Usually yes, if it is a new detached ADU. Under the 2025 California Energy Code, in effect since January 1, 2026, a newly built ADU that stands on its own is treated as a new building and needs a solar (PV) system. A new ADU that shares a wall with the house counts as an addition and does not. Garage conversions and conversions of existing living space do not need solar either.
The solar rule is not a Los Angeles rule. It comes from the California Energy Code (Title 24, Part 6), section 150.1(c)14, which applies the same way in every California city. The California Energy Commission's 2025 guide for ADUs spells out how it applies: the requirement covers newly constructed buildings, and it does not apply to additions or alterations. So the question that decides whether your ADU needs solar is simple to ask but easy to get wrong: is your ADU a new building, or an addition to one that already exists?
New building or addition?
The Energy Commission sorts ADUs by how they are built, not by what they are called. Here is how the common types land.
| Type of ADU | Solar required? | Code |
|---|---|---|
| New detached ADU | Yes (new construction), unless an exception applies | Energy Code 150.1(c)14 |
| New ADU joined to the house only by a breezeway or covered walkway | Yes (new construction) | Energy Code 150.1(c)14 |
| New ADU that shares a wall with the house | No (addition) | Energy Code 150.1(c)14 |
| New ADU built on top of an existing detached garage | No (addition; shares a floor and ceiling) | Energy Code 150.1(c)14 |
| Garage or other unconditioned structure converted to an ADU | No (addition) | Energy Code 150.1(c)14 |
| Existing conditioned space, such as a basement, converted to an ADU or JADU | No (alteration) | Energy Code 150.1(c)14 |
"Conditioned" means space that is heated or cooled, directly or indirectly. A typical garage is unconditioned, which is why converting one is treated as an addition of new living space rather than a remodel. Either way, it is not a new building, so solar is not required.
Why a breezeway does not count as attached
This is the case that catches people. A covered walkway between the house and a new backyard unit looks like it connects the two, but under the Energy Code the ADU is still a new building because it shares no wall, floor, or ceiling with the house. It needs solar just like a fully detached unit.
Attaching the ADU to the house for real changes more than the solar answer. Under state ADU law, an attached ADU can be as tall as 25 feet or the zone's height limit, whichever is lower, while a detached ADU is generally limited to 16 feet. Our guide to ADU rules in Los Angeles covers those limits. The layout should be chosen for how the unit lives, with the solar answer as one input, not the only one.
How big the system has to be
The minimum system size comes from a formula in the Energy Code (Equation 150.1-C) based on the ADU's conditioned floor area, using factors from a state table for your climate zone. A larger unit needs a larger system. The required size is also capped by the roof you actually have: the solar access roof area times 18 watts per square foot for steep roofs, or 14 watts per square foot for low-slope roofs.
Not every part of the roof counts as solar access roof area. Roof areas with less than 70 percent annual solar access are left out, as are steep roof faces pointing roughly north (between 300 and 90 degrees), and areas that other building code requirements keep clear, such as an occupied roof deck. On the other hand, the roofs of a new carport, covered parking, or other new structure on the site do count, so the panels do not always have to go on the ADU itself.
That formula is the standard (prescriptive) path. A design that uses the performance path still needs solar; the size is set from the unit's modeled electricity use, and solar cannot be traded away for other efficiency measures. Either way, the energy compliance report on your plans (the CF1R) documents the solar system for plan check.
When a new ADU can skip solar
Two exceptions in section 150.1(c)14 remove the requirement for some new ADUs:
- Not enough usable roof: no solar is required when the solar access roof area is less than 80 contiguous square feet.
- Too small a system: no solar is required when the minimum system the formula calls for is less than 1.8 kWdc.
A third option, on the prescriptive path, reduces the system rather than removing it. When a battery storage system that meets the Energy Code's battery requirements (Joint Appendix JA12, with at least 7.5 kWh of capacity) is installed, the required solar size may be reduced by 25 percent.
Whether a particular ADU falls under one of these exceptions depends on its size, roof, shade, and climate zone, so it is worked out in the energy calculations for that design, not assumed.
What this means for your plans
If you are building a new detached ADU, plan for solar from the start and budget for it as part of the project. If you are converting a garage or adding an attached unit, solar is optional. Either way, the classification of your ADU drives more than solar under the Energy Code, so it is worth settling before design gets far. We design, permit, and build ADUs as one team; see our ADU builder in Los Angeles page for how we work, and how long LA ADU permits take for the approval timeline.
Look up your address on ZIMAS, the City of Los Angeles's online zoning map. It shows your lot's zone and any specific plan or overlay district, such as a historic district (HPOZ), where exterior work, even paint and landscaping, needs review before it starts. Then look at your backyard from above: shade from trees and neighboring buildings, and which way a new roof could face, both affect the solar answer.
Common questions
Does a garage conversion ADU need solar?
No. Converting an existing unconditioned garage, attached or detached, into an ADU is treated as an addition under the California Energy Code, and the solar requirement in section 150.1(c)14 does not apply to additions.
Does an attached ADU need solar?
Not if it shares a wall with the existing house; that makes it an addition. An ADU connected to the house only by a breezeway or covered walkway is treated as new construction and does need solar.
Can a new detached ADU skip solar?
Sometimes. No solar is required when the solar access roof area is less than 80 contiguous square feet, or when the minimum system the formula calls for is less than 1.8 kWdc. Installing a qualifying battery can reduce the required solar size by 25 percent.
CEC 2025 Energy Code ADU guide | CEC 2025 single-family solar PV requirements | CEC 2025 Residential Compliance Manual, Chapter 7 | HCD ADU Handbook (March 2026) | LA City Planning HPOZ review
Rules change and every lot is different. This guide is general information, not advice for your property; confirm the rules for your lot before you design or build.