California ADU Law - September 2020 Updated Guidance
Update August 2022: There is a new HCD handbook. All the links in this article now go to the NEW handbook dated July 2022
Read the new guidance about the state-wide ADU laws in California.
The HCD released a handbook in September 2020 that clarifies how ADU regulations interact at a local and state level, and how different parts of the Accessory Dwelling Unit laws are supposed to be interpreted at the city and county level.
If you don’t have time to read it all, you can read this article or watch the accompanying youtube video with my key takeaways.
If you would like any help researching ADU laws or developing your own ADU, please consider sharing your project with me. I’m not a lawyer so I don’t offer legal advice, but I am eager to help as many Californians develop ADUs as possible – and I read ADU legal updates for fun. So there’s that…
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!
Key Concepts in the Updated Guidance
The updated guidance introduces the phrase “Statewide Exemption ADU” that explains how big an ADU can be in California, and what kind of limits can and cannot be imposed. I think this is a much clearer explanation which you can read about below.
The handbook also defines “proportionately” and “objective”, two important terms in the state code which are key to enforcing the provisions of AB 68 and other state laws promoting ADU development.
Lastly there are a number of important miscellaneous clarifications that I’ve summarized at the bottom of this article. These include school district impact fees, historic districts, coastal zone LCPs, JADU garage conversions, JADU bump outs, multifamily dwellings, and enforcement.
How big can an ADU be in California?
This common question has a complicated answer, but the new guidance makes the ADU rules much easier to understand.
If your property is an a city or county with no ADU ordinance…
A detached ADU can be up to 1200 square feet.
This is in the state code because of the new ADU laws that went into effect in January 2020.
If your property is in a city or county with an ADU ordinance…
The local ordinances can be very complicated.
Local jurisdictions can impose size requirements (those are pretty easy to understand), and they can impose other more complicated requirements that only apply under specific conditions.
No matter how complicated things get, there are two important things to remember:
1. Statewide Exemption ADU Rules
The HCD says you can build a “statewide exemption ADU” up to 800 square feet and you won’t be subject to lot coverage, floor area ratio (FAR), open space or minimum lot size requirements.
Here’s the HCD’s definition of a statewide exemption ADU:
What is a Statewide Exemption ADU?
A statewide exemption ADU is an ADU of up to 800 square feet, 16 foot in height and with 4-foot side and rear yard setbacks. ADU law requires that no lot coverage, floor area ratio, open space, or minimum lot size will preclude the construction of a statewide exemption ADU. Further, ADU law allows the construction of a detached new construction statewide exemption ADU to be combined with a JADU within any zone allowing residential or mixed uses regardless of zoning and development standards imposed in an ordinance. See more discussion below.
So if you’re under 800 square feet, you can avoid many kinds of ADU restrictions according to the HCD guidance.
2. Accessory Structures are not subject to the same rules
And if you’re converting an existing accessory structure (or a portion of the existing primary residence) to an ADU, the HCD says you are not subject to size requirements.
Here’s the HCD’s explanation of that concept:
The conversion of an existing accessory structure or a portion of the existing primary residence to an ADU is not subject to size requirements. For example, an existing 3,000 square foot barn converted to an ADU would not be subject to the size requirements, regardless if a local government has an adopted ordinance. Should an applicant want to expand an accessory structure to create an ADU beyond 150 square feet, this ADU would be subject to the size maximums outlined in state ADU law, or the local agency’s adopted ordinance.
So if you’ve got a 3000 square foot barn, you’ve got a big development opportunity on your hands!
More complicated ADU Law in California
The state code also says maximum square footage requirements for ADUs can be no smaller than 850 square feet or 1000 square feet for ADUs with 2 or more bedrooms.
While this is true, cities can impose other restrictions on ADUs above 800 square feet that may prevent you from building up to these maximum size limits.
For example, a city might allow homeowners to build ADUs up to 1000 square feet, but the city imposes a lot coverage or Floor Area Ratio requirement for ADUs above 800 square feet which makes it impossible for a particular homeowner to build over 800 square feet.
Can a detached ADU be bigger than 1200 square feet?
There are a few ways you might be able to get a permit for a detached ADU above 1200 square feet.
Even though the state ADU law says “The total floor area for a detached accessory dwelling unit shall not exceed 1,200 square feet”, your city or county can pass a law that allows you to build ADUs larger than that.
Additionally, if you’re converting an accessory structure like a 3000 square foot barn, the HCD says you should not be subject to ADU size restrictions.
Lastly, you could apply for a discretionary permit. These ADU laws are designed for homeowners to obtain non-discretionary, ministerial permits, sometimes referred to as “by right”.
That said, you can propose a project that goes outside the guidelines set forth in the state law and local ordinances. You may have to go through a review process with your city or county like a planning review.
Here’s a video about a planning review where a homeowner wanted to obtain a permit for a tiny ADU that is actually below the minimum size requirement. This is an approach you may want to consider if your local planning department is friendly to ADU development.
When ADU Law says “Proportionately” or “Objective”…
Very important parts of the ADU laws that went into effect in January 2020 rely on the words “proportionately” and “objective” so the HCD has clarified what those terms mean.
“Proportionately” in ADU Law
Before this clarification, it wasn’t always clear what the impact fees should be proportional to or what ratio to use.
“Proportionately” is some amount that corresponds to a total amount, in this case, an impact fee for a single-family dwelling. For example, a 2,000 square foot primary dwelling with a proposed 1,000 square foot ADU could result in 50 percent of the impact fee that would be charged for a new primary dwelling on the same site. In all cases, the impact fee for the ADU must be less than the primary dwelling. Otherwise, the fee is not calculated proportionately. When utilizing proportions, careful consideration should be given to the impacts on costs, feasibility, and ultimately, the creation of ADUs. In the case of the example above, anything greater than 50 percent of the primary dwelling could be considered a constraint on the development of ADUs.
This still leaves me with some questions since impact fees are not always leveed on a “per square foot” basis.
But it does bring some clarity to the intention of the law.
For example: Let’s say my property is in a city that would charge me $5,000 in impact fees to build a 2,000 square foot house, and I propose to build a 1,000 square foot ADU.
In this example, I would expect the city to charge me about $2,500 or 50% of the amount that I’d be charged for building a 2,000 square foot home.
Impact Fees under 750 square feet
If I build an ADU under 750 square feet, I should not be charged any impact fees according to state law, with the possible exception of School District impact fees (this is addressed in its own section further down in the article).
But as soon as I propose a 750+ square foot ADU, I can be charged a proportional impact fee for the full size of the ADU.
So if you’re planning a 751 square foot ADU, that extra square foot might be costing you a LOT of money and you may want to consider ways to get down to 749 square feet.
The word proportionate comes up again when trying to calculate water and sewer connection fees.
ADUs converted from existing space and JADUs shall not be considered by a local agency, special district or water corporation to be a new residential use for purposes of calculating connection fees or capacity charges for utilities, unless constructed with a new single-family dwelling. The connection fee or capacity charge shall be proportionate to the burden of the proposed ADU, based on its square footage or plumbing fixtures as compared to the primary dwelling. State ADU law does not cover monthly charge fees. (Gov. Code, § 65852.2, subd. (f)(2)(A))
If your local water district or water corporation is trying to charge you a connection fee that you don’t think is in line with the state law, you should contact them directly - this is often separate entity, independent from the planning department or building department.
“Objective” in ADU Law
“Objective zoning standards” and “objective design review standards” mean standards that involve no personal or subjective judgment by a public official and are uniformly verifiable by reference to an external and uniform benchmark or criterion available and knowable by both the development applicant or proponent and the public official prior to submittal. Gov Code § 65913.4, subd. (a)(5)
This one is a bit more complicated.
Important note: I’m not a lawyer and I don’t give legal advice… what I can do is provide fictional examples of how I might apply the definition above to a local ordinance to question whether it could be argued to be objective or not.
The way I think about it, an ordinance that says “ADUs must be in line with the design and character of the primary residence in the eyes of the planning commission and neighbors” would probably not pass the test for objective standards.
The opinions of the planning commission members and your neighbors is not something I can know before applying for the permit.
It relies too much on their subjective opinions.
That said, if the ordinance were worded along the lines of “ADUs must use the same exterior finish, material, and color as the primary residence” then that may pass the test for objective standards.
As a homeowner, I can match the exterior finish, material and color - there’s an objective and verifiable standard that keeps the whole process ministerial.
Other ADU Rules the HCD Clarified
Does California ADU law stop school districts from charging development impact fees?
While the state code clearly says that local agencies cannot charge development impact fees for ADUs below 750 square feet in size, school districts can still levy impact fees on ADUs above 500 square feet according to the HCD handbook.
Can school districts charge impact fees?
Yes. School districts are authorized but do not have to levy impact fees for ADUs greater than 500 square feet pursuant to Section 17620 of the Education Code. ADUs less than 500 square feet are not subject to school impact fees. Local agencies are encouraged to coordinate with school districts to carefully weigh the importance of promoting ADUs, ensuring appropriate nexus studies and appropriate fees to facilitate construction or reconstruction of adequate school facilities.
What types of fees are considered impact fees?
Impact fees charged for the construction of ADUs must be determined in accordance with the Mitigation Fee Act and generally include any monetary exaction that is charged by a local agency in connection with the approval of an ADU, including impact fees, for the purpose of defraying all or a portion of the cost of public facilities relating to the ADU. A local agency, special district or water corporation shall not consider ADUs as a new residential use for the purposes of calculating connection fees or capacity charges for utilities, including water and sewer services. However, these provisions do not apply to ADUs that are constructed concurrently with a new single-family home (Gov. Code, § 65852.2, subd. (f) and Government Code § 66000)
Can you build ADUs in Historic Districts and Coastal Zones?
Historic Districts
Can I build an ADU in a historic district, or if the primary residence is subject to historic preservation?
Yes. ADUs are allowed within a historic district, and on lots where the primary residence is subject to historic preservation. State ADU law allows for a local agency to impose standards that prevent adverse impacts on any real property that is listed in the California Register of Historic Resources. However, these standards do not apply to ADUs proposed pursuant to Gov. Code § 65852.2, subd. (e). 9
As with non-historic resources, a jurisdiction may impose objective and ministerial standards that are sufficiently objective to be reviewed ministerially and do not unduly burden the creation of ADUs. Jurisdictions are encouraged to incorporate these standards into their ordinance and submit these standards along with their ordinance to HCD. (Gov. Code, § 65852.2, subd. (a)(1)(B)(i) & (a)(5))
Coastal Zone
The way I think about this is that the HCD is explicitly saying that ADUs can be built in coastal zone, as long as they follow all the rules in the coastal zone. And then the HCD is encouraging the LCPs (Local Coastal Programs) to be lenient and referring to a California Coastal Commission 2020 memo that encourages the same.
Do the new ADU laws apply to jurisdictions located in the Coastal Zone?
Yes. ADU laws apply to jurisdictions in the Coastal Zone, but do not necessarily alter or lessen the effect or application of Coastal Act resource protection policies. - (Gov. Code, § 65852.22, subd. (l)).Coastal localities should seek to harmonize the goals of protecting coastal resources and addressing housing needs of Californians. For example, where appropriate, localities should amend Local Coastal Programs for California Coastal Commission review to comply with the California Coastal Act and new ADU laws. For more information, see the California Coastal Commission 2020 Memo and reach out to the locality’s local Coastal Commission district office.
That memo has a lot of ways for LCPs to be nice to you. They can say your ADU or JADU doesn’t require a CDP. They can also issue a CDP waiver.
I’ll write about coastal zones separately since this comes up a lot for our subscribers, especially in southern California. But in the meantime, I highly encourage you to download and read the 6 page memo and contact your local LCP asking them to decide if your proposed project requires a CDP or not.
Can you convert a garage into a JADU?
A garage attached to the proposed or existing single-family residence can be converted into a JADU according to the HCD’s updated guidance.
The JADU may be created within the walls of the proposed or existing single-family residence, including attached garages, as attached garages are considered within the walls of the existing single-family residence...(Gov. Code, § 65852.22, subd. (a)(1))
Can you convert detached accessory structures to JADUs?
Not according to the HCD’s guidance on the state law.
Your local planning department can choose to be less restrictive than the state guidance and allow a conversion of an accessory structure to be permitted as a JADU, but there is no requirement in the state code to do so.
That said, you can convert an accessory structure as a conventional ADU (not a Junior). Here’s the HCD guidance on that:
Can I convert my accessory structure into an ADU?
Yes. The conversion of garages, sheds, barns, and other existing accessory structures, either attached or detached from the primary dwelling, into ADUs is permitted and promoted through the state ADU law. These conversions of accessory structures are not subject to any additional development standard, such as unit size, height, and lot coverage requirements, and shall be from existing space that can be made safe under Building and Safety Codes. A local agency should not set limits on when the structure was created, and the structure must meet standards for Health & Safety. Finally, local governments may also consider the conversion of illegal existing space and could consider alternative building standards to facilitate the conversion of existing illegal space to minimum life and safety standards.
Can you add 150 sq ft for a JADU entrance?
Not according to the HCD’s guidance on the state law.
Are JADUs allowed to be increased up to 150 square feet when created within an existing structure?
No. Only ADUs are allowed to add up to 150 square feet “beyond the physical dimensions of the existing accessory structure” to provide for ingress. (Gov. Code, § 65852.2, subd. (e)(1)(A)(i).)
This provision extends only to ADUs and excludes JADUs. A JADU is required to be created within the single-family residence.
That said, the state law literally says “(i) The accessory dwelling unit or junior accessory dwelling unit is within the proposed space of a single-family dwelling or existing space of a single-family dwelling or accessory structure and may include an expansion of not more than 150 square feet beyond the same physical dimensions as the existing accessory structure. An expansion beyond the physical dimensions of the existing accessory structure shall be limited to accommodating ingress and egress.“
As always, a conversation with your local planning department might be the best way to clear up how they want to interpret the state code and local ordinances.
What is considered a multifamily dwelling?
If you have a lot with a multifamily dwelling on it, there are different rules about what you can build (and you can probably build more ADUs).
But some local jurisdictions have had different views on what counts as a multifamily dwelling.
The HCD guidance below suggests that if a single structure has two or more attached dwellings, it’s a multifamily dwelling.
On the other hand, if you have multiple detached single-unit dwellings on the same lot, you do not have a multifamily dwelling for the purposes of state ADU law.
What is considered a multifamily dwelling?
For the purposes of state ADU law, a structure with two or more attached dwellings on a single lot is considered a multifamily dwelling structure. Multiple detached single-unit dwellings on the same lot are not considered multifamily dwellings for the purposes of state ADU law.
How are these rules enforced?
The HCD ultimately has enforcement authority over all these ADU ordinances. That’s why their guidance matters!
Does HCD have enforcement authority over ADU ordinances?
Yes. After adoption of the ordinance, HCD may review and submit written findings to the local agency as to whether the ordinance complies with state ADU law. If the local agency’s ordinance does not comply, HCD must provide a reasonable time, no longer than 30 days, for the local agency to respond, and the local agency shall consider HCD’s findings to amend the ordinance to become compliant. If a local agency does not make changes and implements an ordinance that is not compliant with state law, HCD may refer the matter to the Attorney General.
In addition, HCD may review, adopt, amend, or repeal guidelines to implement uniform standards or criteria that supplement or clarify ADU law.
Please share your project with me for more free resources
If you found this article helpful, please consider sharing your project with me so that I can help you build your ADU.
The local ordinances can change any month, and the interpretation of these ordinances is constantly evolving - so you’ll get a lot of benefit from sharing your project with an ADU specialist!