ADU Solar Requirements in California: What Detached Units Need in 2026

Under the 2025 California Energy Code, in force since January 1, 2026, a newly built detached ADU is treated as a new single family home and must include its own solar photovoltaic system unless one of five code exceptions applies. Attached ADUs, garage conversions, and junior ADUs carved out of existing space are classified as additions or alterations, and the new construction solar mandate does not reach them. The rule turns on how your permit classifies the project, not on whether the unit has its own front door, which is why an experienced ADU construction team settles that classification before the first drawing.

The required system for a typical Los Angeles backyard unit is small, usually under 2.5 kilowatts, and the panels do not even have to sit on the ADU roof. What follows covers exactly who the rule applies to, how the size is calculated for each Los Angeles climate zone, the exceptions that remove it, and what a compliant system costs in 2026 now that the federal residential credit is gone.

Key Takeaways

Solar is mandatory only for newly constructed detached ADUs. Attached units, garage conversions, and JADUs inside existing space are outside the new construction PV requirement.

The minimum size comes from Equation 150.1-C. In Climate Zone 9, an 800 square foot detached ADU needs about 1.85 kWdc, and units under roughly 718 square feet fall below the 1.8 kW threshold and need no system at all.

The new modules can go on the main house roof, a carport, or the ground, as long as they are new panels on the same lot permitted with the ADU. An existing array does not count.

Homes destroyed in the January 2025 fires can rebuild without the solar mandate under Executive Order N-29-25, and LADBS has confirmed it is not enforcing PV on those rebuilds.

The federal residential solar credit ended for systems placed in service after December 31, 2025, so a 2026 ADU budget should carry the full installed cost.

Why the solar mandate reaches some ADUs and skips others

Section 150.1(c)14 of Title 24, Part 6 requires a solar PV system on every newly constructed single family residential building. The California Energy Commission defines a newly constructed building as one that has never been used or occupied for any purpose, and its 2025 ADU guidance says plainly that a new detached ADU is exactly that. A detached unit therefore has to satisfy the same prescriptive solar requirement as a new house, sized to the unit rather than to the main residence.

The same guidance treats an attached ADU as an addition, because an addition is any change that increases conditioned floor area and conditioned volume. Converting an unconditioned garage or storage building into living space is also an addition, whether that structure is attached to the house or standing on its own in the yard. Additions follow Section 150.2(a), which carries insulation, glazing, water heating and ventilation rules but not the solar mandate. Converting space that was already conditioned, such as a finished pool house or a heated basement, is an alteration under Section 150.2(b), and only the components you touch have to comply.

Two edge cases trip people up. A manufactured home with a HUD label is regulated under Title 25 and sits outside the Energy Code entirely, while a factory built modular ADU set on a permanent foundation must comply with Title 24 exactly like site built construction. And if you demolish an old detached garage and build a fresh structure in its place, LADBS can reasonably classify the result as new construction rather than an addition, so confirm the classification before you assume the conversion exemption applies. The detached versus attached ADU decision carries more weight in 2026 than most owners expect for this reason alone.

Project type	Energy Code classification	Solar PV required?	Notes
Detached ADU built from the ground up	Newly constructed building	Yes, unless an exception applies	Sized by Equation 150.1-C or solar access roof area
Attached ADU sharing a wall, floor or ceiling	Addition	No	Section 150.2(a) addition rules still apply
Detached garage converted to an ADU	Addition	No	Insulation, cool roof and lighting rules apply to the converted envelope
Old garage demolished, new detached ADU built	Usually newly constructed	Usually yes	Confirm classification with LADBS before relying on the conversion exemption
Conversion of a conditioned pool house or basement	Alteration	No	Only altered components must comply
JADU inside a newly built house	Part of the new house	Covered by the house’s own PV	No separate ADU system
HUD labeled manufactured home used as an ADU	Outside Title 24, Part 6	No	Title 25 governs the unit; local placement rules still apply
Factory built modular ADU on a foundation	Newly constructed building	Yes	Complies with Title 24 like site built work

How the required system size is calculated for a Los Angeles ADU

The prescriptive path gives you two numbers and lets you install the smaller one. The first is capacity based on solar access roof area, or SARA, at 18 watts per square foot for steep sloped roofs and 14 watts per square foot for low sloped roofs. The second comes from Equation 150.1-C: kWPV = (CFA × A) / 1000 + (NDU × B), where CFA is conditioned floor area, NDU is the number of dwelling units, and A and B are climate zone factors from Table 150.1-C. The equation approximates the electricity a mixed fuel home would use, so choosing heat pumps or an induction range does not increase the size you are required to install.

Climate zone is the variable that changes the answer across Los Angeles. The coastal strip around Santa Monica, Venice, Pacific Palisades and Torrance sits in Climate Zone 6. Downey, Norwalk and the southeast county toward Fullerton are Climate Zone 8. Central Los Angeles, Hollywood, and the San Fernando Valley, including Valley Village and Sherman Oaks, are Climate Zone 9, and the mountain communities fall into Climate Zone 16. Confirm your own parcel with the CEC’s climate zone lookup tool, because zone lines do not follow city boundaries. The table below applies the Table 150.1-C factors published in the CEC’s 2025 Single-Family Residential Compliance Manual to common ADU sizes. Treat these as planning estimates, because your Title 24 consultant will run the binding number in CBECC-Res, and the performance path can move it slightly.

Climate zone	Typical LA areas	A factor	B factor	Exempt below (approx.)	800 sq ft	1,000 sq ft	1,200 sq ft
CZ 6	Santa Monica, Pacific Palisades, Venice, Torrance	0.594	1.23	960 sq ft	1.71 kW (exempt)	1.82 kW	1.94 kW
CZ 8	Downey, Norwalk, southeast county toward Fullerton	0.586	1.37	734 sq ft	1.84 kW	1.96 kW	2.07 kW
CZ 9	Central LA, Hollywood, San Fernando Valley, Valley Village	0.613	1.36	718 sq ft	1.85 kW	1.97 kW	2.10 kW
CZ 16	Mountain communities	0.59	1.22	983 sq ft	1.69 kW (exempt)	1.81 kW	1.93 kW

A worked example makes the math concrete. A 900 square foot detached ADU in Valley Village, Climate Zone 9, needs (900 × 0.613) / 1000 + (1 × 1.36), which is 0.55 + 1.36, or 1.91 kWdc. With today’s 400 to 440 watt residential modules that is five panels, delivering about 2.0 to 2.2 kW installed, which fits comfortably on one side of a small gable. The same unit in Pacific Palisades would need 1.76 kWdc, which lands under the 1.8 kW line and is exempt. Two identical drawings, two different answers, purely because of the climate zone.

The five exceptions and which ones ADU owners actually use

Exception 1 removes the requirement when the solar access roof area is less than 80 contiguous square feet. On steep sloped roofs, SARA excludes any roof plane facing between 300 and 90 degrees from true north, so a north facing shed roof contributes nothing, and it also excludes areas with less than 70 percent annual solar access because of existing trees, hills or neighboring buildings. Exception 2 is the one most small ADUs lean on: if the minimum size from Section 150.1(c)14 works out below 1.8 kWdc, no system is required at all. Exception 3 covers snow loads and is irrelevant in Los Angeles, and Exception 4 applies only to plans approved by a planning department before January 1, 2020.

Exception 5 is different in kind. If you install a battery energy storage system that meets Reference Joint Appendix JA12 with at least 7.5 kWh of cycling capacity, the Equation 150.1-C size can be reduced by 25 percent. The Energy Commission is explicit that you cannot stack Exception 2 and Exception 5, and choosing Exception 5 means you commit to installing both the panels and the battery. For an ADU that already lands near 2 kW, cutting the array to 1.5 kW while adding a battery rarely saves money, so the battery path only makes sense when you want backup power anyway.

One detail catches owners who count on shading. For steep roofs, only permanent obstructions external to the building reduce SARA, so a large jacaranda on the neighbor’s side of the fence counts, while your own chimney or a parapet you designed does not. On low sloped roofs every obstruction counts, including features of your own building. If you are hoping to qualify under Exception 1, have the solar access documented with a shade study before plan check rather than arguing the point with a plan checker afterward.

The panels do not have to sit on the ADU roof

The 2025 code does not dictate where the new modules go. According to the Energy Commission’s own FAQ, new PV modules can be added to an existing array on the main house, mounted on a carport, or ground mounted, and the requirement is satisfied as long as the modules are new, sit on the same residential lot as the ADU, are included in the ADU’s permit application, are sized to the code, and the utility allows the system expansion. It does not matter whether those modules feed the ADU meter or the main house meter.

The limit is just as clear. An existing solar system, however large, cannot be counted toward the ADU requirement. Newly constructed detached ADUs must have newly installed PV unless an exception applies, so an owner with an oversized 10 kW array on the house still has to add roughly 2 kW of new modules for the backyard unit. In practice that often means checking whether the existing inverter has headroom, and if it does not, budgeting for microinverters or a second string inverter. The performance path also allows a CEC approved community shared solar program to stand in for on-site panels where one exists for your utility, which is worth asking your Title 24 consultant about.

Solar ready provisions under Section 110.10 are a separate concept that confuses ADU owners. Those rules apply to new single family homes in subdivisions of ten or more lots, so a detached ADU on an existing lot has no solar ready obligation, and a unit that qualifies for an exception has neither a PV requirement nor a solar ready requirement. If you are working through a garage conversion ADU, none of this section applies to you at all because the project is an addition, not new construction.

What else the 2025 Energy Code asks of a new detached ADU

Solar is the headline, but the 2025 code layers several electrical readiness rules onto a detached unit. A newly constructed ADU must meet the battery energy storage system ready requirements of Section 150.0(s) unless its electrical service is 125 amps or less. Where it applies, the panel needs a 225 amp busbar rating, which a clearly labeled 200 amp panel can satisfy, and a subpanel fed from a main house panel with that busbar rating is acceptable. The interconnection equipment must provide 60 amps of backup capacity and four battery supplied branch circuits, or you can simply install a working battery and satisfy the section outright.

Gas appliances trigger electric ready wiring under Sections 150.0(n) and 150.0(t) through (v), so a gas range still needs a 240 volt circuit stubbed nearby. Water heating is prescriptively a heat pump, though a unit of 500 square feet or less can use an electric point of use heater with short pipe runs under Exception 1 to Section 150.1(c)8. Mandatory ventilation for indoor air quality applies at every size, and ADU additions of 700 square feet or less are excused from quality insulation installation verification. The step-by-step sequence in our guide on how to build an ADU in Los Angeles shows where the Title 24 report lands in the LADBS submittal.

These rules will stay put for a while. Through AB 130, signed with the 2025 state budget, California froze changes to residential building standards from October 1, 2025 until June 1, 2031, with exceptions for emergency health and safety measures and home hardening. The 2025 code cycle that took effect in January 2026 was carried through, so the solar and readiness requirements described here are the rules you will design to for the rest of the decade, even as the zoning side keeps moving under the California ADU laws 2026 changes.

Los Angeles specifics: LADBS, LADWP, and the fire rebuild exemption

In the City of Los Angeles, LADBS reviews the CF1R energy forms with the building plans, and the PV array appears on the plan set at plan check rather than as an afterthought.

The utility matters more than most owners realize. LADWP is a municipal utility outside the CPUC’s authority, so it still runs its own net energy metering with export credits near retail value, which means a solar only system on a city lot generally pencils without a battery. Homeowners in Southern California Edison territory, which covers parts of Los Angeles County, fall under the Net Billing Tariff for interconnections filed since April 15, 2023, where exported power is credited at a far lower avoided cost value and storage becomes the standard design.

Fire rebuilds are the major carve out. Governor Newsom’s Executive Order N-29-25, issued July 7, 2025, allows homes destroyed in the January 2025 fires to rebuild under the 2022 building code instead of the 2025 standards and suspends the rooftop solar requirement for those reconstructions, and the LADBS wildfire FAQ confirms that PV systems are not required on those projects. New detached ADUs are allowed on Palisades rebuild lots and are not bound by the 110 percent footprint rule, but ask LADBS in writing whether the solar relief extends to the ADU before you design without panels. Owners in the Valley who are adding a unit to an undamaged home get no such relief, which is why Valley Village general contractors should be pricing the array into every detached ADU bid in 2026.

The incentive picture changed at the end of 2025. The federal Residential Clean Energy Credit under Section 25D is no longer available for expenditures made after December 31, 2025, so a homeowner who buys the system outright in 2026 should not subtract 30 percent from the quote. Third party owned systems under leases or power purchase agreements may still carry commercial credits for a period, and that structure can make sense for an ADU that will be rented, but it deserves a conversation with a tax professional rather than an assumption.

What a compliant ADU solar system costs in 2026

Small systems cost more per watt than full size arrays because permits, interconnection, the inverter, monitoring and the crew’s day on site are fixed costs spread across fewer panels. EnergySage marketplace data in early 2026 averaged about $2.58 per watt for typical residential systems, while Lawrence Berkeley National Laboratory’s report on 2024 cash purchases put the median installed price near $3.50 per watt, and 2 to 3 kW systems sit at the top of that spread. The figures below are a planning range drawn from those published national sources, not a quote, and Los Angeles labor pushes toward the top of each band.

Item	Planning range	What drives it
2 to 2.5 kW rooftop system on the ADU (5 to 7 panels)	$6,000 to $10,000	Fixed permit, interconnection and inverter costs; roof type and access
Adding 2 kW of modules to an existing main house array	$4,000 to $8,000	Inverter headroom; microinverters or a second inverter if none
Ground mount or carport mount instead of the ADU roof	Add $2,000 to $6,000	Racking, trenching, conduit runs to the panel
JA12 battery (10 to 13.5 kWh) for Exception 5 or backup	$12,000 to $18,000	Capacity, backup gateway, panel work
Title 24 energy compliance report (CF1R)	$400 to $1,000	Prescriptive versus performance modeling

Set against a full build, the array is a small line. Our breakdown of ADU cost in Los Angeles puts a detached unit well into six figures, so a $7,000 solar system is usually a low single digit percentage of the project and, under LADWP net metering, one of the few line items that pays the owner back. Where it does bite is on tight lots where roof orientation forces a ground mount or where an aging main panel needs replacement to accept the interconnection.

Design moves that keep the requirement from becoming a problem

Roof geometry decides most of it. A simple gable or shed roof with one plane facing south, east or west gives you SARA to spare, while a hipped roof chopped into small planes can leave you short of contiguous area and force panels onto the main house. Keep the array plane clear of the plumbing vents, the range hood duct and the mini split line set, because moving those later costs more than moving them on paper. The California Fire Code’s rooftop access pathway rules apply to residential PV, so the array location has to be coordinated with the fire access layout, and on a small ADU roof that coordination is far easier in the design phase than in the field.

Electrical planning follows the same logic. Run the PV conduit and the battery ready conduit during framing, land the ADU subpanel where the inverter can sit in shade, and confirm the main house service can carry the added load before LADWP interconnection. If the existing home already has solar, get the inverter model and its remaining capacity from the original installer early, because that single fact decides whether the ADU’s modules cost $4,000 or $8,000. Our complete ADU guide covers the rest of the site planning that has to line up with these decisions.

Conclusion

The California ADU solar rule is narrower than the headlines suggest and more predictable than most owners fear. Only newly constructed detached units have to include PV, the required size for a Los Angeles backyard home is usually two kilowatts or less, and units under roughly 720 square feet in the Valley or 960 square feet on the coast are exempt outright.

What changed for 2026 is the context around the rule. The 2025 code is in force and frozen through 2031, the federal residential credit is gone, LADWP net metering still makes a solar only system worthwhile, and fire rebuild lots have their own exemption. Settle the classification, run the equation for your climate zone, and design the roof to carry the answer before the plans go to LADBS.