Is Solar Required on New California ADUs?

One of the most common ADU questions that Revival Homes customers ask us is whether solar panels are required on new California ADUs. The answer is not always cut-and-dry, which is why we’ve written this blog post to help you out.

The short answer — in California:

• A garage conversion ADU is not required to have solar.
• An attached ADU is not required to have solar.
• A detached, new construction ADU may be required to have solar, depending on its size and location.

When is a detached, new build ADU required to have solar?

• The ADU is below a minimum size, or
• The ADU is in a heavily shaded location

In either case, the state’s energy code does not require the ADU to be powered by rooftop solar panels.

Why are small detached ADUs exempted from solar?

If you’re building a small detached ADU, the energy code will likely exempt your project from solar. This is because a small ADU needs relatively little energy, and the small size of the system needed to power a relatively small ADU would make the solar array financially impractical. The California Energy Commission’s 2022 Building Energy Efficiency Standards state that no system “is required when the minimum PV system size is less than 1.8kW.” So if your ADU needs less than 1.8kW for its energy requirements, you’re not required to install panels.

How do you know if your ADU will need less than 1.8kW? This depends on the square footage of the ADU, and where the ADU is located geographically — some parts of the state are sunnier than others (for example, the same size solar system produces much more energy in Palm Springs than it does in San Francisco). 

In practice, in most parts of California, ADUs that are below 600 to 700 ‍square feet are small enough to be exempted. This useful calculator can tell you exactly how many square feet you can build in your area while remaining below the solar exemption threshold.

If my ADU is in a shady location, is it exempted from solar?

Yes — the energy code takes into account existing shade conditions of the site and makes exceptions for projects where shade would impede solar production. A 2020 memo from the CEC states, “No PV is required if the effective annual solar access is restricted to less than 80 contiguous square feet by shading from existing permanent natural or man-made barriers external to the dwelling”. So if your ADU’s roof has less than 80 square feet of largely shade-free space, your project is exempt from solar. 

If my ADU is required to be powered with rooftop solar, where can I put the solar panels – on the house or on the ADU?

Either! The California Energy Commission states that panels can be installed on either the ADU or your primary home. We’ll look at your home’s existing setup and make a recommendation for whether it makes more sense to install on your home or new ADU. For ADU projects at homes that already have rooftop solar, it’s often easiest and most cost-effective to meet the new ADU’s solar requirements by adding capacity to an existing solar array.

How much does it cost to include rooftop solar in my ADU project?

The cost of adding a solar array to your home will vary significantly depending on the size of your ADU and the type of system you decide to purchase. The typical rooftop solar system costs between $10,000 and $20,000, including installation, and many homeowners choose to finance their solar system purchase to spread the cost over time. At Revival Homes, we’ll work with you to estimate your expected solar installation cost early on in the ADU development process, helping you to keep your project on budget. 

Solar is not required for my ADU project, but I’m still interested in adding it. How do I know if rooftop solar is right for me?

You might be interested in installing solar on your ADU (or your house as well), regardless of whether it’s required. Rooftop solar has many benefits — it’s good for the planet and can save you a lot on your electricity bills. In California, the average payback period for installing rooftop solar is just over 5 years, and converting your entire home to solar can save you as much as $1,500 annually. At Revival Homes, we can help you navigate whether solar is right for you, and we partner with top-tier solar providers to ensure that you get the best deals on your solar system.

Revival Homes is here to help you.

Revival Homes is California’s one-stop ADU shop. We work with customers to navigate the many nuances of ADUs and solar energy requirements – from whether solar is required, to system size, to picking a vendor, to certifying the install. We’re here to clear up the guesswork and help you move forward with confidence on your ADU project.

Ready to get your ADU project started? Book your free consultation with our ADU experts today!

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