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IECC Climate Zone 3B — Warm-Dry (Los Angeles, Las Vegas, Phoenix)

Updated Mar 25, 2026
Warm-dry climate with mild winters and hot dry summers. Minimal heating needs. Primary concern is cooling load and solar heat gain. Seismic Design Category D-E in California. Wildfire risk zones.

Climate Zone 3B covers Southern California, Southern Nevada, and Arizona. Climate characteristics: hot dry summers (design cooling 100-115F in desert areas, 85-95F coastal), mild winters (design heating 35-45F coastal, 25-35F inland). 1500-3000 HDD65, 1500-3500 CDD65. Insulation requirements (IECC 2024 residential): wall R-20 or 13+5ci, ceiling R-49, floor R-19. Window: U-0.30, SHGC 0.25 (critical — solar heat gain is the dominant load). Air barrier: max 3 ACH50. LA-specific: Title 24 energy code is MORE stringent than IECC. Seismic: Design Category D-E (very high seismic). Wind: 85-110 mph. Wildfire: extensive WUI (Wildland-Urban Interface) zones require Chapter 7A fire-resistant construction. Concrete: hot weather protection required (ACI 305) Apr-Oct. Radon: generally low risk. Scheduling: year-round construction possible, extreme heat limits outdoor work Jun-Sep in desert.

TAGS
climatezone-3blos-angeleswarm-dryseismicwildfiretitle-24
DETAILS
wind
{"basic_speed_mph":95,"exposure_category":"C"}
seismic
{"sd1":0.6,"sds":1.5,"design_category":"D"}
iecc zone
3
ashrae zone
3B
degree days
{"cdd_65":1800,"hdd_65":1500}
design temps
{"cooling_1pct_f":89,"heating_99pct_f":43}
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