Zone 4B covers 66 counties in 7 states, home to about 2,488,565 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 4B
| 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 4B counties fall in the mixed-dry Building America region. Dry air, cold nights and hot days: wide temperature swings, wildfire smoke and freezes.
The “B” (dry) regime means low humidity, high sun and often hard water: sealants, roof coverings and water-using appliances wear faster.
See this month’s tasks for the mixed-dry region.
Largest counties in zone 4B
Bernalillo County, NM675,855Yavapai County, AZ235,830El Dorado County, CA190,978Randall County, TX140,728Potter County, TX118,502Valencia County, NM75,987Lake County, CA68,074Lyon County, NV59,117Carson City, NV58,597Tuolumne County, CA55,536Gila County, AZ53,118Nye County, NV51,166Douglas County, NV49,429Curry County, NM48,395Calaveras County, CA45,237Amador County, CA40,427Hale County, TX32,413Grant County, NM28,092Texas County, OK21,380Hockley County, TX21,365Moore County, TX21,335Gray County, TX21,215Hutchinson County, TX20,595Lincoln County, NM20,041Roosevelt County, NM19,167Inyo County, CA18,979Otero County, CO18,678Deaf Smith County, TX18,563Mariposa County, CA17,060Socorro County, NM16,505Trinity County, CA15,882Las Animas County, CO14,491Lamb County, TX13,016Prowers County, CO11,979Ochiltree County, TX10,012Parmer County, TX9,859Quay County, NM8,718Yoakum County, TX7,671Castro County, TX7,365Dallam County, TX7,070Swisher County, TX6,962Bailey County, TX6,899Carson County, TX5,799Bent County, CO5,639Hartley County, TX5,380Floyd County, TX5,371Hansford County, TX5,283Beaver County, OK5,045Mineral County, NV4,516Lincoln County, NV4,449Guadalupe County, NM4,420Union County, NM4,072Catron County, NM3,556Baca County, CO3,490Donley County, TX3,257Lipscomb County, TX3,059Sherman County, TX2,781Cochran County, TX2,539Cimarron County, OK2,285 States in this zone: Texas (28), New Mexico (13), California (8), Nevada (7), Colorado (5), Oklahoma (3), Arizona (2).