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California law gives homeowners specific, measurable rights to build accessory dwelling units — and those rights expanded again on January 1, 2026. After nearly a decade of designing and permitting ADUs across Los Angeles County, I can tell you that most homeowners (and frankly, some planning departments) still get these rules wrong. This guide covers exactly what California Government Code §§66310–66342 allows, what changed with SB 543 and AB 1154, and what those numbers mean for your specific property.
Every regulatory fact in this post is sourced from the statute itself. No secondhand interpretations, no blog-post telephone game. Where I reference a specific rule, I cite the Government Code section so you can verify it yourself.
California ADU Rules: The Foundation
California’s ADU statute lives in Government Code Chapter 13, sections 66310 through 66342. The statute was renumbered and reorganized in 2024 (previously it was all under §65852.2), so if you see older references online, they may still point to the old section numbers. The substance is the same.
The key principle: State law sets a floor of rights. Local cities can adopt their own ADU ordinances, but those ordinances cannot be more restrictive than what state law guarantees. If a city tries to impose rules stricter than the statute allows, that ordinance is void and the state standards apply instead (Gov. Code §66316). The California Department of Housing and Community Development (HCD) actively reviews local ordinances and has issued enforcement letters to dozens of jurisdictions — including the City of Los Angeles (most recently in November 2025) and Los Angeles County (December 2025).
This matters because it means you have a guaranteed baseline, regardless of what your city’s planning counter tells you. If a planner says you need a 7,500-square-foot lot to build an ADU, that is wrong. State law explicitly prohibits minimum lot size requirements (Gov. Code §66314(b)(1) and §66321(b)(3)). That is not an interpretation — it is the text of the law.
ADU Size Limits in California (2026)
Size is now measured by “interior livable space.” This is a 2026 change introduced by SB 543 (Chapter 520, effective January 1, 2026). Previously, the statute referenced “living area.” The new term — “livable space” — is defined as space intended for human habitation, including living, sleeping, eating, cooking, and sanitation areas (Gov. Code §66313(e)). It includes bedrooms, bathrooms, kitchens, hallways, and closets. It does not include garages, covered patios, or exterior porches.
| ADU Configuration | Maximum Interior Livable Space | Statute |
|---|---|---|
| Studio or 1-bedroom (attached or detached) | 850 square feet | §66321(b)(2)(A) |
| 2+ bedroom (attached or detached) | 1,000 square feet | §66321(b)(2)(B) |
| Detached ADU — total floor area cap | 1,200 square feet | §66314(d)(5) |
| Attached ADU | 50% of existing primary dwelling | §66314(d)(4) |
| Junior ADU (JADU) | 500 square feet | §66313(d) |
These are floors, not ceilings. Cities must allow ADUs at least this large. They cannot cap your ADU below 850 square feet for a studio/one-bedroom or below 1,000 square feet for a two-bedroom-or-larger unit. A city can choose to be more generous, but it cannot restrict you below these thresholds (Gov. Code §66321(b)(2)).
Additionally, cities cannot impose any combination of lot coverage, floor area ratio, open space, front setback, or minimum lot size requirements that would prevent you from building at least an 800-square-foot ADU with 4-foot side and rear setbacks (Gov. Code §66321(b)(3)). This provision exists specifically to prevent cities from using indirect rules to block ADU construction.
Our Signature Home lineup ranges from 400 square feet (The Wilshire studio) to 1,200 square feet (The Culver, a 3-bedroom/2.5-bath two-story), all designed to maximize what state law guarantees you can build.
ADU Height Limits in California (2026)
Height depends on three factors: whether the ADU is detached or attached to the primary dwelling, your lot’s proximity to public transit, and whether the lot has a single-family or multifamily dwelling. The statute lays out four specific tiers.
| ADU Type | Condition | Maximum Height | Statute |
|---|---|---|---|
| Detached, single-family lot | Base (any location) | 16 feet | §66321(b)(4)(A) |
| Detached, single-family lot | Within ½ mile of transit or high-quality transit corridor | 18 feet (+2 ft for roof pitch) | §66321(b)(4)(B) |
| Detached, multifamily lot | Any location | 18 feet | §66321(b)(4)(C) |
| Attached to primary dwelling | Any location | 25 feet or local height limit (whichever is lower) | §66321(b)(4)(D) |
The 25-foot tier applies only to attached ADUs. This is one of the most common misunderstandings I see. Section 66321(b)(4)(D) explicitly states it applies to an ADU “that is attached to a primary dwelling.” It does not apply to detached ADUs. If someone tells you that you can build a 25-foot detached ADU under state law, they are reading the wrong subsection.
These are floors, not ceilings. The state height numbers above are the minimums that cities must allow. Your city’s local ordinance may permit taller ADUs based on the underlying zoning for your property. In the City of Los Angeles, for example, ADU height limits are often set by the zone’s base height limit, which ranges from 28 to 45 feet in most residential zones — well above the state minimums. This is a significant advantage for LA homeowners, because it means two-story detached ADUs are generally permitted with comfortable ceiling heights and proper roof pitch, even on lots that are not near transit. Check your specific zone’s height limit with LADBS or your ADU designer to confirm what applies to your property.
The transit bonus still matters. Even in cities that already allow generous heights, the state transit bonus (§66321(b)(4)(B)) provides a backstop: if your lot is within one-half mile of a major public transit stop or high-quality transit corridor, the state guarantees at least 18 feet plus 2 feet for roof pitch — regardless of what the local ordinance says. In Los Angeles, a huge number of residential properties fall within one-half mile of a Metro bus stop or rail station. This state floor is especially important in smaller cities and unincorporated areas where local zoning may be more restrictive.
Two-story ADUs are widely feasible in LA. Between the City of LA’s generous zone-based height limits and the state’s transit proximity bonus, most residential lots in the LA metro area can accommodate a two-story detached ADU. This is exactly why we developed our two-story Signature Home collection (The Fairfax, The Venice, and The Culver) — they deliver 840 to 1,200 square feet of living space on compact footprints that fit lots where a single-story of the same size would not.
A note on stories: The statute says that the 25-foot attached ADU provision “shall not require a local agency to allow an accessory dwelling unit to exceed two stories” (Gov. Code §66321(b)(4)(D)). This means the state does not force cities to allow three-story ADUs — but it does not prevent cities from allowing them either. Whether your ADU can be one story or two depends on your local height limit and building code constraints, not a blanket state restriction.
ADU Setback Rules in California (2026)
New construction detached ADUs require 4-foot side and rear setbacks. That is the state standard (Gov. Code §66321(b)(3)). Four feet from the side property line, four feet from the rear property line. There is no state-mandated front setback for ADUs — your local ordinance governs the front.
This 4-foot rule is one of the most powerful provisions in the statute. In most LA residential zones (R1, R2, RE), primary dwellings require 5-foot side setbacks. A detached ADU gets the tighter 4-foot setback regardless of your local zoning. That extra foot on each side adds 2 feet of buildable width across your lot — which can be the difference between fitting a two-bedroom and being limited to a one-bedroom.
Real-World Example: Setbacks on a Typical LA Lot
A standard 50-foot-wide lot in an R1 zone: local zoning requires 5-foot side setbacks for the main house, but a detached ADU only needs 4 feet on each side. That gives you 42 feet of buildable width for the ADU. On a tighter 35-foot-wide lot (common in many Westside and Valley neighborhoods), you still get 27 feet of buildable width — more than enough for a full two-bedroom layout. We have designed and permitted ADUs on lots as narrow as 30 feet.
Converted structures: no additional setback required. If you are converting an existing garage or accessory structure into an ADU, and the structure stays in the same location and same dimensions, no new setback is required (Gov. Code §66314(d)(7)). A garage that sits 2 feet from the property line can become an ADU at 2 feet from the property line.
No minimum lot size. I am repeating this because it is the single most common misconception I encounter. California law explicitly prohibits local agencies from imposing minimum lot size requirements for ADUs (Gov. Code §66314(b)(1) and §66321(b)(3)). If your lot is zoned for single-family or multifamily residential and has an existing or proposed dwelling, you can build an ADU. Period.
Parking Requirements for ADUs in California
In most of Los Angeles, parking is not required for ADUs. Gov. Code §66322 lists six scenarios where a city cannot impose any parking requirement:
- Transit proximity. The ADU is within one-half mile of public transit (a bus stop or train station with fixed-route, fare-based service).
- Historic district. The property is in an architecturally and historically significant historic district.
- Part of main house. The ADU is part of the primary residence or an accessory structure (interior conversion, garage conversion).
- On-street permits not offered. On-street parking permits are required in the area but not offered to the ADU occupant.
- Car share available. A car-share vehicle is within one block of the property.
- New dwelling application. The ADU permit is submitted alongside a new single-family or multifamily dwelling permit.
The transit proximity exemption alone covers a large percentage of LA properties. If none of the exemptions apply, the maximum parking requirement is one space per ADU (not per bedroom). That space can be provided as tandem parking on a driveway (Gov. Code §66314(d)(10)(A)).
Demolished garage parking does not need to be replaced. If you demolish a garage to build a detached ADU, the city cannot require you to replace the lost parking spaces (Gov. Code §66314(d)(11)). This is critical for garage demolition-and-rebuild projects.
ADU Permitting: Timelines and Process
ADU permits are ministerial. That means no public hearing, no discretionary design review, no conditional use permit, and no neighborhood notification (Gov. Code §66317(a)(1)). If your plans meet objective standards, the city must approve them. This is not optional — the statute uses the word “shall.”
The 60-Day Approval Clock
Once your application is deemed complete, the permitting agency has 60 days to approve or deny it (Gov. Code §66317(a)(3)). If they do not act within 60 days, the application is deemed approved by operation of law. This is a powerful provision that prevents cities from sitting on applications indefinitely.
New in 2026: The 15-Business-Day Completeness Check
SB 543 added a new requirement effective January 1, 2026: the permitting agency must determine whether your application is complete and notify you in writing within 15 business days of receiving it (Gov. Code §66317(a)(2)(A)). If they determine it is incomplete, they must provide a specific list of missing items and how to cure them (§66317(a)(2)(B)). If the agency fails to make this determination within 15 business days, the application is deemed complete (§66317(a)(2)(F)).
This is a significant protection for homeowners. Before SB 543, some jurisdictions would accept applications and then take months to review them before declaring them incomplete — effectively resetting the clock. The 15-business-day rule puts a hard deadline on that game.
Appeal Rights
If your ADU permit application is denied, you have the right to appeal to the governing body (city council, board of supervisors) or, at the city’s option, to the planning commission. The appeal must be decided within 60 business days (Gov. Code §66317(d)(2)). This appeal right was clarified by SB 543.
Fees: What You Will and Will Not Pay
No impact fees on ADUs under 750 square feet. If your ADU has 750 square feet or less of interior livable space, no impact fees can be charged (Gov. Code §66311.5(c)(1)). For ADUs over 750 square feet, impact fees must be proportional to the primary dwelling’s square footage — meaning they are a fraction of what a new single-family home would pay.
No new utility connection required for certain ADUs. For ADUs and JADUs built under the state-mandated provisions of §66323 (which includes most interior conversions and one detached new construction ADU per lot), no new or separate utility connection fee or capacity charge can be imposed (Gov. Code §66311.5(d)). For other ADUs, a connection may be required, but the fee must be proportional to the ADU’s burden on the system, based on square footage or drainage fixture units (Gov. Code §66311.5(e)).
School fees are exempted for small ADUs. An ADU or JADU under 500 square feet of interior livable space is considered construction that does not increase assessable space by 500 square feet for purposes of Education Code §17620 school fees (Gov. Code §66311.5(c)(3)).
In practice, total permit and plan check fees for a detached new construction ADU in the City of Los Angeles range from roughly $1,500 for a garage conversion to $7,500 for a large 1,200-square-foot detached ADU. The exact amount depends on the project valuation LADBS assigns and whether school district fees and energy surcharges apply. We break down the actual LADBS fee calculations with real permit examples in our ADU permit cost guide. We handle all permit processing as part of our Signature Home projects — the only fees you pay directly are city permit fees at cost.
What Changed in 2026: SB 543 and AB 1154
Two bills took effect January 1, 2026 that meaningfully changed ADU rules in California. Here is what each does.
SB 543 (McNerney) — Chapter 520
SB 543 amended sections 66311, 66313, 66317, 66320, 66321, 66323, and 66335 of the Government Code. The key changes:
- Size measurement basis changed. ADU size limits are now based on “interior livable space” rather than “living area.” The practical difference is subtle but important: “livable space” is more precisely defined to include all habitable areas (living, sleeping, eating, cooking, sanitation) while “living area” had a broader definition that included basements and attics. This change provides clearer guidance on what counts toward the 850/1,000-square-foot thresholds.
- 15-business-day completeness check. Agencies must determine application completeness within 15 business days. Failure to do so means the application is deemed complete.
- JADU ordinance review. HCD’s authority to review local ADU ordinances now extends to JADU ordinances as well.
- Appeal process codified. Applicants have a clear right to appeal denied applications to the governing body, with a 60-business-day decision deadline.
AB 1154 (Carrillo) — Chapter 507
AB 1154 amended section 66333 of the Government Code (the JADU section). The changes are narrow but significant for JADU projects:
- Owner-occupancy relaxed for JADUs. Previously, JADU ordinances required the property owner to live on-site. AB 1154 limits this requirement to JADUs that share sanitation facilities (bathroom) with the existing structure (Gov. Code §66333(b)). If the JADU has its own bathroom, no owner-occupancy is required.
- Government and nonprofit exemption. Owner-occupancy is also waived if the owner is a governmental agency, land trust, or housing organization.
- JADU requirements codified. AB 1154 explicitly lists JADU requirements: maximum one per single-family lot, must be within the walls of the existing or proposed single-family residence (attached garages count), separate entrance required, efficiency kitchen required (cooking facility, food prep counter, storage), and rentals must be for terms longer than 30 days.
For standard ADUs (not JADUs), there is no owner-occupancy requirement. This has been the case since 2020, but it bears repeating. You can build an ADU on your property and rent out both the main house and the ADU. You do not have to live on-site. See our ADU investment guide for the rental income math.
State-Mandated ADUs: What Cities Must Approve (§66323)
Section 66323 is the most powerful provision in the statute. It lists specific ADU configurations that cities must approve regardless of their local ordinance. No exceptions, no discretionary review. These are sometimes called “66323 units” or “by-right” ADUs.
The critical language is in the opening sentence of §66323(a): cities must approve “any of the following units, or any combination of the following units.” That word “combination” is key. On a single-family lot, you are not choosing between these options — you can build all of them together.
Single-Family Lots: Up to Three Units
A single-family homeowner can add all three of the following on one lot:
- One interior conversion ADU and one JADU — if the ADU or JADU is within the existing space of the home or an accessory structure, with no more than 150 square feet of expansion beyond the existing footprint (§66323(a)(1)).
- One detached new construction ADU — up to 800 square feet of livable space, with 4-foot side and rear setbacks, subject to the applicable height limits (§66323(a)(2)).
That means a single-family property could potentially have the main house, a JADU (within the house or attached garage), a conversion ADU (in a detached garage, for example), and a brand-new detached ADU in the backyard — all by right under state law. For most of our clients, the detached new construction ADU under §66323(a)(2) is the starting point, and a JADU or conversion ADU is an additional opportunity worth exploring.
Multifamily Lots: Significant ADU Potential
On a lot with an existing multifamily dwelling, a city must approve:
- Interior conversion ADUs within non-livable portions of existing multifamily structures (storage rooms, boiler rooms, garages, etc.). At least one unit must be allowed, and cities must permit up to 25% of the existing dwelling count (§66323(a)(3)).
- Up to eight detached ADUs on a lot with an existing multifamily dwelling — though the total number of detached ADUs cannot exceed the number of existing units on the lot (§66323(a)(4)(A)(ii)). On a lot with a proposed (not yet built) multifamily dwelling, the limit is two detached ADUs (§66323(a)(4)(A)(iii)).
The §66323 provisions are especially important because ADUs under 750 square feet that qualify under this section are exempt from impact fees and may not require new utility connections.
Fire Sprinklers, Building Code, and Other Standards
Fire sprinklers are not required unless the primary dwelling requires them. The construction of an ADU cannot trigger a sprinkler requirement in the existing main house either (Gov. Code §66314(d)(12)). This saves homeowners thousands of dollars. If you are building a new detached ADU on a lot with an existing single-family home that was built without sprinklers, your ADU will not need them either.
Local building code applies to detached ADUs as it would to any detached dwelling, with one important caveat: the construction of a detached ADU does not constitute a Group R occupancy change under the California Building Code (Title 24) unless the building official makes a written finding of a specific adverse impact on public health and safety (Gov. Code §66314(d)(8)).
No passageway is required. A “passageway” is a clear path from the street to the ADU entrance. Cities cannot require one (Gov. Code §66314(d)(6)). You can access your ADU through a side gate or along an existing pathway.
What This Means for Your Property
The numbers above are state law. They apply to every single-family and multifamily residential lot in California. But the practical question is: what can you actually build on your specific lot, given its dimensions, topography, existing structures, and utility connections?
That is where experience matters. We have designed and permitted ADUs on narrow lots, hillside lots, lots with easements, lots with existing nonconforming structures, and lots where previous companies told the homeowner an ADU was impossible. After nine years and projects across nearly every LA neighborhood, we have seen virtually every site condition this city can throw at you.
The state gives you the right to build. Knowing how to exercise that right efficiently — which model fits your lot, what your city will actually require, how to avoid the delays that add months to a project — is the difference between a smooth build and a painful one.
If you want to know exactly what you can build on your lot, our feasibility assessment takes 15 minutes and gives you a clear answer. No cost, no obligation. We will look at your specific property, tell you which Signature Home models fit, and give you a realistic timeline and cost estimate.
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