An accessory dwelling unit, or ADU, is a second home on the same lot as your house. California has a state law that sets the floor for what every city and county must allow. Los Angeles and LA County add their own local rules on top, but they cannot go below the state floor.
LA ADU Guide is an information site. We are not a contractor, architect, lender or law firm. Rules change, so confirm everything with your building department before you spend money.
Where the law lives now
The state ADU law used to sit in Government Code sections 65852.2 and 65852.22. SB 477 moved it, effective March 25, 2024, into Title 7, Division 1, Chapter 13, "sections 66310-66342." Many older articles, and some city ordinances, still cite the old numbers. HCD told the City of Los Angeles in November 2024 that its ordinance "contains several references to code sections that were deleted."
So if you read a guide that cites 65852.2, the content is probably still useful. Just look for the new section number before you rely on it.
What counts as an ADU
Section 66313 defines an ADU as "an attached or a detached residential dwelling unit that provides complete independent living facilities." It needs permanent provisions for living, sleeping, eating, cooking and sanitation. It also includes efficiency units and manufactured homes.
A junior ADU (JADU) is a smaller cousin. Section 66313(d) says it is "no more than 500 square feet in size and contained entirely within a single-family residence." See ADU vs. JADU vs. garage conversion for how the types compare.
How many units you can build
Section 66323(a) lists several kinds of ADUs a city "shall ministerially approve." On a lot with a single-family home, the main options are:
- One ADU and one JADU created from space inside the home or an existing accessory structure, such as a garage.
- One new detached ADU with side and rear setbacks of no more than four feet.
HCD's letter to Los Angeles says these can be combined, "in any order without prejudice, totaling three units." On a lot with an existing multifamily building, state law also allows converted ADUs inside non-livable space and up to eight detached ADUs, not to exceed the number of existing units (SB 1211, effective January 1, 2025).
Size limits
CAL FIRE's March 2025 bulletin summarizes the state size rules:
- Detached ADU: a local agency with its own ordinance may set a maximum, but not below 850 square feet (studio or 1 bedroom) or 1,000 square feet (2+ bedrooms). Where a city has no ADU ordinance, the limit is 1,200 square feet.
- Attached ADU: the same 850/1,000 square foot floor applies. Up to 50 percent of the main home applies only where a city has no ADU ordinance.
- A local agency may set maximums of "850 square feet for one bedroom or 1,000 square feet for more than one bedroom" for some ADUs.
- Under section 66321(b)(3), a city must allow at least 800 square feet, regardless of the size of the main home.
- Conversions of existing space under section 66323(a)(1) have no size limit.
Setbacks and height
For a new detached ADU, the state cap on side and rear setbacks is four feet. An existing structure converted in the same location and to the same dimensions needs no setback.
Since AB 2221 (2022), front setbacks cannot block an ADU of at least 800 square feet and 16 feet in height that meets the four-foot side and rear rule. HCD also notes that near major transit a city must allow 18 feet of height, plus up to two more feet to match the roof pitch of the main home (section 66321(b)(4)). Local rules can be more generous than this floor.
The 60-day clock
Section 66317 says the permitting agency "shall either approve or deny" a complete application within 60 days when there is an existing single-family or multifamily home on the lot. Approval is ministerial, which means staff check the project against objective standards instead of holding a discretionary hearing. Our permit process guide walks through what happens in Los Angeles.
Other rules worth knowing
- Owner occupancy. AB 976 (2023) removed owner-occupancy requirements for ADUs. JADUs still require the owner to live in the home or the JADU (section 66333).
- Existing code violations. Under section 66322(b), a city cannot deny an ADU because of building code violations "that do not present a threat to public health and safety and are not affected by the construction" of the ADU.
- Density. Section 66319 says a compliant ADU "shall not be considered to exceed the allowable density for the lot."
- Sales. ADUs generally cannot be sold separately from the main home, with narrow exceptions. AB 1033 (2023) lets cities with an ADU ordinance allow condo-style conveyance.
- Unpermitted ADUs. AB 2533 (effective January 1, 2025) extends amnesty to some unpermitted ADUs and JADUs built before 2020.
- Impact fees. Section 66311.5(c) says no impact fees for ADUs of 750 square feet or less (formerly section 66324). Larger ones are charged in proportion to the main home. See impact fees and utility connections.
Los Angeles is still catching up
HCD's 2024 review found 17 places where the City of Los Angeles ordinance (No. 186481, effective December 19, 2019) did not match state law. Examples include a ban on ADUs in lots that are in both a Very High Fire Hazard Severity Zone and a hillside area, and a two-story limit. State law controls where the city ordinance conflicts. In practice, ask the city which rule it is applying to your lot, and ask it to cite the section.
For lots in mapped fire zones, read ADUs in fire hazard zones. For splitting a lot, see SB 9 lot splits in Los Angeles.
State rules at a glance
| Topic | State rule | Where it comes from |
|---|---|---|
| Units on a single-family lot | One ADU and one JADU inside existing space, plus one new detached ADU | Gov. Code 66323(a) |
| Detached size | A local ordinance may set a maximum, but not below 850 sq ft (studio or 1 bedroom) or 1,000 sq ft (2+ bedrooms). 1,200 sq ft applies only where a city has no ADU ordinance | CAL FIRE bulletin 25-004 |
| Smallest ADU a city cannot block | 800 sq ft with 4 ft side and rear setbacks | Section 66321(b)(3) |
| Attached size | Up to 50 percent of the main home | CAL FIRE bulletin 25-004 |
| Conversions of existing space | No size limit | Section 66323(a)(1) |
| Side and rear setbacks | Four feet at most for a new detached ADU | Section 66323(a) |
| Review time | 60 days for a complete application | Section 66317 |
| Owner occupancy | Not required for ADUs, required for JADUs | AB 976; section 66333 |
| Impact fees | None for ADUs of 750 sq ft or less | Section 66311.5(c) |
Quick checklist
- Confirm which agency permits your address: City of Los Angeles, unincorporated LA County, or another city.
- Check your lot against the state minimums: 800 square feet, four-foot setbacks, 16 feet of height.
- Decide the type: conversion, detached, attached or JADU.
- Look up your fire zone and flood or hillside status.
- Ask the agency in writing which code sections it relies on.
- Verify any builder you hire at the state licensing board, covered in hiring an ADU builder.
This page is general information, not legal advice. Browse more in the ADU rules hub.
Sources
- HCD: Review of Los Angeles's ADU Ordinance under State ADU Law (Nov. 19, 2024)
- CAL FIRE Office of the State Fire Marshal, Information Bulletin 25-004: ADU Update (Mar. 3, 2025)
- California Department of Housing and Community Development: ADU Handbook
- California Government Code, Title 7, Division 1, Chapter 13 (sections 66310-66342)