Title 24 Climate Zone 16: ADU Requirements

Where Climate Zone 16 is

Of the California places we cover, 19 are mostly in Climate Zone 16, across 10 counties: Butte County, El Dorado County, Kern County, Lassen County, Los Angeles County, Mono County, Nevada County, Placer County, San Bernardino County, Trinity County. Together they issued 318 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 16, the 2025 prescriptive package sets these zone-specific targets.

Windows	U-factor 0.27 or lower; SHGC No limit; total area up to 20% of floor area
Attic, high-performance option	R-38 ceiling; below roof deck: R-19
Attic, ducts-inside option	R-38 ceiling; ducts and air handler in conditioned space
Framed walls	Assembly U-factor 0.048 or lower
Cool roof	Not required
Whole-house fan	Not required
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 0.59) / 1000 + 1.22; none required under 1.8 kWdc (about 983 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 16

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 79°F in South Lake Tahoe to 101°F in Mentone, and the coldest winter design temperature is -10°F in Truckee. 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 16

Place	County	Electric utility	ADU permits 2021–25
Sunland (Los Angeles)	Los Angeles	Los Angeles Department of Water and Power (LADWP)	584
Tujunga (Los Angeles)	Los Angeles	Los Angeles Department of Water and Power (LADWP)	562
Truckee	Nevada	Truckee Donner Public Utility District	117
South Lake Tahoe	El Dorado	Liberty Utilities	37
Big Bear Lake	San Bernardino	Bear Valley Electric Service	23
Mammoth Lakes	Mono	Southern California Edison (SCE)	22
Lake Arrowhead (unincorp.)	San Bernardino	Southern California Edison (SCE)	17
Big Bear City (unincorp.)	San Bernardino	Bear Valley Electric Service	17
Foresthill (unincorp.)	Placer	Pacific Gas and Electric (PG&E)	16
Mentone (unincorp.)	San Bernardino	Southern California Edison (SCE)	11
Tehachapi	Kern	Southern California Edison (SCE)	8
Susanville	Lassen	Lassen Municipal Utility District	8
Carnelian Bay (unincorp.)	Placer	Liberty Utilities	7
Weaverville (unincorp.)	Trinity	Trinity Public Utilities District	7
Forest Ranch (unincorp.)	Butte	Pacific Gas and Electric (PG&E)	6
Running Springs (unincorp.)	San Bernardino	Southern California Edison (SCE)	6
Crestline (unincorp.)	San Bernardino	Southern California Edison (SCE)	6
Magalia (unincorp.)	Butte	Pacific Gas and Electric (PG&E)	5
Janesville (unincorp.)	Lassen	Lassen Municipal Utility District	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.