Title 24 Climate Zone 11: ADU Requirements
What the 2025 California Energy Code's prescriptive package requires for a new detached ADU in Climate Zone 11, and how those requirements change the MEP design.
Where Climate Zone 11 is
Of the California places we cover, 26 are mostly in Climate Zone 11, across 7 counties: Butte County, Nevada County, Placer County, Shasta County, Sutter County, Tehama County, Yuba County. Together they issued 1,125 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 11, 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 0.836) / 1000 + 1.44; none required under 1.8 kWdc (about 431 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 11
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 92°F in Nevada City to 103°F in Rocklin, and the coldest winter design temperature is 14°F in Nevada City. 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 11
| Place | County | Electric utility | ADU permits 2021–25 |
|---|---|---|---|
| Chico | Butte | Pacific Gas and Electric (PG&E) | 218 |
| Granite Bay (unincorp.) | Placer | Pacific Gas and Electric (PG&E) | 131 |
| Roseville | Placer | Roseville Electric Utility | 128 |
| Auburn | Placer | Pacific Gas and Electric (PG&E) | 105 |
| Redding | Shasta | Redding Electric Utility | 77 |
| Rocklin | Placer | Pacific Gas and Electric (PG&E) | 76 |
| Lincoln | Placer | Pacific Gas and Electric (PG&E) | 46 |
| Loomis | Placer | Pacific Gas and Electric (PG&E) | 46 |
| Newcastle (unincorp.) | Placer | Pacific Gas and Electric (PG&E) | 33 |
| Nevada City | Nevada | Pacific Gas and Electric (PG&E) | 32 |
| Grass Valley | Nevada | Pacific Gas and Electric (PG&E) | 29 |
| Penryn (unincorp.) | Placer | Pacific Gas and Electric (PG&E) | 29 |
| Palo Cedro (unincorp.) | Shasta | Pacific Gas and Electric (PG&E) | 25 |
| Meadow Vista (unincorp.) | Placer | Pacific Gas and Electric (PG&E) | 22 |
| Yuba City | Sutter | Pacific Gas and Electric (PG&E) | 21 |
| Olivehurst (unincorp.) | Yuba | Pacific Gas and Electric (PG&E) | 15 |
| Durham (unincorp.) | Butte | Pacific Gas and Electric (PG&E) | 14 |
| Oroville | Butte | Pacific Gas and Electric (PG&E) | 11 |
| Shasta Lake | Shasta | City of Shasta Lake Electric Utility | 11 |
| Red Bluff | Tehama | Pacific Gas and Electric (PG&E) | 11 |
| Cottonwood (unincorp.) | Shasta | Pacific Gas and Electric (PG&E) | 10 |
| Anderson | Shasta | Pacific Gas and Electric (PG&E) | 9 |
| Penn Valley (unincorp.) | Nevada | Pacific Gas and Electric (PG&E) | 9 |
| Shingletown (unincorp.) | Shasta | Pacific Gas and Electric (PG&E) | 7 |
| Sheridan (unincorp.) | Placer | Pacific Gas and Electric (PG&E) | 5 |
| Plumas Lake (unincorp.) | Yuba | 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 11?
We prepare both from the same design, so the energy model and the equipment on the plans agree.
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