Does a New ADU in Los Angeles Need Solar?

The California Energy Commission’s answer is short: “an ADU is considered a newly constructed building if it is a new, detached structure,” and a newly constructed detached ADU needs newly installed solar PV under Section 150.1(c)14 unless an exception applies. Attached ADUs, and conversions of unconditioned space such as a garage or storage room into living space, are additions under Section 150.2(a); solar PV is not required for them. Turning existing conditioned space — a basement or pool house — into an ADU or a junior ADU (up to 500 sq ft inside the house) is an alteration (CEC, 2025 Energy Code ADU FAQs).

The 2025 code applies to building permit applications filed from January 1, 2026 (California Building Standards Commission); an ADU that applied earlier stays under the 2022 code, whose PV formula and coefficients for the Los Angeles climate zones are the same.

The minimum comes from Equation 150.1-C: kW = (conditioned floor area × A) ÷ 1000 + (dwelling units × B), with A and B set by climate zone in Table 150.1-C. For a detached ADU there is one dwelling unit. Los Angeles spans several zones: in the Energy Commission’s ZIP-code list, San Fernando Valley and central ZIP codes such as 91324, 91406 and 90012 are zone 9; coastal ones such as 90049, 90291 and 90731 are zone 6; 90001 and 90044 are zone 8; and 91042 is zone 16 (CEC climate zones by ZIP).

A required 2 kW is about five 400-watt panels. Three more rules shape the number: the requirement cannot exceed what fits the solar access roof area — unshaded roof able to carry PV, measured on the ADU and any other new structures on the site — and no PV is required if that area is under 80 contiguous square feet; north-facing steep roof areas are left out; and pairing the PV with a battery that has at least 7.5 kWh of cycling capacity under Joint Appendix JA12 allows a 25% smaller array (Section 150.1(c)14, Exceptions 1, 2 and 5).

“The 2025 Energy Code does not specify where new solar PV modules must be installed,” the Energy Commission says: they must be on the same residential lot and meet the utility’s requirements. Two rules follow from its FAQ. An existing solar system on the main house cannot count toward a new detached ADU’s requirement — the PV must be newly installed. But new modules can be added to that existing system, and even an ADU on a separate meter can meet the requirement with modules added to the main house’s system that do not serve the ADU (CEC ADU FAQs). That lets the panels go on whichever roof on the lot has the best sun.

Two more Energy Code rules come with a new ADU. It must be battery-ready under Section 150.0(s) unless its electric service is 125 amps or less, and an installed battery system with all its wiring satisfies the rule. A new detached ADU that installs gas water heating, space heating, a gas cooktop or dryer must also meet the electric-ready requirements, so the wiring for a later switch is in place (CEC ADU FAQs).

LADWP. The utility handles meter-spot requests for single-family homes and ADUs with services up to 320 amps as a free service (LADWP). Its solar credits follow its own rules, not NEM 3.0: exported and imported kilowatt-hours net over each billing period, usually two months, and any excess becomes a credit that never expires but is never paid out (LADWP; see LADWP net metering). For interconnection, a system up to 30 kW without a service panel upgrade or multiple meters is Type 1; one with a service panel upgrade or a multi-meter interconnection goes through Type 2 (LADWP).

SCE. New systems are on the Net Billing Tariff, where exports earn hourly values — for customers who start in 2026 about 3¢ to 21¢ per kWh by season and hour (SCE) — well below what the account pays for imports. Size for use on the same meter and consider a battery; see NEM 3.0 explained.

In the City of Los Angeles every PV system needs an LADBS electrical permit (LADBS). For a new detached ADU the required PV is part of the unit’s Title 24 compliance documents submitted with the building permit; a subpanel, a service change or a separate meter adds electrical work of its own. Whether the property needs a panel or service upgrade is a load calculation — see do you need a main panel upgrade — and the local process is in solar permits in Los Angeles.

Bottom line: if you are building a new detached ADU, check its size against the table first — a small unit may need no solar at all, and a larger one about 2 kW, which can join the main house’s system. Decide the meter setup early, because it decides how the credits work. Attached units and conversions carry no solar requirement, though solar can still pay on its own. LADBS, your utility and a Title 24 analyst confirm the details for your address.

Figures on this page come from the primary sources below and, where noted, from Cali Energy calculations using the stated assumptions. Rates, incentives, and program terms change; each was verified September 30, 2026.

1. California Energy Commission — 2025 Building Energy Efficiency Standards (CEC-400-2025-010-F): Section 150.1(c)14, Equation 150.1-C, Table 150.1-C
2. California Energy Commission — 2025 Energy Code ADU FAQs (Energy Code Support Center)
3. California Energy Commission — Building climate zones by ZIP code
4. California Energy Commission — Climate zone tool and maps
5. California Building Standards Commission — 2025 Title 24 code changes (effective January 1, 2026)
6. LADWP — Type 1, 2 and 3 interconnection
7. LADWP — Request a meter spot for a single-family home or ADU up to 320 amps
8. LADWP — Service Rider NEM, Net Energy Metering
9. SCE — Solar Billing Plan (Energy Export Credit values)
10. LADBS — Information Bulletin P/GI 2023-027, Solar Energy Systems