Title 24 Climate Zone 12: ADU Requirements
What the 2025 California Energy Code's prescriptive package requires for a new detached ADU in Climate Zone 12, and how those requirements change the MEP design.
Where Climate Zone 12 is
Of the California places we cover, 88 are mostly in Climate Zone 12, across 13 counties: Alameda County, Amador County, Calaveras County, Contra Costa County, El Dorado County, Mariposa County, Merced County, Sacramento County, San Joaquin County, Solano County, Stanislaus County, Tuolumne County, Yolo County. Together they issued 8,347 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 12, 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 0.613) / 1000 + 1.4; none required under 1.8 kWdc (about 653 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 12
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 89°F in Crockett to 100°F in Woodland, and the coldest winter design temperature is 18°F in Georgetown. 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 12
| Place | County | Electric utility | ADU permits 2021–25 |
|---|---|---|---|
| Sacramento | Sacramento | Sacramento Municipal Utility District (SMUD) | 1,720 |
| Modesto | Stanislaus | Modesto Irrigation District (MID) | 527 |
| Livermore | Alameda | Pacific Gas and Electric (PG&E) | 525 |
| Davis | Yolo | Pacific Gas and Electric (PG&E) | 384 |
| Tracy | San Joaquin | Pacific Gas and Electric (PG&E) | 330 |
| Concord | Contra Costa | Pacific Gas and Electric (PG&E) | 276 |
| Stockton | San Joaquin | Pacific Gas and Electric (PG&E) | 259 |
| Alamo (unincorp.) | Contra Costa | Pacific Gas and Electric (PG&E) | 219 |
| Vacaville | Solano | Pacific Gas and Electric (PG&E) | 206 |
| Pleasanton | Alameda | Pacific Gas and Electric (PG&E) | 199 |
| Folsom | Sacramento | Sacramento Municipal Utility District (SMUD) | 189 |
| Antioch | Contra Costa | Pacific Gas and Electric (PG&E) | 171 |
| Lafayette | Contra Costa | Pacific Gas and Electric (PG&E) | 171 |
| Woodland | Yolo | Pacific Gas and Electric (PG&E) | 164 |
| Citrus Heights | Sacramento | Sacramento Municipal Utility District (SMUD) | 152 |
| Pleasant Hill | Contra Costa | Pacific Gas and Electric (PG&E) | 152 |
| Walnut Creek | Contra Costa | Pacific Gas and Electric (PG&E) | 139 |
| Martinez | Contra Costa | Pacific Gas and Electric (PG&E) | 131 |
| Dublin | Alameda | Pacific Gas and Electric (PG&E) | 127 |
| Danville | Contra Costa | Pacific Gas and Electric (PG&E) | 126 |
| Pittsburg | Contra Costa | Pacific Gas and Electric (PG&E) | 113 |
| Manteca | San Joaquin | Pacific Gas and Electric (PG&E) | 103 |
| Brentwood | Contra Costa | Pacific Gas and Electric (PG&E) | 95 |
| Lodi | San Joaquin | Lodi Electric Utility | 94 |
| Los Banos | Merced | Pacific Gas and Electric (PG&E) | 84 |
| Orinda | Contra Costa | Pacific Gas and Electric (PG&E) | 81 |
| Fairfield | Solano | Pacific Gas and Electric (PG&E) | 79 |
| Placerville | El Dorado | Pacific Gas and Electric (PG&E) | 72 |
| West Sacramento | Yolo | Pacific Gas and Electric (PG&E) | 64 |
| Fair Oaks (unincorp.) | Sacramento | Sacramento Municipal Utility District (SMUD) | 64 |
| Shingle Springs (unincorp.) | El Dorado | Pacific Gas and Electric (PG&E) | 62 |
| Orangevale (unincorp.) | Sacramento | Sacramento Municipal Utility District (SMUD) | 60 |
| Carmichael (unincorp.) | Sacramento | Sacramento Municipal Utility District (SMUD) | 58 |
| Mariposa (unincorp.) | Mariposa | Pacific Gas and Electric (PG&E) | 57 |
| Elk Grove | Sacramento | Sacramento Municipal Utility District (SMUD) | 54 |
| San Ramon | Contra Costa | Pacific Gas and Electric (PG&E) | 51 |
| El Dorado Hills (unincorp.) | El Dorado | Pacific Gas and Electric (PG&E) | 51 |
| Ripon | San Joaquin | Pacific Gas and Electric (PG&E) | 45 |
| Ceres | Stanislaus | Turlock Irrigation District (TID) | 42 |
| Benicia | Solano | Pacific Gas and Electric (PG&E) | 42 |
| Bay Point (unincorp.) | Contra Costa | Pacific Gas and Electric (PG&E) | 39 |
| Oakley | Contra Costa | Pacific Gas and Electric (PG&E) | 37 |
| Copperopolis (unincorp.) | Calaveras | Pacific Gas and Electric (PG&E) | 36 |
| Lathrop | San Joaquin | Pacific Gas and Electric (PG&E) | 35 |
| Rancho Cordova | Sacramento | Sacramento Municipal Utility District (SMUD) | 31 |
| Diablo (unincorp.) | Contra Costa | Pacific Gas and Electric (PG&E) | 30 |
| Moraga | Contra Costa | Pacific Gas and Electric (PG&E) | 27 |
| Turlock | Stanislaus | Turlock Irrigation District (TID) | 26 |
| Merced | Merced | Pacific Gas and Electric (PG&E) | 25 |
| Keyes (unincorp.) | Stanislaus | Turlock Irrigation District (TID) | 25 |
| Rio Linda (unincorp.) | Sacramento | Sacramento Municipal Utility District (SMUD) | 24 |
| Wilton (unincorp.) | Sacramento | Sacramento Municipal Utility District (SMUD) | 24 |
| Waterford | Stanislaus | Modesto Irrigation District (MID) | 23 |
| Salida (unincorp.) | Stanislaus | Modesto Irrigation District (MID) | 23 |
| Suisun City | Solano | Pacific Gas and Electric (PG&E) | 22 |
| Dixon | Solano | Pacific Gas and Electric (PG&E) | 21 |
| Newman | Stanislaus | Pacific Gas and Electric (PG&E) | 21 |
| Valley Springs (unincorp.) | Calaveras | Pacific Gas and Electric (PG&E) | 21 |
| Murphys (unincorp.) | Calaveras | Pacific Gas and Electric (PG&E) | 20 |
| Antelope (unincorp.) | Sacramento | Sacramento Municipal Utility District (SMUD) | 18 |
| Cameron Park (unincorp.) | El Dorado | Pacific Gas and Electric (PG&E) | 17 |
| Camino (unincorp.) | El Dorado | Pacific Gas and Electric (PG&E) | 17 |
| Oakdale | Stanislaus | Pacific Gas and Electric (PG&E) | 16 |
| Riverbank | Stanislaus | Pacific Gas and Electric (PG&E) | 15 |
| Winters | Yolo | Pacific Gas and Electric (PG&E) | 15 |
| Clayton | Contra Costa | Pacific Gas and Electric (PG&E) | 15 |
| Denair (unincorp.) | Stanislaus | Turlock Irrigation District (TID) | 15 |
| Galt | Sacramento | Sacramento Municipal Utility District (SMUD) | 13 |
| Livingston | Merced | Pacific Gas and Electric (PG&E) | 13 |
| Elverta (unincorp.) | Sacramento | Sacramento Municipal Utility District (SMUD) | 13 |
| Gustine | Merced | Pacific Gas and Electric (PG&E) | 12 |
| San Andreas (unincorp.) | Calaveras | Pacific Gas and Electric (PG&E) | 11 |
| North Highlands (unincorp.) | Sacramento | Sacramento Municipal Utility District (SMUD) | 11 |
| Diamond Springs (unincorp.) | El Dorado | Pacific Gas and Electric (PG&E) | 9 |
| Wallace (unincorp.) | Calaveras | Pacific Gas and Electric (PG&E) | 8 |
| Sonora | Tuolumne | Pacific Gas and Electric (PG&E) | 7 |
| Escalon | San Joaquin | Pacific Gas and Electric (PG&E) | 7 |
| Herald (unincorp.) | Sacramento | Sacramento Municipal Utility District (SMUD) | 7 |
| Discovery Bay (unincorp.) | Contra Costa | Pacific Gas and Electric (PG&E) | 7 |
| Esparto (unincorp.) | Yolo | Pacific Gas and Electric (PG&E) | 7 |
| Byron (unincorp.) | Contra Costa | Pacific Gas and Electric (PG&E) | 7 |
| Acampo (unincorp.) | San Joaquin | Pacific Gas and Electric (PG&E) | 7 |
| Pine Grove (unincorp.) | Amador | Pacific Gas and Electric (PG&E) | 6 |
| Pacheco (unincorp.) | Contra Costa | Pacific Gas and Electric (PG&E) | 6 |
| Crockett (unincorp.) | Contra Costa | Pacific Gas and Electric (PG&E) | 5 |
| Georgetown (unincorp.) | El Dorado | Pacific Gas and Electric (PG&E) | 5 |
| Mokelumne Hill (unincorp.) | Calaveras | Pacific Gas and Electric (PG&E) | 5 |
| Catheys Valley (unincorp.) | Mariposa | Pacific Gas and Electric (PG&E) | 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.
Need MEP plans and a Title 24 report in Climate Zone 12?
We prepare both from the same design, so the energy model and the equipment on the plans agree.
Start My Order