrence County (3A)
- Lee County (3A)
- Lincoln County (3A)
- Little River County (3A)
- Logan County (3A)
- Lonoke County (3A)
- Miller County (3A)
- Mississippi County (3A)
- Monroe County (3A)
- Montgomery County (3A)
- Nevada County (3A)
- Ouachita County (3A)
- Perry County (3A)
- Phillips County (3A)
- Pike County (3A)
- Poinsett County (3A)
- Polk County (3A)
- Pope County (3A)
- Prairie County (3A)
- Pulaski County (3A)
- Randolph County (3A)
- Saline County (3A)
- Scott County (3A)
- Sebastian County (3A)
- Sevier County (3A)
- Sharp County (3A)
- St. Francis County (3A)
- Union County (3A)
- Van Buren County (3A)
- White County (3A)
- Woodruff County (3A)
- Yell County (3A)
Oklahoma (59)
- Adair County (3A)
- Atoka County (3A)
- Beckham County (3A)
- Blaine County (3A)
- Bryan County (3A)
- Caddo County (3A)
- Canadian County (3A)
- Carter County (3A)
- Cherokee County (3A)
- Choctaw County (3A)
- Cleveland County (3A)
- Coal County (3A)
- Comanche County (3A)
- Cotton County (3A)
- Creek County (3A)
- Custer County (3A)
- Dewey County (3A)
- Garvin County (3A)
- Grady County (3A)
- Greer County (3A)
- Harmon County (3A)
- Haskell County (3A)
- Hughes County (3A)
- Jackson County (3A)
- Jefferson County (3A)
- Johnston County (3A)
- Kingfisher County (3A)
- Kiowa County (3A)
- Latimer County (3A)
- Le Flore County (3A)
- Lincoln County (3A)
- Logan County (3A)
- Love County (3A)
- Marshall County (3A)
- Mayes County (3A)
- McClain County (3A)
- McCurtain County (3A)
- McIntosh County (3A)
- Murray County (3A)
- Muskogee County (3A)
- Noble County (3A)
- Okfuskee County (3A)
- Oklahoma County (3A)
- Okmulgee County (3A)
- Pawnee County (3A)
- Payne County (3A)
- Pittsburg County (3A)
- Pontotoc County (3A)
- Pottawatomie County (3A)
- Pushmataha County (3A)
- Roger Mills County (3A)
- Rogers County (3A)
- Seminole County (3A)
- Sequoyah County (3A)
- Stephens County (3A)
- Tillman County (3A)
- Tulsa County (3A)
- Wagoner County (3A)
- Washita County (3A)
Alabama (58)
- Autauga County (3A)
- Barbour County (3A)
- Bibb County (3A)
- Blount County (3A)
- Bullock County (3A)
- Butler County (3A)
- Calhoun County (3A)
- Chambers County (3A)
- Cherokee County (3A)
- Chilton County (3A)
- Choctaw County (3A)
- Clarke County (3A)
- Clay County (3A)
- Cleburne County (3A)
- Colbert County (3A)
- Conecuh County (3A)
- Coosa County (3A)
- Crenshaw County (3A)
- Cullman County (3A)
- Dallas County (3A)
- DeKalb County (3A)
- Elmore County (3A)
- Etowah County (3A)
- Fayette County (3A)
- Franklin County (3A)
- Greene County (3A)
- Hale County (3A)
- Jackson County (3A)
- Jefferson County (3A)
- Lamar County (3A)
- Lauderdale County (3A)
- Lawrence County (3A)
- Lee County (3A)
- Limestone County (3A)
- Lowndes County (3A)
- Macon County (3A)
- Madison County (3A)
- Marengo County (3A)
- Marion County (3A)
- Marshall County (3A)
- Monroe County (3A)
- Montgomery County (3A)
- Morgan County (3A)
- Perry County (3A)
- Pickens County (3A)
- Pike County (3A)
- Randolph County (3A)
- Russell County (3A)
- Shelby County (3A)
- St. Clair County (3A)
- Sumter County (3A)
- Talladega County (3A)
- Tallapoosa County (3A)
- Tuscaloosa County (3A)
- Walker County (3A)
- Washington County (3A)
- Wilcox County (3A)
- Winston County (3A)
South Carolina (44)
- Abbeville County (3A)
- Aiken County (3A)
- Allendale County (3A)
- Anderson County (3A)
- Bamberg County (3A)
- Barnwell County (3A)
- Berkeley County (3A)
- Calhoun County (3A)
- Charleston County (3A)
- Cherokee County (3A)
- Chester County (3A)
- Chesterfield County (3A)
- Clarendon County (3A)
- Colleton County (3A)
- Darlington County (3A)
- Dillon County (3A)
- Dorchester County (3A)
- Edgefield County (3A)
- Fairfield County (3A)
- Florence County (3A)
- Georgetown County (3A)
- Greenville County (3A)
- Greenwood County (3A)
- Hampton County (3A)
- Horry County (3A)
- Kershaw County (3A)
- Lancaster County (3A)
- Laurens County (3A)
- Lee County (3A)
- Lexington County (3A)
- Marion County (3A)
- Marlboro County (3A)
- McCormick County (3A)
- Newberry County (3A)
- Oconee County (3A)
- Orangeburg County (3A)
- Pickens County (3A)
- Richland County (3A)
- Saluda County (3A)
- Spartanburg County (3A)
- Sumter County (3A)
- Union County (3A)
- Williamsburg County (3A)
- York County (3A)
California (39)
- Alameda County (3C)
- Butte County (3B)
- Colusa County (3B)
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- Shasta County (3B)
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- Sutter County (3B)
- Tehama County (3B)
- Tulare County (3B)
- Ventura County (3C)
- Yolo County (3B)
- Yuba County (3B)
Tennessee (34)
- Bedford County (3A)
- Chester County (3A)
- Coffee County (3A)
- Crockett County (3A)
- Davidson County (3A)
- Decatur County (3A)
- Dyer County (3A)
- Fayette County (3A)
- Franklin County (3A)
- Gibson County (3A)
- Giles County (3A)
- Grundy County (3A)
- Hamilton County (3A)
- Hardeman County (3A)
- Hardin County (3A)
- Haywood County (3A)
- Henderson County (3A)
- Hickman County (3A)
- Lauderdale County (3A)
- Lawrence County (3A)
- Lewis County (3A)
- Lincoln County (3A)
- Madison County (3A)
- Marion County (3A)
- Marshall County (3A)
- Maury County (3A)
- McNairy County (3A)
- Moore County (3A)
- Perry County (3A)
- Rutherford County (3A)
- Shelby County (3A)
- Tipton County (3A)
- Wayne County (3A)
- Williamson County (3A)
Louisiana (27)
- Bienville Parish (3A)
- Bossier Parish (3A)
- Caddo Parish (3A)
- Caldwell Parish (3A)
- Catahoula Parish (3A)
- Claiborne Parish (3A)
- Concordia Parish (3A)
- De Soto Parish (3A)
- East Carroll Parish (3A)
- Franklin Parish (3A)
- Grant Parish (3A)
- Jackson Parish (3A)
- La Salle Parish (3A)
- Lincoln Parish (3A)
- Madison Parish (3A)
- Morehouse Parish (3A)
- Natchitoches Parish (3A)
- Ouachita Parish (3A)
- Red River Parish (3A)
- Richland Parish (3A)
- Sabine Parish (3A)
- Tensas Parish (3A)
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- Vernon Parish (3A)
- Webster Parish (3A)
- West Carroll Parish (3A)
- Winn Parish (3A)
Virginia (20)
- Brunswick County (3A)
- Chesapeake (independent city) (3A)
- Emporia (independent city) (3A)
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- Virginia Beach (independent city) (3A)
New Mexico (8)
- Chaves County (3B)
- Dona Ana County (3B)
- Eddy County (3B)
- Hidalgo County (3B)
- Lea County (3B)
- Luna County (3B)
- Otero County (3B)
- Sierra County (3B)
Arizona (5)
- Cochise County (3B)
- Graham County (3B)
- Greenlee County (3B)
- Mohave County (3B)
- Santa Cruz County (3B)
Missouri (2)
- Dunklin County (3A)
- Pemiscot County (3A)
Nevada (1)
- Clark County (3B)
Utah (1)
- Washington County (3B)
What changed in the 2021 map
98 of these counties moved here from zone 4 in the 2021 map. 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 3?
One of the eight US climate zones in the International Energy Conservation Code (IECC). Zone 3 has hot summers and mild winters. The code asks for an R-49 attic, R-20 walls (or R-13 plus R-5 foam) and R-10 foam along the slab edge, 2 ft deep. It covers 762 counties in 17 states.
How much attic insulation do I need in climate zone 3?
In zone 3, the 2021 IECC calls for R-49 in the attic of a new home. For an existing home, ENERGY STAR recommends R-49 in an uninsulated attic, or adding R-38 if you already have 3–4 inches.
Which states are in climate zone 3?
Texas, Georgia, North Carolina, Mississippi, Arkansas, Oklahoma, Alabama, South Carolina, California, Tennessee, Louisiana, Virginia, New Mexico, Arizona, Missouri, Nevada and Utah.
What do the letters A, B and C mean?
They describe moisture: 3A is humid, 3B is dry and 3C is marine (the mild, damp Pacific coast). In zone 3 the insulation minimums in the table above are the same for every letter.
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.