California ADU Rules: What Your City Must Allow

The numbers no city in California can go below

Size

A city may set its own maximum size for accessory dwelling units, but it cannot set that maximum below 850 square feet of interior livable space, or below 1,000 square feet for a unit with more than one bedroom (Government Code § 66321(b)(2)). Separately, no standard of any kind — floor area ratio, lot coverage, open space, front setback, minimum lot size, or a percentage of your existing house — may be applied in a way that prevents an ADU of at least 800 square feet with four-foot side and rear setbacks (§ 66321(b)(3)).

Those are floors, not ceilings. State law separately caps a detached ADU at 1,200 square feet of total floor area (§ 66314(d)(5)), and limits an attached ADU to 50 percent of the existing primary dwelling (§ 66314(d)(4)) — though that percentage cannot be used to push you below the 800-square-foot protection above. A junior ADU is a different animal: no more than 500 square feet, contained entirely within the walls of the single-family residence (§ 66313(d)).

Height

Government Code § 66321(b)(4) sets four height floors, and the one that applies to you depends on what is already on the lot and how close you are to transit:

• 16 feet for a detached ADU on a lot with an existing or proposed single-family or multifamily dwelling.
• 18 feet if the lot is within half a mile walking distance of a major transit stop or a high-quality transit corridor — plus a further 2 feet where that height is needed to accommodate a roof pitch aligned with the roof pitch of the main house.
• 18 feet for a detached ADU on a lot with an existing or proposed multifamily, multistory dwelling.
• 25 feet, or your city’s height limit for the main house, whichever is lower, for an ADU attached to the primary dwelling. No city is required to allow more than two storeys.

On a lot near a Metro stop that half-mile line is worth checking carefully, because it is measured as walking distance rather than as the crow flies. The difference between 16 and 18 feet is often the difference between a flat roof and a pitched one that matches your house.

Setbacks

For new construction, a city cannot require more than four feet from the side and rear lot lines (§ 66314(d)(7)). If you are converting an existing living area or accessory structure, or rebuilding in the same location and to the same dimensions, no setback may be required at all. That single provision is what makes a garage sitting on the property line convertible when a new building in the same spot would not be.

Parking is where homeowners are most often over-charged

Where a parking requirement applies at all, it is capped at one space per unit or per bedroom, whichever is less, and that space may be tandem, on your driveway, or inside a setback area (§ 66314(d)(10)). But in a long list of situations no parking standard may be imposed whatsoever (§ 66322(a)):

• The unit is within half a mile walking distance of public transit.
• It sits in an architecturally and historically significant historic district.
• It is part of the proposed or existing primary residence, or of an accessory structure — which covers every garage conversion and every junior ADU.
• On-street parking permits are required in your area but are not offered to the ADU occupant.
• There is a car share vehicle within one block.
• The ADU application is submitted alongside an application for a new single-family or multifamily dwelling on the same lot.

And if you demolish or convert a garage, carport, covered structure or uncovered space to build the ADU, your city cannot require you to replace that parking anywhere else on the lot (§ 66314(d)(11)). This is the provision most often quietly ignored, and it is worth knowing before someone designs you a new pad you do not owe.

Impact fees, and the 750-square-foot line

No impact fee may be charged on an ADU of 750 square feet or less of interior livable space, or on a junior ADU of 500 square feet or less. Above 750 square feet, impact fees may be charged — but only proportionally to the square footage of the primary dwelling, not at the full rate that would apply to a new house.

This rule used to sit at Government Code § 66324. As of 1 January 2026 it was renumbered to § 66311.5(c), so if you are reading an ADU guide that still cites § 66324, it has not been updated this year. One important limit: the exemption covers impact fees, not connection fees or capacity charges for water, sewer and power, which are a separate category and can still be charged.

The junior ADU rule that decides whether you have to live there

Nearly every guide states flatly that a junior ADU requires the owner to live on the property. That is only half true, and the half that gets left out is the half you can design around.

Under § 66333(b), owner-occupancy may be required only if the junior ADU shares sanitation facilities with the existing house. If the JADU has its own bathroom, owner-occupancy cannot be required of you. It also cannot be required where the owner is a government agency, land trust or housing organisation. A junior ADU does always require a recorded deed restriction running with the land, prohibiting its sale separately from the house (§ 66333(c)).

The clock: 15 business days, then 60 days

The permitting agency must determine whether your application is complete and tell you so in writing within 15 business days of receiving it. If it is incomplete, they must give you a list of the missing items and a description of how to remedy each one (§ 66317(a)(2)).

Once they hold a completed application, they have 60 days to approve or deny it. If they do neither, the application is deemed approved (§ 66317(a)(3)). A denial must arrive with full written comments listing exactly what is deficient and how to fix it — not a one-line rejection — and since 1 January 2026 you also have a right of written appeal, with a final determination due within 60 business days (§ 66317(b), § 66317(d)).

The word carrying all the weight there is completed. The clock does not start when you hand something in; it starts when the submittal is complete. That is precisely why a well-prepared first submittal is worth more than any amount of chasing afterwards.

One rule that is state law, not a local favour

An ADU cannot be required to have fire sprinklers if they are not required for the primary residence, and building an ADU cannot trigger a requirement to retrofit sprinklers into your existing house (§ 66314(d)(12)). This applies everywhere in California. If it is presented to you as a local concession, it is not one.

Sources

This tool applies California ADU statute, which the Legislature amends most years; city ordinances are updated separately and can lag it. The result is a guide to what state law protects, not a planning determination. Confirm with your city before you rely on it.

• California HCD, Accessory Dwelling Unit fact sheet (April 2026) — ADU law at Government Code sections 66310–66342: a city may not require rear and side setbacks greater than four feet for a new ADU, may not impose impact fees on an ADU under 750 sq ft or on a JADU, and must act on an application within 60 days (Gov. Code section 66317). It also records the 15-business-day completeness determination added by SB 543.
• California HCD, Accessory Dwelling Unit Handbook (March 2026) — Government Code section 66321(b)(3), the rule that local standards may not prevent at least an 800 sq ft ADU with four-foot setbacks at up to 16 feet.

Last reviewed 17 September 2026.

What this tool cannot tell you

Everything above is the statewide floor. None of it tells you whether your lot works, which is the question you actually want answered. What decides that is physical and local:

• Where your sewer lateral runs, and whether it has capacity for another unit.
• Whether your electrical panel can carry a second dwelling or needs upgrading first.
• Slope. Hillside lots in Studio City, Sherman Oaks and the Encino hills routinely need shoring, retaining or a stepped foundation that a flat lot in Van Nuys does not.
• Access for equipment and materials — alley access changes a build schedule more than most people expect.
• Easements, existing structures, and how the four-foot setback interacts with what is already in the yard.
• Which authority you are actually dealing with. LADBS, Burbank, Glendale and Pasadena each run their own process on top of these state rules.

We assess all of it in person, before you have spent anything, and tell you in writing what your lot will and will not take. If a pre-approved design fits your yard, our guide to Los Angeles pre-approved ADU standard plans explains that route. If you are weighing an ADU against simply making the house bigger, a room addition is a different calculation, and garage conversion is usually the cheapest way to a permitted unit. Our main ADU construction page covers how we work.

Rules summarised on this page reflect California accessory dwelling unit law as it stood in August 2026, following the amendments made by SB 543 (Stats. 2025, Ch. 520) effective 1 January 2026, and are drawn from the California Government Code (§§ 66311.5, 66313, 66314, 66317, 66321, 66322, 66323, 66333). Cities may adopt less restrictive rules than these, and requirements change. Confirm current requirements for your property with your permitting agency before making decisions. This page is information, not legal advice. Page last reviewed August 2026.