How Many ADUs Per Lot California Allows: 66323 Cap

What state law allows on a single-family lot

Government Code Section 66323(a)(1) requires a local agency to ministerially approve one accessory dwelling unit and one junior accessory dwelling unit per lot with a proposed or existing single-family dwelling if the ADU or JADU is within the proposed or existing space of the single-family dwelling or an existing accessory structure, has exterior access from the proposed or existing single-family dwelling, has side and rear setbacks sufficient for fire and safety, and, for the JADU, complies with the requirements of Article 3 commencing with Section 66333. The same subdivision allows an expansion of not more than 150 square feet beyond the same physical dimensions as the existing accessory structure, and limits that expansion to accommodating ingress and egress.

Government Code Section 66323(a)(2) requires a local agency to ministerially approve one detached, new construction, accessory dwelling unit that does not exceed four-foot side and rear yard setbacks for a lot with a proposed or existing single-family dwelling. The local agency may impose a total floor area limitation of not more than 800 square feet of livable space on that detached unit and a height limitation under subparagraph (A), (B), or (C) of paragraph (4) of subdivision (b) of Section 66321, as applicable.

Together, paragraphs (1) and (2) allow a single-family lot to host up to three state-protected units: a JADU inside the existing single-family dwelling or accessory structure, an ADU inside the same envelope or a converted accessory structure, and a new detached ADU up to 800 square feet with four-foot side and rear setbacks. Section 66314(d)(5) sets a separate statewide size ceiling of 1,200 square feet for a detached ADU, so the same single detached unit may be permitted at a larger size by the city under the Section 66314(d)(5) ceiling. A larger detached ADU under Section 66314(d)(5) is the same single detached unit on the lot, not a fourth state-protected unit, and a city ordinance that tries to count a Section 66314(d)(5) larger unit as an additional state-protected unit conflicts with the unit count in Section 66323(a).

• Section 66323(a)(1): one JADU plus one ADU within the existing or proposed space of a single-family dwelling or accessory structure.
• Section 66323(a)(2): one new construction detached ADU, four-foot side and rear setbacks, up to 800 square feet of livable space.
• Section 66314(d)(5) sets a 1,200 square foot size ceiling for the same single detached ADU, not an additional state-protected unit on the lot.

What state law allows on an existing multifamily lot

Government Code Section 66323(a)(3)(A) requires a local agency to ministerially approve multiple accessory dwelling units within the portions of existing multifamily dwelling structures that are not used as livable space, including storage rooms, boiler rooms, passageways, attics, basements, or garages, if each unit complies with state building standards for dwellings. Subparagraph (B) of the same paragraph requires a local agency to allow at least one accessory dwelling unit within an existing multifamily dwelling and to allow up to 25 percent of the existing multifamily dwelling units.

Government Code Section 66323(a)(4)(A) then addresses detached ADUs on the same lot as an existing or proposed multifamily dwelling, subject to a height limitation in subparagraph (A), (B), or (C) of paragraph (4) of subdivision (b) of Section 66321 and rear yard and side setbacks of no more than four feet. Clause (ii) of subparagraph (A) caps the number of detached accessory dwelling units at no more than eight on a lot with an existing multifamily dwelling, with the further limit that the number shall not exceed the number of existing units on the lot. Clause (iii) caps the number at no more than two on a lot with a proposed multifamily dwelling.

Subparagraph (B) of paragraph (a)(4) addresses the existing multifamily dwelling itself: if the existing multifamily dwelling has a rear or side setback of less than four feet, the local agency shall not require any modification of the existing multifamily dwelling as a condition of approving the application to construct an accessory dwelling unit that satisfies the requirements of the paragraph. That rule keeps pre-existing nonconforming setbacks from blocking an ADU application on the same lot.

What the JADU and ADU definitions require

Section 66333(d) requires a permitted JADU to be constructed within the walls of the proposed or existing single-family residence. For purposes of that subdivision, enclosed uses within the residence, such as attached garages, are considered a part of the proposed or existing single-family residence. Section 66333(a) limits the number of JADUs to one per residential lot zoned for single-family residences with a single-family residence built, or proposed to be built, on the lot.

Section 66333(b) requires owner-occupancy in the single-family residence if the JADU has shared sanitation facilities with the existing structure. The owner may reside in either the remaining portion of the structure or the newly created JADU. Owner-occupancy shall not be required if the JADU has separate sanitation facilities, or if the owner is another governmental agency, land trust, or housing organization. Section 66333(c) requires the recordation of a deed restriction that runs with the land, is filed with the permitting agency, prohibits the sale of the JADU separate from the sale of the single-family residence, and restricts the size and attributes of the JADU under the same article.

Section 66333(e) requires a permitted JADU to include a separate entrance from the main entrance to the proposed or existing single-family residence. If the permitted JADU does not include a separate bathroom, it shall include a separate entrance from the main entrance to the structure, with an interior entry to the main living area. These rules apply alongside the per-lot cap in Section 66323(a)(1), so a single-family lot with one JADU plus one ADU still has to satisfy both.

What Section 66325 does to conflicting local rules

Section 66325(a) states that Article 2 supersedes a conflicting local ordinance, except that local agencies may adopt less restrictive requirements. A city ordinance that tries to set a lower number of allowed ADUs or JADUs than Section 66323 allows conflicts with state law and is preempted. A city ordinance that allows more units than Section 66323 allows is less restrictive and is allowed. Section 66325(c) repeats the same point for Article 3 on JADUs.

Section 66323(b) reinforces the rule at the unit level: a local agency shall not impose any objective development or design standard that is not authorized by this section upon any unit that meets the requirements of any of paragraphs (1) to (4), inclusive, of subdivision (a). The combined effect is that the state sets the floor on how many ADUs a city must allow, and the city can only set standards that are less restrictive, not more restrictive.

Section 66323(c) carries the same rule into the application intake: a local agency shall not require, as a condition for ministerial approval of a permit application for the creation of an ADU or JADU, the correction of nonconforming zoning conditions. A nonconforming primary dwelling or nonconforming lot cannot be used to deny the ADU application, even when the ADU itself would meet state law.

How L Square confirms the per-lot count on real Orange County and Los Angeles County lots

L Square Design & Build's site review for a per-lot ADU count starts with the existing structure, the existing accessory structures, and the lot's existing or proposed single-family or multifamily status. On a single-family lot with one existing house, Section 66323(a)(1) allows one ADU and one JADU inside the existing envelope, and Section 66323(a)(2) allows one new detached ADU up to 800 square feet, for a total of three state-protected units. Section 66314(d)(5) sets a 1,200 square foot size ceiling for that same single detached unit; it is not a fourth state-protected unit. On an existing multifamily lot, Section 66323(a)(3) and (a)(4) set the inside-conversion and detached unit caps.

L Square's published 2026 model lineup runs from the 600 sq ft two-bedroom Model 600 at $180,000, to the 800 sq ft Models 800A and 800B at $240,000 each, to the 1,000 sq ft Models 1000A and 1000B at $295,000 each, up to the 1,200 sq ft Model 1200 at $354,000. The 600 and 800 square foot models fit Section 66323(a)(2) as the state-protected detached ADU on a single-family lot. The 1,000 and 1,200 square foot models use Section 66314(d)(5) as a larger size for the same single detached unit on the lot.

A 700 sq ft detached ADU with a vaulted ceiling built by L Square in Pasadena is documented on the project walkthrough page, with the finished great room, kitchen, bath, and bedroom shown. That unit sits within the 800 square foot Section 66323(a)(2) state-protected cap and the four-foot side and rear setbacks, so it was permitted through the standard ministerial process under State ADU Law. A completed 1,188 sq ft two-story ADU in Rosemead is documented on the second project walkthrough page, an example of how L Square works within the Section 66314(d)(5) 1,200 square foot size ceiling on the same lot as the primary dwelling.

For homeowners comparing the per-lot count across California, the right questions for the local agency are: (1) is this lot a single-family lot or a multifamily lot, (2) is the proposed or existing primary dwelling single-family or multifamily, and (3) is the local agency allowing up to the Section 66323(a) state-exempt cap or only less restrictive local rules. L Square Design & Build can be reached at (949) 374-7980 to discuss a specific lot in Orange County or Los Angeles County.