Do ADUs Need Solar Panels in California? Title 24 Rules Explained

If you are planning an ADU in Los Angeles, solar is one of the first code questions that comes up. California's Energy Code, known as Title 24, has required solar photovoltaic systems on new residential construction since January 1, 2020, and that rule reaches many ADU projects.

The short answer is that newly constructed detached ADUs generally need solar panels, while conversions of existing space generally do not. The details decide your budget, so we break down exactly where your project lands before a single permit is filed.

Which ADUs require solar under Title 24

The California Energy Commission treats a newly built ADU as new residential construction. That places it under the same solar mandate that applies to a new single family home.

Your ADU will typically require a solar PV system if it falls into any of these categories:

• A detached ADU built from the ground up in your backyard
• A new attached ADU that adds newly conditioned square footage to your home
• A two story ADU or an ADU built above a new garage structure
• A prefab or modular ADU placed on a new foundation, since installation still counts as new construction

The system must be sized to offset the expected annual electricity use of the new dwelling. For most Los Angeles ADUs between 400 and 1,200 square feet, that works out to a system in the range of 1.5 to 3 kW, which is far smaller than a typical whole house array.

Which ADUs are exempt from the solar mandate

Conversions are the big exception, and they are exactly the projects where Los Angeles homeowners save the most. If you are converting space that already exists, the state does not treat it as new construction for the solar requirement.

Common exempt projects include:

• A garage conversion ADU using the existing garage footprint
• A junior ADU (JADU) carved out of space inside your existing home
• Basement, attic, or storage room conversions into a legal dwelling
• Legalizing an existing unpermitted unit through the city's ADU legalization pathway

Title 24 also allows exceptions even for new construction in specific situations. If your roof gets heavy shade from protected trees or neighboring structures, or the usable roof area is too small for a code minimum system, the energy consultant can document an exception in the Title 24 report.

How Los Angeles handles ADU solar compliance

Compliance is proven in the Title 24 energy report that gets submitted with your plans. LADBS will not issue a building permit for a new detached ADU without energy documentation showing either a compliant PV system or a valid exception.

There are also two alternate paths worth knowing. Panels can be installed on the main house roof instead of the ADU roof if that placement performs better, and adding a battery storage system can reduce the required PV size through compliance credits in the energy calculation.

What solar adds to your ADU budget

For a typical Los Angeles ADU, the mandated solar system is a smaller line item than most owners expect. Planning for it early keeps it from becoming a surprise change order.

Realistic numbers for an ADU sized system in Los Angeles:

• A 1.5 to 2 kW system usually runs about $4,500 to $7,500 installed
• A 3 kW system for a larger two story ADU runs about $8,000 to $11,000
• The federal Residential Clean Energy Credit currently returns 30 percent of the cost at tax time
• Monthly electric savings of $40 to $90 are typical for ADU tenants or family members using the unit

Set against a total ADU construction budget, solar is usually 2 to 4 percent of the project. It also gets folded into ADU financing, so it is spread across the same loan rather than paid out of pocket.

Why solar makes sense even when it is not required

Plenty of our garage conversion clients add a small PV system voluntarily, and the math usually supports it. A rental ADU with solar carries lower utility bills, which supports stronger rent and fewer vacancy gaps.

There is a second benefit specific to Los Angeles. If the ADU meter stays tied to the main house, panels sized for the ADU offset the whole property's usage under NEM billing, which shortens the payback period on the system to roughly six to nine years at current LADWP and SCE rates.

How we handle the solar piece

Our design and permits team runs the Title 24 energy calculation during the design phase, not after plan check comments come back. That means the PV size, panel placement, and any exception documentation are settled before submittal, which protects your permit timeline.

During ADU construction, the solar install is scheduled alongside roofing and electrical rough in so there is one inspection sequence instead of two. If your project is a conversion and exempt, we will tell you plainly and show the numbers for adding solar anyway, with zero pressure either way.

Getting your ADU project solar ready

The solar mandate is not a reason to delay an ADU. It is a fixed, predictable cost on new builds and a non issue on conversions, and every path through it is well mapped in Los Angeles.

Start with our free 48 hour lot check. We will confirm whether your project needs solar, what size system Title 24 will require, and what the full build will cost with the panels included, so you make the decision with real numbers in front of you.

This article summarizes California Energy Code requirements as applied in Los Angeles in 2026 and is not legal or engineering advice. Your Title 24 report governs the final requirement for your parcel.

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Sources and official references

Every rule, limit and code reference on this page comes from the sources below. Verify anything before you sign a contract.

• California Energy Commission building energy efficiency standards
• California Building Standards Commission code library
• Los Angeles Department of Building and Safety
• US Department of Energy residential clean energy credit