Does a New ADU Need Solar Panels Under Title 24 in California?

Does a new ADU actually need solar under Title 24?

Title 24 is California's building code, and Part 6 is the energy code — the Building Energy Efficiency Standards written by the California Energy Commission and adopted by the Building Standards Commission. Since the 2019 code took effect on January 1, 2020, every newly constructed low-rise residential dwelling in California has had to include a solar photovoltaic (PV) system. That mandate did not carve out accessory dwelling units. A detached ADU is a brand-new dwelling with its own conditioned floor area, so the plan checker treats it the way they'd treat a new single-family home: it needs PV sized to the unit.

The size is not a round number a contractor picks. The energy code sets the required system in kilowatts using an equation driven by the ADU's conditioned floor area and its climate zone, then your Title 24 energy consultant runs it through Energy Commission-approved compliance software and hands the building department a signed compliance document. For a typical 400–1,200 sq ft ADU that lands in the low single-digit kilowatts — a small array, not a full rooftop.

Two things trip homeowners up here. First, the requirement is enforced by the local building department at plan check — the City of Sacramento's Community Development Department, Sacramento County's Building Permits & Inspection Division, or a foothill county's building division — not by SMUD or PG&E. Second, whether it applies at all depends entirely on how your ADU is built. New detached construction is the case that triggers it. Conversions and additions usually don't, and that distinction is where most of the money is.

Which ADUs trigger the solar mandate — and which are exempt

The energy code splits work into three buckets: newly constructed buildings, additions, and alterations. Only the first bucket carries the full new-construction PV requirement. A detached ADU is a new building. An attached ADU welded onto an existing house is generally treated as an addition, and converting a garage or carving a Junior ADU out of existing interior space is an alteration. Additions and alterations follow their own, lighter energy provisions that typically do not require you to install a new PV system.

That is the single most valuable thing to understand before you design. The same 700 sq ft of living space can carry a solar requirement as a detached unit and carry none as a garage conversion. It's also why the answer to "does my ADU need solar" is genuinely "it depends on the type" — not a dodge, but the actual structure of the code.

See also:Detached ADU builds — the type that carries the solar requirement · Garage conversion ADUs — typically exempt as an alteration

How big a solar system does a Sacramento ADU actually need?

The required PV size scales with two inputs: the ADU's conditioned floor area and the California Energy Commission climate zone the parcel sits in. The valley floor across most of Sacramento County and the City of Sacramento is CEC Climate Zone 12; foothill parcels in Placer and El Dorado counties can fall into Zone 11 or the higher mountain zones, which changes the sizing factor. Your Title 24 consultant plugs the exact numbers into the compliance software — the ranges below are what those systems typically produce for ADU-scale units, not code values you can quote to a plan checker.

Because a kitchen, a meter, a small inverter, and the labor to get a crew on the roof are largely fixed costs, small arrays cost more per watt than big ones. That's why a 1.5 kW system on a studio doesn't cost a third of a 4.5 kW system on a house. Treat every dollar figure here as a 2026 Sacramento-region market estimate — confirm your actual number with your installer and your Title 24 report.

The exceptions and alternatives to panels on the ADU roof

"Detached ADU needs PV" is the default, not an absolute. The energy code builds in several exceptions and compliance paths, and a good Title 24 consultant checks all of them before assuming your budget takes the hit:

None of these are loopholes — they're written into the standard. But each has to be documented in the compliance software and accepted at plan check, so it's a design-phase conversation, not something you bolt on later.

• Limited solar access / small roof: if shading or available roof area won't support the calculated system, the code allows a reduced system or an exemption — common on tree-canopied central-city lots.
• Battery storage credit: pairing a battery with the array can earn a compliance credit that lets you install a smaller PV system while still passing.
• Community / shared solar: where a qualifying community-solar program is available, the code may permit it as an alternative to rooftop panels — SMUD's SolarShares is the local example in its territory, though you'll need to confirm the program qualifies for Title 24 compliance.
• Ground-mount or garage/carport array: on sloped foothill lots or where the ADU roof faces the wrong way, the required PV can sometimes sit on a better-oriented surface on the same property.
• Insufficient roof after other loads: solar water heating or roof equipment can reduce the usable area the calculation assumes.

SMUD vs PG&E: why your utility changes the solar math

Two different utilities serve the four-county region, and they play by different rules for solar. Most of Sacramento County and the City of Sacramento are in SMUD territory. El Dorado County, most of Placer County (Auburn, Loomis, Granite Bay, El Dorado Hills, Cameron Park), and Yolo / West Sacramento are PG&E. That line matters because it decides how your ADU's panels get interconnected and how the power they produce is credited.

SMUD is a publicly owned utility, so it is not on the California Public Utilities Commission's net-billing tariff (the framework people call NEM 3.0) that governs PG&E and the other investor-owned utilities. SMUD sets its own solar-and-storage rate, runs its own interconnection process, and offers SolarShares — a community-solar subscription that, where it qualifies, may satisfy the Title 24 PV obligation without a single panel on your roof (confirm eligibility with SMUD). In PG&E's foothill territory you're on the CPUC net-billing structure, and the payback math on a rooftop system looks different.

The practical takeaway: the Title 24 requirement is the same statewide, but how you satisfy it most cost-effectively, and what the power is worth afterward, depends on which side of the SMUD/PG&E line your parcel sits. Confirm interconnection and current solar-program terms with your specific utility before you finalize the design.

See also:ADU rules in El Dorado County — PG&E foothill territory

Sacramento-region local considerations that change the answer

Climate zone and utility are only the start. Several conditions specific to this region push a detached ADU toward — or away from — a rooftop array:

The through-line: the code is uniform, but the roof, the trees, the historic overlay, and the utility on your street are not. A builder who has pulled these permits reads all of them before promising you a system size or a price.

• Mature tree canopy in central-city neighborhoods: the elms and shade trees over Land Park, East Sacramento, Curtis Park, and Boulevard Park routinely limit solar access, which can trigger the code's reduced-system or exemption path on a detached ADU.
• Historic districts: in preservation-reviewed neighborhoods like Boulevard Park and Poverty Ridge, visible roof-mounted panels can draw design-review scrutiny from City of Sacramento Preservation — worth confirming before you commit to a street-facing array.
• Foothill lots: sloped, sometimes rocky parcels in El Dorado Hills, Auburn, Cameron Park, Loomis, and Granite Bay may favor a ground-mount or an array on a better-oriented roof plane, and these sit in PG&E's climate zones rather than SMUD's Zone 12.
• Narrow infill lots: tight Midtown and Curtis Park lots can leave an ADU roof partially shaded by the main house or a neighbor, feeding into the solar-access exception.
• Permit authority varies: the City of Sacramento's Community Development Department, Sacramento County (Carmichael, Fair Oaks, Orangevale), Placer County Building, El Dorado County Planning & Building, and West Sacramento Community Development each check Title 24 compliance — so the reviewer, not just the code, differs by address.

What some contractors get wrong (and shortcuts to avoid)

Solar is one of the easiest line items to fumble on an ADU bid, and the mistakes cut both ways — some contractors add cost you don't owe, others hide cost you do.

The clean way to handle this is to have your Title 24 energy compliance run during design, before the bid is finalized, so the PV requirement (or the exemption) is a known number instead of a change order.

• Assuming every ADU needs panels: a bidder who quotes solar on a garage conversion or an interior Junior ADU is charging you for a requirement that alterations don't carry.
• Assuming no ADU needs panels: the opposite lowball — leaving PV off a detached-ADU quote so the number looks competitive, then billing it as a change order once plan check flags it.
• Guessing the system size: PV size comes out of the compliance software from conditioned floor area and climate zone, not a rule of thumb. A guessed size fails plan check or over-buys hardware.
• Ignoring the exceptions: not checking shading, battery credit, or a community-solar path can mean paying full price for panels the code would have let you reduce or skip.
• Treating a government incentive as a fixed discount: rebate and interconnection terms change and differ by utility — verify current amounts with SMUD or PG&E rather than trusting a number written into a bid.
• Skipping the registered compliance document: the building department needs a signed Title 24 report; a bid that has no line for energy compliance is a bid that hasn't done this work yet.

How Upside handles Title 24 solar on your ADU

As a licensed California design-build contractor, we run Title 24 Part 6 compliance in-house during design — not after you've signed. Before we hand you a fixed price, our energy consultant classifies the project (new detached dwelling vs. addition vs. conversion), runs the conditioned floor area and your parcel's climate zone through Energy Commission-approved software, and tells you exactly whether a PV system is required and how big it needs to be.

If it is required, we check the exceptions before defaulting to a full rooftop array: solar access on your specific roof, a battery credit, a ground-mount on a foothill lot, or — in SMUD territory — whether SolarShares is a cleaner path than panels. We keep permits and engineering under one roof, so the Title 24 document, the electrical design, and the building-department submittal move together instead of getting handed between subs. On a City of Sacramento pre-approved plan set, that coordination is part of why plan check can move faster than a fully custom submittal.

You get one number that already accounts for solar — or a clear reason you don't owe it — instead of a surprise line item after the permit is in review.

See also:Talk through your ADU and its solar requirement — we scope Title 24 before you sign