Quick answer: In the City of Los Angeles, a detached ADU built under the City’s ADU ordinance can be up to 1,200 square feet and two stories within the zone’s height limit. State law separately guarantees a detached 800-square-foot ADU at 16 feet (18 feet near major transit, or 20 feet there with a roof pitch matching the house). An attached ADU is generally limited to 50% of the existing house, a garage conversion to the existing structure plus up to 150 square feet for entry and exit, and a junior ADU (JADU) to 500 square feet inside the house. California itself does not cap ADUs at 1,200 square feet: that is the state’s default, and cities may allow more. APLA Construction (CA Lic #1136359) designs every ADU around what your lot can legally hold.
Two sets of rules apply to every Los Angeles lot. The City’s ADU ordinance (LAMC § 12.22 A.33) allows the largest units but applies more zoning standards. The state’s “State ADU” categories (Government Code § 66323) are smaller but must be approved ministerially, with only the standards the statute allows. City Planning and LADBS explain how the two fit together in ZA Memorandum No. 143, Revision 1 (August 1, 2025). California’s ADU law now sits in Government Code §§ 66310–66342; older articles cite the former § 65852.2, which was renumbered.
| ADU type | Maximum size | Height | Side and rear setbacks | Parking |
|---|---|---|---|---|
| City ordinance ADU (detached or attached) | 1,200 sq ft detached; attached up to 50% of the house | Up to 2 stories, within the zone’s height limit | 4 ft for new construction | 1 space, unless an exception applies (for example, within ½ mile walking distance of a bus or rail stop) |
| State ADU — detached new construction | 800 sq ft | 16 ft; 18 ft within ½ mile of major transit (20 ft when the roof pitch matches the house) | 4 ft | None |
| State ADU — conversion of existing space | Existing space + up to 150 sq ft for entry/exit | Existing structure | None for the existing structure | None |
| Junior ADU (JADU) | 500 sq ft | Inside the house | — | None |
On a lot with a single-family home, the City must approve one detached, new-construction ADU of up to 800 square feet with 4-foot side and rear setbacks (Gov. Code § 66323(a)(2)). Its height can be limited to 16 feet, or 18 feet within ½ mile walking distance of a major transit stop or high-quality transit corridor, in which case 2 more feet are allowed when the roof pitch matches the main house (§ 66321(b)(4), as amended by SB 543 effective January 1, 2026). The City cannot add other objective design or development standards to it (§ 66323(b)), and no parking is required.
An attached ADU is generally limited to 50% of the existing house’s floor area. On a 1,800 sq ft home that is 900 sq ft. Smaller houses get a floor: in Los Angeles, an attached ADU under 850 sq ft (under 1,000 sq ft if it has more than one bedroom) may exceed the 50% limit (LAMC § 12.22 A.33(e)(3), ZA Memo 143). State law guarantees an attached ADU at least 25 feet of height or the zone’s limit for the house, whichever is lower, without requiring more than two stories (§ 66321(b)(4)(D)).
See our garage conversion ADU guide for layouts and utility rules.
Comparing the two? See our ADU vs. JADU guide.
Under Government Code § 66321(b)(3), no local size limit, size based on a percentage of the main house, lot coverage, floor area ratio, open space, front setback or minimum lot size rule may prevent an ADU of at least 800 square feet with 4-foot side and rear setbacks, provided it meets the city’s other development standards. In practice, even a Los Angeles lot that is already at its floor area or lot coverage limit can usually still fit an 800 sq ft ADU. Above 800 sq ft, the normal zoning limits apply. APLA checks this for every feasibility assessment.
No. State law works in two directions:
The City of Los Angeles uses 1,200 sq ft for a detached ordinance ADU. Other cities in the county, such as Pasadena, Glendale, Burbank and Santa Monica, set their own limits, so check the city your lot is in.
For the size limits, Los Angeles measures an ADU by the building code’s gross floor area: everything inside the exterior walls, without deducting closets, stairways, interior walls or columns (ZA Memo 143, Q.3, following HCD’s handbook). A design that “feels” like 750 sq ft of living space can measure larger than that on the permit drawings, which matters for both the limits on this page and the fee thresholds below.
At 750 sq ft or less, no impact fees can be charged on an ADU (Gov. Code § 66311.5(c)(1)); under 500 sq ft, it also avoids school fees. Our ADU floor plans guide shows how those lines shape common layouts, and our ADU cost guide covers the budget.
For two-story designs, see our two-story ADU guide.
1,200 sq ft for a detached ADU under the City’s ordinance, which can be two stories within the zone’s height limit. An attached ADU is generally capped at 50% of the existing house (with an exception for units under 850 sq ft, or under 1,000 sq ft with more than one bedroom), and a JADU at 500 sq ft. The state’s detached “State ADU” is 800 sq ft.
No. 1,200 sq ft is the state’s default for a detached ADU where a city has no compliant ordinance. Cities may allow larger ADUs, and none may set a maximum below 850 sq ft (1,000 sq ft with more than one bedroom).
Not for an ADU of up to 800 sq ft with 4-foot side and rear setbacks. Government Code § 66321(b)(3) prevents lot coverage, floor area ratio, open space, front setback and minimum lot size rules from blocking one. Above 800 sq ft, the normal limits apply.
4 feet from the side and rear lot lines for new construction. An existing structure converted to an ADU keeps its existing setbacks, even if they are less than 4 feet.
Only if the JADU shares a bathroom with the house. A JADU with its own bathroom has no owner-occupancy requirement under Government Code § 66333(b).
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Email: info@aplaconstruction.com
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ADU Construction Los Angeles | ADU Permit Process Los Angeles | ADU vs JADU Los Angeles | ADU Cost Los Angeles 2026
Sources, read October 2026: California Government Code § 66313, § 66314, § 66321, § 66323, § 66333 and § 66311.5; HCD Accessory Dwelling Unit Handbook; Los Angeles City Planning and LADBS ZA Memorandum No. 143, Revision 1 (Aug. 1, 2025); LADBS ADU page. Zoning varies by lot (hillside, fire zone, specific plans), so confirm your property’s limits before design. General information, not legal advice.