Title 24 Climate Zone 14: ADU Requirements

Where Climate Zone 14 is

Of the California places we cover, 18 are mostly in Climate Zone 14, across 3 counties: Kern County, Los Angeles County, San Bernardino County. Together they issued 1,761 ADU building permits from 2021 through 2025. Zones follow ZIP-code boundaries, so we confirm the zone from the project address before running the Title 24 report.

2025 prescriptive requirements for a new detached ADU

For a new detached ADU in Climate Zone 14, the 2025 prescriptive package sets these zone-specific targets.

Windows	U-factor 0.27 or lower; SHGC 0.23 or lower; total area up to 20% of floor area (west-facing up to 5%)
Attic, high-performance option	R-38 ceiling; below roof deck: R-19
Attic, ducts-inside option	R-38 ceiling plus radiant barrier; ducts and air handler in conditioned space
Framed walls	Assembly U-factor 0.048 or lower
Cool roof	Required: steep-sloped roofs need aged solar reflectance 0.2 or higher and thermal emittance 0.75 or higher.
Whole-house fan	Required, 1.5 cfm per sq ft of floor area (units of 500 sq ft or less exempt)
Space heating and cooling	Heat pump (other systems through the performance approach)
Water heating	Heat pump water heater; units of 500 sq ft or less, or one bedroom or fewer, have simpler options
Solar PV	kW = (floor area x 0.741) / 1000 + 1.26; none required under 1.8 kWdc (about 729 sq ft or smaller for a single ADU)

An attached ADU or a garage conversion is an addition under the Energy Code, not new construction, so it follows the addition requirements instead. Solar PV is not required for additions.

Design temperatures across Climate Zone 14

The zone sets the energy targets, but the HVAC is sized from the local design temperature, and that varies inside a zone. Among the places we cover here, the 1% summer design temperature ranges from 100°F in Hesperia to 106°F in Twentynine Palms, and the coldest winter design temperature is 12°F in Lancaster. That spread is why we run a Manual J for each address instead of using a zone-wide rule of thumb.

Places in Climate Zone 14

Place	County	Electric utility	ADU permits 2021–25
Lancaster	Los Angeles	Southern California Edison (SCE)	1,013
Palmdale	Los Angeles	Southern California Edison (SCE)	292
Hesperia	San Bernardino	Southern California Edison (SCE)	105
Victorville	San Bernardino	Southern California Edison (SCE)	76
Apple Valley	San Bernardino	Southern California Edison (SCE)	76
Joshua Tree (unincorp.)	San Bernardino	Southern California Edison (SCE)	50
Ridgecrest	Kern	Southern California Edison (SCE)	27
Littlerock (unincorp.)	Los Angeles	Southern California Edison (SCE)	27
Yucca Valley	San Bernardino	Southern California Edison (SCE)	21
Phelan (unincorp.)	San Bernardino	Southern California Edison (SCE)	16
Adelanto	San Bernardino	Southern California Edison (SCE)	9
Rosamond (unincorp.)	Kern	Southern California Edison (SCE)	9
Oak Hills (unincorp.)	San Bernardino	Southern California Edison (SCE)	9
Piñon Hills (unincorp.)	San Bernardino	Southern California Edison (SCE)	8
Twentynine Palms	San Bernardino	Southern California Edison (SCE)	7
Acton (unincorp.)	Los Angeles	Southern California Edison (SCE)	6
Barstow	San Bernardino	Southern California Edison (SCE)	5
Morongo Valley (unincorp.)	San Bernardino	Southern California Edison (SCE)	5

Sources

• 2025 Building Energy Efficiency Standards (Title 24, Part 6), Section 150.1(c) and Table 150.1-A
• 2025 Single-Family Residential Compliance Manual (CEC-400-2025-005)

Requirements shown are the 2025 prescriptive package (effective January 1, 2026) for newly constructed single-family buildings, which includes new detached ADUs. A performance (computer-modeled) approach can trade some items against others. Your Title 24 report confirms what applies to your project.