Energy Efficiency, Solar Requirements, and Your California ADU

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We’re often asked by customers whether they’re required to put solar panels on their new ADU. The short (and somewhat unsatisfying) answer: “it depends”.

The longer (and more satisfying) answer is complicated — California has complex regulations when it comes to energy efficiency. That’s why homeowners who are interested in building an accessory dwelling unit, or ADU, should familiarize themselves with the state’s solar requirements when planning and budgeting for their ADU project.

In this blog post, we'll discuss the energy efficiency requirements for ADU projects in California, including Title 24 of the California Energy Code. That way, you can plan and budget accordingly, and determine whether a solar panel system at your home is right for you.

What’s Title 24?

First, some background on California’s energy efficiency regulations for homes. Title 24 of the California Energy Code sets standards for energy efficiency in new buildings, to reduce energy usage and carbon emissions. The energy code is updated every three years, with the most recent changes having taken effect on January 1, 2023.

Title 24 requires most ADUs to meet specific energy efficiency standards, which includes energy-efficient lighting, HVAC systems, and other appliances, high-performance windows, high-quality insulation, and mandatory ventilation systems. Title 24 also requires some ADUs to be built with solar panels.

When do ADUs have to be built with solar panels?

Under Title 24, an ADU must include solar panels if it meets the following three conditions:

  • It’s new construction (not conversion of existing space, like a garage)
  • It’s detached (not connected to the main house)
  • It’s built using traditional stick-built construction (not modular, prefab, or manufactured)

So a newly-constructed, stick-built, detached ADU must include solar panels. A garage conversion, a modular or prefab unit, or an extension of the primary house does not have to include solar.

Here’s a simple table to illustrate when solar is required on an ADU:

Are there exceptions, or other ways to meet the solar requirement for an ADU?

Yes. If your primary house already has solar panels, and your existing system can provide enough energy for both the primary house and the ADU, then you’re good to go. If you don’t have solar, you can also put solar panels on the primary house (or on the ADU), and use those panels to power both the primary house and the ADU.

Also, if your ADU will have a particularly small roof, or is located in a heavily shaded spot on your property, you may be able to get an exemption from the solar requirement. Check with your city planning department or your architect to find out if your project qualifies for an exemption.

How much do solar panels cost?

In the Revival Homes ADU Budget Calculator, we forecast that a solar panel system costs between $10,000 to $20,000, depending on the size and location of the ADU (and therefore, its energy needs). Many solar installers offer project financing through lenders like Mosaic, to help you defray the initial cost of the solar panel system.

Can I lower my ADU’s energy costs by installing solar?

Yes — while installing a solar panel costs money up front, you can save significantly on your energy bills over the long term. Additionally, you can benefit from new tax incentives that encourage solar, like the federal government’s 30% Residential Clean Energy Credit for the purchase and installation of solar panels. For example, if you spent $10,000 on a new solar panel system, you’d get a federal income tax credit of $3,000 that you can apply the following year.

Solar panels can also ensure that you’ll have reliable electricity access even in the event of a blackout. Over the last few years, blackouts have become more common across California, particularly during the summer months.

How do I get started?

To ensure that your ADU is fully compliant with California’s energy efficiency requirements, homeowners should work with an experienced architect or design-build general contractor who’s familiar with Title 24 and with the overall ADU design and construction process. Your ADU’s plan set should include a Title 24 report, which estimates your ADU's energy usage and confirms that your plans meet California’s energy efficiency requirements for new construction.

Regardless of whether you choose to go with solar for your ADU project, our team at Revival Homes is ready to help you plan the ADU project that’s right for you. Contact us today for your free project consultation.


More information about ADUs

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