Do ADUs Need Solar Panels?

Does the CA Title 24 solar requirement apply to ADUs? Learn the answer to this and many more related questions in our blog post on solar energy for ADUs.

Last updated 
April 14, 2023
Do ADUs Need Solar Panels?

Do ADUs Need Solar Panels?

Many California homeowners planning to build an accessory dwelling unit have questions about Title 24’s solar energy requirements and whether they apply to ADUs. In this post, we’ll walk you through green energy guidelines in the golden state and how they apply to ADU construction, as well as the benefits of adding solar to your project.

ADU Solar Q&A

Listed below are some of the common questions regarding solar requirements for California ADUs.

Q: What is Title 24?

A: California’s Title 24 is a set of energy efficiency standards for new buildings. Title 24 was designed to promote sustainability as part of California’s goal of becoming a 100% clean energy state in the near(ish) future.

One of Title 24’s stipulations is that new residential buildings must include a photovoltaic (solar energy) system with an electrical output that’s equal to the dwelling’s annual electrical usage. In other words, you have to make as much energy as you consume.

Learn more about recent changes to Title 24 in this blog post.

Q: Do the Title 24 solar requirements apply to ADUs?

A: Yes, but not all ADUs. Solar panels are required for most newly constructed, non-manufactured, detached ADUs. So if you’re building an in-law unit from the ground up, it probably needs to be powered by solar energy.

However, if the minimum PV system size specified by Title 24 (section 150.1(c)14) is smaller than 1.8 kW, the solar requirement does not apply.

To determine the size of your ADU’s PV system, you’ll need to know your climate zone (if you live in Los Angeles, your climate zone is likely 10, 9, 8, or 6). Once you know your climate zone, refer to the calculation and tables under Title 24 150.1(c)14 to find your unit’s PV system size.

According to Title 24, here are the maximum ADU sizes in LA climate zones before a PV system is needed:

Zone 10: 606.06 net square feet

Zone 9: 701.46 net square feet

Zone 8: 716.72 net square feet

Zone 6: 942.76 net square feet

There are some other cases in which the solar requirement does not apply. Manufactured (prefab) units and attached ADUs are exempt. Garage conversion units do not require solar panels either, as they are technically classified as renovations.

Q: How many solar panels do I need?

A: If your planned ADU requires solar energy, you’ll need a minimum of 8 panels. And if your unit exceeds 1,000 square feet, you’ll likely need more.

Q: How much does it cost to add solar to an ADU?

A: Solar panels and installation adds about $12-18K to the ADU’s total cost. But between the tax rebate and energy savings—as well as improved sustainability—it’s a worthwhile investment.

Q: Will ADU construction take longer if I add solar?

A: No, the solar panel installation will not extend the construction timeline for your ADU.

Q: Do the solar panels have to go on the roof of the ADU?

A: Nope! They can go on the roof of the main house instead. And while the roof is the most popular choice for solar panel placement, it’s not the only option. You’re free to install solar panels in a different location on your property, provided there’s enough space and sunlight is unobstructed.

Q: Should I add solar panels even if I don't need to?

A: Since you're already financing an ADU that will add value to your home and bring in passive income, we encourage you to bundle in solar as well. Yes it’s an added expense, but like the rest of the ADU, it’s an investment that pays for itself. There are several compelling reasons to add passive energy to your granny flat, even if you’re not legally required to do so. Here are a few of the big ones:

Tax Rebate

Installing solar panels makes you eligible for the federal solar tax credit. **** The Inflation Reduction Act increased the solar tax rebate from 25% to 30% for projects built between 2022 and 2032.

Qualifying homeowners can claim 30% of the total installation costs as a tax rebate with no maximum.

Learn more about the program here.

Lower energy costs

Since you won’t have to pay for electricity once you’re generating your own, your energy costs will likely go down significantly.

And if you’re planning to rent out your ADU, adding solar panels is a smart move. Solar energy makes your ADU more appealing to potential renters, since you can pass the savings from your lower energy costs on to them.

Better for the environment

Solar energy is renewable, and it reduces greenhouse gasses and our dependence on fossil fuels. ADUs already have a lighter carbon footprint, so adding solar power makes your earth-friendly granny flat even friendlier.

Learn more about sustainable ADUs in this blog post.

Invest now for the future

California green energy requirements are likely to increase over the years. If you add solar energy now, you'll be ahead of the curve and can avoid having to make costly additions down the road.


Your accessory dwelling unit may or may not require solar panels, depending on the scope of your project. But even if they aren’t required, solar energy is an excellent investment for your unit and the planet.

If you’re still unsure about whether or not your project needs solar energy, Otto can help. Schedule a free consultation with Otto today, and you’ll be well on your way to the money-making, environmentally friendly, energy-efficient ADU of your dreams.

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