Awaiting expert review. This page covers rules that vary by state and local jurisdiction. It is kept out of search results until a qualified reviewer has checked it; the sources below are dated so you can verify each point.
Quick answer
A local ADU ordinance is the section of a city or county's zoning code that sets the rules for accessory dwelling units in that jurisdiction: where they are allowed, how big and tall they can be, setbacks, design standards and the application process.
In California an ordinance is optional but bounded: it may use objective standards only, cannot exceed the state ceilings, and must be sent to HCD within 60 days of adoption.
Quick facts
- Who adopts it
- The city council or county board of supervisors
- Standards allowed
- Objective only: parking, height, setback, landscape, architectural review, maximum size 1
- Review process
- Ministerial only; no discretionary process 3
- State oversight
- Copy to HCD within 60 days of adoption 7
- If it does not comply
- Null and void; state standards apply 3
Key takeaways
- An ADU ordinance is the part of a city or county code that sets local ADU rules.
- In California the ordinance is optional. Without a valid one, the state rules apply.
- A California ordinance may use objective standards only. It cannot be stricter than state law.
- The city must send a copy to HCD within 60 days of adopting it.
- A rule that breaks state law is null and void, even if it is still printed in the code.
- Outside California, the ordinance may be the only rule. Check your state first.
Why it matters to you
The ordinance is where your design meets real limits. It decides how tall the unit can be, how far from the fence it sits and what the roof must look like. Your designer will draw to it.
It also shapes cost and time. A design rule, such as matching the house siding, can add work. A clear ordinance makes plan check faster, because the planner only checks fixed rules.
Last, ordinances go out of date. If you read an old rule and design around it, you may give up space you were allowed to use. Knowing how to check the ordinance against state law protects you from that.
The ordinance in plain English
Every city and county in the US has a zoning code. An ADU ordinance is the part of it that deals with backyard cottages, garage conversions and units inside a house.
It is where you find the local numbers: the height limit for a detached unit, the setback from a side fence, whether the roof pitch must match the main house.
In most states the ordinance is the whole story. In California it is the second layer. State law, now in Chapter 13 of the Government Code, sets the outer limits, and the local ordinance fills in detail inside them. The California ADU law page explains that statute and its renumbering.
The stack below shows the order in California. Each layer must fit inside the one above it.
- State ADU law (Gov. Code Chapter 13)Sets the ceilings: what a city may and may not require 1
- Local ADU ordinanceFills in objective local numbers inside those ceilings
- Zoning district and overlaysWhich ordinance rules apply to your lot
- Your site planThe unit drawn to the strictest valid number from each layer
California only. In a state without an ADU statute, the local ordinance is the top layer. Source: [1]
What a California ordinance may and may not do
| A local ordinance may | A local ordinance may not | Section |
|---|---|---|
| Designate areas where ADUs are allowed, based on water and sewer adequacy, traffic and public safety | Set a minimum lot size for an ADU | 66314(a), (b)(1) |
| Impose objective standards: parking, height, setback, landscape, architectural review, maximum size | Add standards beyond 66314, including an owner-occupant requirement for an ADU | 66314(b)(1), 66315 |
| Reduce or eliminate ADU parking | Require more than one space per unit or per bedroom, or any parking in the 66322 cases | 66314(b)(2), (d)(10); 66322 |
| Require ADU rentals to be 30 days or longer | Use a discretionary process, hearing or variance | 66315, 66316, 66317 |
| Set side and rear setbacks for a new ADU | Require more than 4 feet, or any setback for a converted existing structure | 66314(d)(7) |
How HCD reviews an ordinance
The Department of Housing and Community Development (HCD) has a review role that is set out in Section 66326 7.
- The city or county adopts the ordinance and sends a copy to HCD within 60 days.
- HCD may send written findings on whether it complies with the state article.
- If HCD finds it does not comply, the agency gets a reasonable time, no longer than 30 days, to respond.
- The agency either amends the ordinance or re-adopts it with findings explaining why it believes the ordinance complies.
- If it does neither, HCD notifies the agency and may notify the Attorney General that it is in violation of state law.
The California ADU ordinance tracker follows how cities have responded.
When the ordinance is out of date
Ordinances lag the statute. The state amends the ADU chapter most years, and a city's text may still carry a rule the Legislature has since removed.
Section 66316 handles that: an ordinance that fails to meet the article is "null and void", and the agency must apply the state standards instead until it adopts a compliant one 3.
In practice that means the printed ordinance is not always the rule a planner should apply. If a local requirement looks stricter than the state ceiling, compare it with the current section, then ask the planning department which rule it is applying and why. The statute change log dates each state change.
- If The rule is within the current state ceiling
- Then Design to it; it is enforceable
- If The rule is stricter than the current state section
- Then Ask the planner in writing which standard applies; under § 66316 the state standard governs 3
- If The planner still applies the stricter rule
- Then Ask for the code section in writing; HCD reviews ordinances for compliance under § 66326 7
- If You are outside California
- Then The local rule may be the only rule; check your state law
Jurisdiction and date
The null-and-void rule is California’s (Gov. Code § 66316), read 7 October 2026. Other states have no matching rule unless their own statute says so.
Example: reading one ordinance clause against state law
A hypothetical ordinance clause, used only to show the check. The state figures come from the current sections.
| Hypothetical local clause | California ceiling | Result |
|---|---|---|
| "Detached ADUs shall be set back 10 feet from side and rear lot lines." | No more than 4 feet for a new ADU (66314(d)(7)) | Cannot be enforced as written |
| "One covered space required per ADU." | Max one space per unit or bedroom, may be tandem on a driveway; none within half a mile walking distance of public transit (66314(d)(10), 66322(a)(1)) | Partly valid; covered requirement and transit lots need checking |
| "Owner must live on site." | Owner-occupant requirement barred for ADUs (66315) | Cannot be enforced against an ADU |
| "Roof pitch shall match the primary dwelling." | Objective architectural standards allowed (66314(b)(1)) | Generally allowed |
This is an illustration of method, not a ruling on any real ordinance. The planning department applies the rules; disputes go to HCD or the courts.
How to find and read your ordinance
- Find your zoning district on the city or county zoning map.
- Open the municipal code online and find the zoning title. ADU rules often have their own chapter.
- Note the adoption or amendment date at the bottom of the section.
- List each number that limits you: height, setbacks, size, parking, design rules.
- Compare each number with the current state section on leginfo.legislature.ca.gov.
- Mark anything that looks stricter than state law, and ask the planner about it in writing.
The kinds of rules an ordinance holds
| Kind of rule | Plain meaning | Example of an objective rule |
|---|---|---|
| Location | Which zones and lots may have an ADU | ADUs allowed on lots with a single-family home |
| Size and height | How big and tall the unit can be | A stated maximum floor area and height in feet |
| Setbacks | Distance from lot lines | A stated number of feet from the side and rear lines |
| Design | How the unit must look | Roof pitch or exterior finish matching the main house |
| Parking | Off-street spaces required, if any | One space, tandem on a driveway allowed |
| Process | How an application is filed and reviewed | A checklist of plans and forms |
Where you will see it
- The municipal code. The legal text, usually in the zoning title.
- The city ADU web page or handout. A summary. It may lag the code.
- Plan check comments. A planner cites the ordinance section when asking for changes.
- Your site plan. Setback lines and the height limit drawn on the plans come from it.
- HCD letters. When HCD reviews an ordinance, its findings name the rules it questions.
What a local ordinance does well and where it falls short
Benefits
- Gives clear local numbers a designer can draw to
- Can be more generous than state law
- Can lower or remove parking
Limits
- Often lags behind yearly changes in state law
- Summaries on city web pages may not match the code
- Design rules can add cost even when lawful
Ordinance compared with related rules
| Rule | Who sets it | What it controls |
|---|---|---|
| State ADU law | The California Legislature | The ceilings every city must respect |
| Local ADU ordinance | The city council or county board | Local detail inside the ceilings |
| Zoning code | The city council or county board | Land use for all buildings, not just ADUs |
| Building code | The state, adopted locally | How the unit is built: structure, fire, wiring |
What to ask the planning department
- Which version of the ADU ordinance applies to my application?
- Has the city updated it since the latest state changes?
- Has HCD sent findings on this ordinance?
- Which section supports this requirement, and is it objective?
- Will you apply the state standard if a local rule conflicts with it?
- Do any overlay zones, such as a historic district, apply to my lot?
Checklist before you design
- Save a dated copy of the ordinance text you are relying on.
- Write down every number that limits the unit.
- Check each number against the state section.
- Confirm design rules with photos of the main house.
- Ask about anything unclear in writing, and keep the reply.
- Recheck the ordinance if your project pauses for months.
Ordinances outside California
Where a state has no ADU statute, the local ordinance is the only rule and can set lot-size minimums, owner-occupancy or parking freely. Where a state has passed one, the ceilings differ from California's. Check your state before reading a city code.
Related research and tools
- ADU regulations hub
- City and county ADU guidesWhere local rules are summarized
- California ADU enforcement record
- Feasibility checkerTest a lot against the state ceilings
Questions about local adu ordinance
Does every California city need an ADU ordinance?
No. Section 66314 says a local agency "may" adopt one. A city without a compliant ordinance must apply the state standards in the article, under Section 66316.
Can a city ban ADUs?
Not in residential zones in California. An ordinance may designate areas based on water and sewer adequacy, traffic and safety, and Section 66323 requires ministerial approval of certain ADUs in residential or mixed-use zones regardless of local rules.
What happens if my city's ordinance conflicts with state law?
Under Section 66316 the non-compliant ordinance is null and void and the state standards apply. HCD can issue findings and refer a city to the Attorney General under Section 66326.
Where do I find my city's ADU ordinance?
In the municipal or county code, usually the zoning title, and often on the planning department's ADU page. Check its adoption date against the latest state changes.
Is an ADU ordinance the same as a building code?
No. The ordinance is zoning: where and how big. The building code governs how it is built, and ADUs follow the code for detached dwellings under Section 66314(d)(8).
Can a California city require a minimum lot size for an ADU?
No. Section 66314 bars a local ADU ordinance from setting a minimum lot size for an ADU. The city may still apply its other objective standards, as long as they stay within the state ceilings.
Can my city require a hearing for my ADU?
No, not in California. ADU applications get ministerial review under Section 66317, with no discretionary review or hearing. A planner checks the plans against fixed, objective rules.
How do I know if my city ordinance is out of date?
Check the adoption date at the bottom of the code section. Then compare each number with the current state section. If a local rule looks stricter, ask the planner which rule applies.
Who checks that a city ordinance follows state law?
HCD. Under Section 66326 the city must send its ordinance to HCD within 60 days of adoption. HCD can issue findings and may notify the Attorney General if the city does not fix it.
Can a city require design rules for an ADU?
Yes, if they are objective. Section 66314 allows standards such as architectural review and landscape rules. A rule that needs a judgment call does not fit ministerial review.
Sources
- California Legislative Information, Gov. Code § 66314, retrieved .
- California Legislative Information, Gov. Code § 66315, retrieved .
- California Legislative Information, Gov. Code § 66316, retrieved .
- California Legislative Information, Gov. Code § 66317, retrieved .
- California Legislative Information, Gov. Code § 66322, retrieved .
- California Legislative Information, Gov. Code § 66323, retrieved .
- California Legislative Information, Gov. Code § 66326, retrieved .
- California Legislative Information, Gov. Code § 66333, retrieved .
Expert review
Written by the HyreADU Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Each permission and prohibition was checked against the current section text on leginfo.legislature.ca.gov on 7 October 2026. The worked example is hypothetical. Held for licensed review (G-REV).
Suggest a correction. We fix errors and say what changed.