ADU rules in Fullerton

Detached ADUs are permitted with an existing or proposed home on any lot where single-family or multifamily dwellings are allowed: Table 15.17.020(A) lists ADUs (including JADUs) in R-1, R-2, R-G, R-3R, R-3, R-4 and R-5, including the R-1P, R-2P and R-3P preservation variants, and 15.17.100(D) adds planned residential development districts, specific plan areas, lots where homes are conditionally permitted, and O-P (Office Professional) lots improved with a single-family home. The local track allows one ADU plus one JADU on a single-family lot, and R-1 or R-2 lots of at least one acre may have two detached ADUs (or one attached and one detached) if water and sewer capacity can support them. Separately, the city must ministerially approve a new detached unit of up to 800 sq ft with 4 ft side and rear setbacks under Gov. Code 66323, which state law lets an owner combine with a conversion ADU and a JADU. The R-MH (mobile home) zone does not list ADUs.

An ADU may be within, attached to, or detached from an existing or proposed single-family or multifamily home or accessory structure, including garages, and may be built above an existing lawfully constructed structure within the height limits. Units built inside an existing or proposed single-family home have no size cap, and one JADU of up to 500 sq ft is allowed within a single-family home (an attached garage counts), also on a lot that has an ADU. Conversions also qualify for the state-exempt path (one ADU and one JADU within existing or proposed space, with up to 150 sq ft of accessory-structure expansion for access), and converted garages need no replacement parking.

A detached ADU may not exceed 1,200 sq ft (a conversion of an existing accessory structure already larger than that keeps its size), and an attached ADU is capped at 850 sq ft for a studio or one bedroom and 1,000 sq ft for two or more bedrooms, with no percentage-of-home cap. ADUs inside a single-family home are uncapped, JADUs are limited to 500 sq ft, and an existing house of 1,200 sq ft or less may be redesignated as the ADU when a new home is built on the lot. Heights are 16 ft for a detached ADU, 18 ft within a half mile of a major transit stop or high-quality transit corridor (plus 2 ft to match the main roof pitch) or on a lot with a multistory multifamily building, and 25 ft or the zone limit, whichever is lower, for an attached ADU (two stories maximum). Lot coverage, FAR, open space, front setback and minimum lot size limits are waived as needed to allow an 800 sq ft ADU, and the state-exempt detached unit is capped at 800 sq ft. The code does not say how square footage is measured; since SB 543 the state floors of 850 and 1,000 sq ft are interior livable space, which the attached caps track exactly.

No owner-occupancy requirement applies to ADUs, and Gov. Code 66315 forbids one. The codified JADU deed restriction still requires the owner to live in either the primary dwelling or the JADU in every case, but since 1-1-2026 Gov. Code 66333(b) (as amended by AB 1154) permits that requirement only when the JADU shares sanitation facilities with the house, and 15.17.100(A)(4) lets mandatory state law control. A JADU with its own bathroom therefore carries no owner-occupancy duty, though the recorded deed restriction (no separate sale, size limit, binding on successors) still applies.

An ADU needs one off-street space in addition to the primary dwelling's parking unless it has no bedrooms (a studio needs none); the space may be tandem on the driveway and may sit in the front setback. No space is required when the ADU is within one-half mile walking distance of public transit (a bus stop counts), within a historic district or preservation zone, part of the existing or proposed home or an accessory structure, where on-street permits are required but not offered, within one block of a car-share vehicle, or applied for together with a new home on the lot. Garages, carports or open spaces removed or converted for an ADU need not be replaced, and JADUs need no parking. The state-exempt units in 15.17.100(H) carry no parking requirement because Gov. Code 66323(b) bars any standard that section does not authorize; the local text is silent on this point.

ADU and JADU applications are approved or denied ministerially within 60 days of a complete application (30 days for a city pre-approved plan or a plan identical to one approved in the current building code cycle), and an application not acted on within 60 days is deemed approved; the state-exempt units in 15.17.100(H) get a ministerial building permit in any residential or mixed-use zone. Section 15.17.100(A)(4) makes the ADU section prevail over conflicting Title 15 provisions, which matters because the general site plan triggers (15.47.020 for new construction in residential zones and 15.17.060(B)(2)(a) for new units in the R-1P, R-2P and R-3P preservation zones) would otherwise route ADUs to site plan review. Gov. Code 66317 bars discretionary review or a hearing for any ADU.

ADUs and JADUs may be rented long term but not for periods of less than 31 days, so neither can be used as a short-term rental; for the state-exempt units the 31-day floor matches Gov. Code 66323(e) and 66333(g) (terms longer than 30 days). For an ordinary local-track ADU the 31-day floor runs one day past Gov. Code 66315, which lets a city require only terms of 30 days or longer, and the JADU deed restriction separately says 30 days; both texts are recorded because the difference is a single day. ADUs may not be sold separately from the primary dwelling except under Gov. Code 66341 (qualified nonprofits) or 66342, and no FMC provision supplies the condominium-conveyance ordinance 66342 requires. The citywide short-term rental permit program (15.55.020(F)) is frozen for pending and new permits by urgency Ords. 3342 and 3346 until about 5-17-2027, and a single ADU rental owes no rental business tax (4.06.025(A) applies to four or more units).