ADU Solar Exceptions and Exemptions Under the 2025 Energy Code
A new detached ADU needs solar unless an exception applies, while attached ADUs, garage conversions and conversions of existing rooms need none at all. For a one-unit ADU the 1.8 kWdc exception does most of the work: it covers floor areas up to about 1,265 square feet in climate zone 5 but only about 212 in zone 15.
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Section 150.1(c)14 reaches newly constructed buildings. The Energy Commission says an attached ADU is an addition and needs no solar PV. HCD adds that an ADU built inside existing space, or by turning a detached non-residential building into housing, is outside the requirement too. See the attached ADU page and the garage conversion page.
Exception 2 by floor area
The requirement is the smaller of Equation 150.1-C and the solar access roof area times 18 W per square foot (14 on a low slope). For one dwelling unit the equation is floor area times factor A, over 1,000, plus factor B from Table 150.1-C. Exception 2 applies when the result is under 1.8 kWdc, which on an unshaded roof means below about:
- Climate zone 5: 1,265 square feet
- Zone 1: 668
- Zone 12: 653
- Zone 11: 431
- Zone 13: 324
- Zone 15: 212
The equation counts the building, not each ADU, so a duplex of ADUs adds factor B twice.
Roof-side exceptions in practice
The manual's Example 9-8c: a duplex of ADUs in zone 1, 500 square feet in all, has a low-slope roof left with 125 square feet of usable area after tree shade and fire clearances. The equation gives 2.94 kW, the roof 125 times 14, or 1.75 kW. The smaller figure is under 1.8, so no PV is required, on the strength of an approved shading study.
The other routes
Exceptions 1, 3, 4 and 5 (a small steep roof, snow load, pre-2020 planning approval, a battery) are set out on the solar exemptions page. The manual also notes PV is not needed when the design complies without it on the performance path.
The common mistake
Treating a small ADU as exempt because it is small. A 400 square foot unit in zone 13 calculates to 1.87 kWdc. The arithmetic is on the solar system size page, the basic rule on ADU solar, and panel placement on adding panels to the main house. Orders start on the ADU page.
Common Title 24 Questions
- Do ADUs need Title 24 in California?
- What plans are needed for an ADU Title 24 report?
- How much does an ADU Title 24 report cost?
- How long does an ADU Title 24 report take?
- Does a garage conversion ADU need Title 24?
- Does a JADU need a Title 24 report?
Frequently Asked Questions
It depends on the calculated size, not the floor area alone. In climate zone 5 a one-unit ADU under about 1,265 square feet calculates below 1.8 kWdc, while a 400 square foot unit in zone 13 calculates to 1.87 kWdc.
No. A conversion is an addition or an alteration, and Exception 6 to Section 150.2(a) states that PV is not required for additions.
Yes. The compliance manual says solar is required unless compliance can be achieved without PV using the performance path.
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View all ADU and JADU guides → · Permits and Compliance · Title 24 guide