Does a new ADU have to have solar panels? Sometimes yes. It depends mainly on whether the ADU is a new detached building, or whether it is built inside or onto an existing home. This guide explains the rule at a basic level and flags the details that we could not confirm.
LA ADU Guide is an information site. We are not an energy consultant, designer or solar installer, and we do not sell anything. The Energy Code is technical, so your designer and the building department decide how it applies to your project.
The basic rule
The California Energy Commission (CEC) writes the Building Energy Efficiency Standards, often called Title 24 Part 6 or the Energy Code. The 2022 code requires solar photovoltaic (PV) systems on newly constructed single-family buildings. The CEC's own answer for ADUs says: "The ADU must have a newly installed solar PV system to meet the requirements."
Three points from the CEC's page:
- An existing solar system on the main house cannot be counted for a new detached ADU.
- New modules can be added to an existing system. The CEC says "New solar PV modules may be added to an existing solar PV system to meet the 2022 Energy Code requirements," if they are "on the same residential lot as the ADU."
- The Energy Code does not regulate whether the added panels serve the ADU meter or the main house meter.
The requirement comes from section 150.1(c)14 of the Energy Code.
Which ADUs are covered
| ADU type | Solar PV requirement under the 2022 code |
|---|---|
| New detached ADU (new building) | Yes, per the CEC page, unless an exception applies |
| Attached ADU or addition | The CEC says the requirements "do not apply to additions or alterations to existing buildings" |
| Conversion of existing space (garage, spare room) | An alteration to an existing building; the CEC page does not address conversions directly, so confirm with your plan checker |
| JADU inside the home | An alteration inside an existing home |
A secondary source quoting HCD guidance says ADUs built within existing space or as an addition to an existing home, including detached additions where an existing non-residential building is converted, are not subject to the solar requirement. We could not find that text on the CEC page, so confirm it with the building department.
Exceptions
The CEC lists five general exceptions for single-family buildings, none specific to ADUs. They include a small amount of usable roof, described as under 80 contiguous square feet of solar access roof area (SARA), and a very small required system, under 1.8 kilowatts DC. Blogs describe other limits, with inconsistent numbers, so we do not repeat them. Ask your designer to run the calculation for your roof and orientation.
Also, the CEC says "solar ready is not applicable to a newly constructed ADU on an existing lot." So the separate "solar ready" rules for new homes do not apply to a new detached ADU.
How big must the system be
The Energy Code sizes the system using a formula (Equation 150.1-C) that depends on climate zone, the unit's conditioned floor area and the number of dwelling units. We cannot give a typical size. Your energy consultant or designer calculates it, and the CEC says added modules must be "sized per the Energy Code."
A new code cycle is coming and may have changed
The 2022 code was in force for permits for several years. California updates the code on a three-year cycle, and the 2025 code applies to permits from January 1, 2026, per the CEC's general program. We did not review the 2025 ADU solar language. Do not assume the 2022 answers above carry over. Ask your building department which edition applies to your application date.
Other energy paperwork for an ADU
Even if solar does not apply, the Energy Code still does. A new ADU, or a conversion, usually needs:
- insulation and window performance that meet the code, or a documented alternative
- efficient heating, cooling and water heating equipment, as chosen by the designer
- lighting and ventilation rules
- compliance forms prepared by a qualified preparer and included with the permit set (LADBS lists "Energy and green building documents" among typical application items)
Conversions, especially garages, often need new insulation, a new heating and cooling plan and new windows because the structure was never designed as a home. Ask for the energy review early, since it can change wall and roof thickness.
What it does to cost and timing
We do not have sourced numbers for the cost of solar on an ADU, so we do not give one. Cost depends on system size, roof, installer and any rebates, which change. Solar and its electrical work also add an inspection step. See ADU cost in Los Angeles for how to compare bids and ask that solar be listed as its own line.
Checklist
- [ ] Is the ADU a new detached building, an addition or a conversion?
- [ ] Which Energy Code edition applies on your application date?
- [ ] Does the plan checker agree a solar exception applies, if you claim one?
- [ ] Can you add modules to an existing array on the same lot?
- [ ] Who prepares the Energy Code compliance forms?
- [ ] Does the roof have enough clear space? Check shade, orientation and fire zone roof rules.
- [ ] Is solar a separate line in every bid?
- [ ] Which inspections cover the PV system?
Questions to ask the plan checker
- Does section 150.1(c)14 apply to my ADU?
- Will you accept panels added to the main house array?
- Is a documented exception (such as shade) acceptable, and what proof do you need?
- Which Energy Code edition governs my submittal?
See the permit process in Los Angeles and plan check and inspections for where energy review fits. For types of ADUs, see ADU vs. JADU vs. garage conversion. This page is general information, not legal advice.