ADU Guide · Verified 2026
Building an ADU in California
California has the most permissive ADU law in the country. Since 2020 every city and county must approve a qualifying ADU ministerially — no public hearing, no discretionary design review, no neighbor objection. If your plans meet the objective standards the agency must approve them, and it has 60 days to act once your application is complete or the permit is deemed approved.
Quick Facts
Statewide floors set by California Government Code, Title 7, Div. 1, Chapter 13 (§§ 66314-66339). Your city may be more generous but cannot go below them.
The Three Types of ADU
What you can build by right
State law sets a floor no city can go below. A local agency cannot combine lot-coverage, floor-area-ratio, open-space, front-setback or minimum-lot-size rules in any way that would stop an ADU of at least 800 sq ft of interior livable space with four-foot side and rear setbacks (Gov. Code § 66321(b)(3)). Detached ADUs get at least 16 ft in height, 18 ft within a half-mile walking distance of a major transit stop or high-quality transit corridor, plus up to two feet to match the primary home roof pitch (§ 66321(b)(4)). A studio or one-bedroom cannot be capped below 850 sq ft, a two-bedroom-or-larger below 1,000 (§ 66321(b)(2)). There is no state minimum lot size.
How many you can have
On a single-family lot you may build one standard ADU plus one Junior ADU — up to two additional units alongside the main house. On multifamily properties the math differs: you can convert non-livable space into multiple ADUs and add detached units under separate provisions of the same chapter. The one-ADU-plus-one-JADU combination is the case almost every homeowner is asking about.
You do not have to live on the property
For a standard ADU there is no owner-occupancy requirement, and AB 976 made that permanent effective January 1, 2024. You can rent out both the main house and the ADU. Long-term rentals of 30+ days are allowed statewide; short-term (Airbnb-style) rental is left to each city. The only exception is a Junior ADU that shares a bathroom with the main house.
How approval works — ministerial, 60 days
ADU permits are ministerial (Gov. Code § 66317): no public hearing, no conditional use permit, no design review board, no neighborhood notification. If the plans meet the objective standards the agency must approve them. Once your application is complete the agency has 60 days to act, and a missed deadline means the permit is deemed approved. Effective January 1, 2026, SB 543 adds a 15-business-day window for the agency to tell you in writing whether your application is complete.
Parking is usually waived
A new ADU nominally needs one off-street space, but the exemptions cover most lots (Gov. Code § 66322): none is required within a half-mile walking distance of transit, in a historic district, as part of the primary residence or an existing accessory structure, where on-street permits are required but not offered to the ADU occupant, or within one block of a car-share. Converting a garage into an ADU does not trigger a requirement to replace the lost parking.
Junior ADUs are a separate category
A Junior ADU (JADU) is up to 500 sq ft and sits entirely within the walls of an existing single-family home. Same ministerial process, but owner-occupancy works differently: as of January 1, 2026 (AB 1154), it is required only when the JADU shares sanitation facilities with the main house. Give the JADU its own bathroom and the owner no longer has to live on site.
Fees and what still applies
ADUs under 750 sq ft are exempt from development impact fees; units under 500 sq ft are also exempt from school fees. You still pull a building permit and pass inspections — the ministerial rule removes the discretionary land-use review, not the safety review. Local objective building, health and safety standards still apply, as do utility connections. An HOA cannot prohibit ADUs outright but may impose reasonable objective design standards.
What people get wrong
Three misconceptions cost homeowners time. First, that you must live on the property — false for a standard ADU since 2020, permanent since 2024. Second, that an ADU and a Junior ADU are the same thing — they are separate categories with different size limits and rules, and you can have one of each. Third, that you can sell the ADU separately from the main house — generally you cannot, unless your city has opted into AB 1033. The ADU adds value and rental income but stays legally tied to the primary home.
What changed for 2026
Three bills took effect January 1, 2026. SB 543 shifted size limits to interior livable space, added the 15-business-day completeness check, and extended HCD review to JADU ordinances. AB 1154 relaxed JADU owner-occupancy to apply only when the JADU shares sanitation with the main house. AB 462 lets a homeowner in a declared-emergency county get a certificate of occupancy for a rebuilt ADU before the primary dwelling is reconstructed. These sit on a settled framework: ministerial approval (AB 68, 2019), permanent removal of owner-occupancy (AB 976, 2024), and optional separate condo sale where a city opts in (AB 1033).
From Idea to Move-In: The Timeline
Who Administers It
Check Your County
Select your county for local rules, fees, and your building department's contact details:
Building It Yourself? Here's What You'll Need
Planning an ADU? Tools homeowners use in the design and layout phase:
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Check Your Local Rules
Your city may allow more than the state floor
State law sets the minimum; many California cities are more generous. Confirm specifics with your local planning department.
Find your county building department →Not sure if your project needs a building permit, a zoning approval, or both? See our guide to building permits vs. zoning approval.
Official Sources
ADU law changes frequently and local ordinances add detail. This guide is general information, not legal advice — always confirm with your local building department. Reviewed by the StateDataIndex Editorial Team · Updated July 2026.