ADU Solar Requirements in California - Do you need Solar Panels on your Accessory Dwelling Unit?
California has some complicated energy requirements, so a lot of homeowners ask us what their solar requirements are when they are planning and budgeting a potential Accessory Dwelling Unit (ADU).
Do all ADUs permitted in California after January 1, 2020 need to have solar panels?
According to Title 24, newly built, non-manufactured, detached ADUs will generally need to install solar panels if the local agency is enforcing the prescriptive energy requirements in California’s state code.
On the other hand, manufactured units, garage conversions, and attached ADUs generally won’t be required to install solar panels.
If you’re converting an existing part of your home, converting an accessory structure, or adding an attached ADU to an existing part of the home or accessory structure, you probably won’t need to install solar panels.
California’s 2020 Solar Mandate requires the installation of solar panels like these on most new detached home building in the state
There are also a handful of reasons some homeowners may not need to install ADU solar panels even if they are building a detached new non-manufactured unit.
And finally, homeowners may avoid installing solar panels if it’s possible for them to meet performance standards for compliance instead of prescriptive standards.
We’ll try to explain all of this as simply as possible in this article and accompanying video. And after that, I’ll add that you might want to install solar panels even if you find that they’re not legally required in your case.
As always, this is not legal advice - the information on this website is presented as general information. You should speak to a licensed professional in your jurisdiction and work with local agencies on your project!
Title 24 Solar Requirements in California
According to updated guidance from the HCD (California Department of Housing and Community Development), newly constructed ADUs are subject to the Energy Code requirement to provide solar panels if the unit is:
Newly constructed
Non-manufactured (manufactured units are subject to Title 25, not Title 24)
Detached ADU
Here’s the exact wording about Title 24 ADU requirements, from the ADU Handbook the HCD released in September 2020:
Are solar panels required for new construction ADUs?
Yes, newly constructed ADUs are subject to the Energy Code requirement to provide solar panels if the unit(s) is a newly constructed, non-manufactured, detached ADU. Per the California Energy Commission (CEC), the panels can be installed on the ADU or on the primary dwelling unit. ADUs that are constructed within existing space, or as an addition to existing homes, including detached additions where an existing detached building is converted from non-residential to residential space, are not subject to the Energy Code requirement to provide solar panels.
Please refer to the CEC on this matter. For more information, see the CEC’s website www.energy.ca.gov. You may email your questions to: title24@energy.ca.gov, or contact the Energy Standards Hotline at 800- 772-3300. CEC memos can also be found on HCD’s website at https://www.hcd.ca.gov/policy-research/AccessoryDwellingUnits.shtml
The CEC (California Energy Commission) has also published guidance in January 2020 that specifically talks about Accessory Dwelling Unit solar panel requirements and some exemptions to the state’s PV mandate.
Here’s the excerpt from page 4 of issue 129 of the CEC’s guidance:
The 2019 Energy Code PV system prescriptive requirements under Section 150.1(c)14 apply only to newly constructed detached accessory dwelling units (ADUs) for which the permit application was submitted on or after January 1, 2020. Smaller ADUs will require smaller PV systems, or may be exempt from the PV system requirements if they meet Exception 1 to Section 150.1(c)14:
• 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, including but not limited to trees, hills, and adjacent structures. The effective annual solar access shall be 70 percent or greater of the output of an unshaded PV array on an annual basis.
The PV system can be installed on the ADU, or on the main house. In the event that panels are added to an existing PV system to satisfy the PV system requirements for the ADU, those additional panels must be part of the ADU’s permit application. The PV system requirements do not apply to alterations or additions to existing homes, including detached additions where an existing detached building is converted from unconditioned to conditioned space (this is an addition per the Energy Code definitions).
Note: Energy Code requirements, including the PV requirements, do not apply to mobile home ADUs, which are subject to Title 25, not Title 24.
Riveting reading, I know…
Title 24 exemptions to solar requirements
In a nutshell it seems like they’re saying:
Manufactured units subject to Title 25 may not need to meet Title 24 requirements
Attached ADUs are “additions” so Title 24 doesn’t require PV installation
Conversion ADUs are “additions” so Title 24 doesn’t require PV installation
Even detached conversions are “additions” so Title 24 doesn’t require PV installation
There are conditions where you can be exempt because you don’t have a large enough surface area with unshaded solar access
“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, including but not limited to trees, hills, and adjacent structures. The effective annual solar access shall be 70 percent or greater of the output of an unshaded PV array on an annual basis.“
You can meet the solar requirements by adding panels to the primary house or elsewhere on the property
You can meet the solar requirements by adding panels to an existing array
As always, enforcement is up to local agencies - and I don’t offer legal advice because I’m not a lawyer.
Hopefully, this summary of the documents I’ve shared from the HCD and CEC give an accurate idea of the different conversations you can have with your local planning and building department to get to the best outcome for your potential ADU projects.
Can the city or county have different standards than the state?
Yes, cities and counties can adopt different standards than the state (they are supposed to only adopt more restrictive standards).
For example, “The State Housing Law in HSC Section 17958.5 allows local amendments to Title 24 requirements applicable to the construction of single- and multiple-family dwellings, hotels, motels and lodging houses. “
Here is a video from the California Building Standards Code (CBSC) about how that process works.
Even though it seems like local ordinances should only ever vary in that they’re stricter than the state code, I’ve heard experienced builders say that sometimes local enforcement is more lenient.
I’ll avoid any specific examples because I don’t want to get anybody in trouble (including me!), but it’s something I wanted to note.
This might also happen in cases where one part of the code gives a local agency more power over adoption and enforcement of local amendments like rules about Emergency Rulemaking and Emergency Housing, but these exceptions shouldn’t generally apply to most homeowners in California.
California solar requirements vary by climate and region
Furthermore, the PV requirements vary depending on where you are. The standards are different depending on where your property is located.
Part 6 of Title 24 (the law that covers low-rise residential buildings) has different standards in different parts of the state, based on climate zones.
You can also measure compliance with two different methods (performance method or prescriptive method) - while the prescriptive method dictates specific things like “You have to have solar panels”, the performance method works by calculating the home’s energy efficiency and then verifying it. I don’t have a lot of experience with this so I can’t give more specific information, but I can imagine that there are ways to get creative with this. For example, a lot of subscribers have asked me about “off-grid” ADUs and I have to imagine that some of the off-grid solutions could meet net zero energy requirements even without solar panels (because they’re using so little energy, for example). I’ll publish more on this when I’ve gathered more information.
Why you might want solar panels anyway
The whole time I wrote this article, I felt a bit torn because I think that installing solar panels is often a very smart choice.
There are a number of reasons homeowners ask about solar requirements. And it’s very smart to do your research about the law.
Once you’ve done your research, I would strongly encourage you to consider solar energy in your future project.
Installing solar panels involves a sizable one time investment, but you can save a lot of money in the long run by building an energy efficient ADU.
You might also be independent from the PG&E power shut offs we’ve experienced in the past few years, depending on the conditions of your property and your installation.
You can also explore financing options for solar panel installation or alternatives where solar providers install panels at no immediate cash cost to you.
Anyway, most people aren’t looking for a speech about the environment so I’ll spare you the lecture.
Suffice it to say that whether you’re concerned with the environmental impact of your home, or the potential savings, solar panel installations are often a great investment.
Useful links:
The actual CA Title 24 code is available online: https://www.dgs.ca.gov/BSC/Codes
At the time of publishing this article, the Jan 1 2020 update to Title 29’s Triennial Edition is available here: https://cdn-web.iccsafe.org/wp-content/uploads/errata_central/2019-California-Administrative-Code-Part-1-Errata-eff.-January-2020_COMPLETE.pdf
And part 6 on California Energy Code, containing the section that people think of as California solar panel law, is available here: https://cdn-web.iccsafe.org/wp-content/uploads/errata_central/2019-CA-Energy-Code-Part-6-Errata-eff.-January-2020_COMPLETE.pdf
The HCD Handbook cited at the beginning of this article: https://www.how-to-adu.com/s/ADU-TA-Handbook-Final.pdf
The CEC guidance on ADUs cited at the beginning of this article: https://www.hcd.ca.gov/policy-research/docs/cec-blueprint-newsletter-129.pdf
Alternative link: http://www.title-24.com/docs/2019_adu.pdf
A very useful guide to the entirety of Title 24 - this is more exhaustive and does not limit itself to the small section on photovoltaic requirements: https://www.library.ca.gov/content/pdf/law/GuideToTitle24.pdf