ADU rules in Vista

Detached ADUs are permitted in the R-1-B, R-1, E-1, A-1, O-R (open space residential overlay), R-M and M-U zones and in specific plan areas that allow one-family dwellings by right (the city's July 2025 FAQ says specific plans that allow residential uses by right, and the Mar Vista Specific Plan adopted by Ord. 2025-09 allows ADUs under Chapter 18.31). On a single-family lot the code allows one detached new-construction ADU with 4-foot side and rear setbacks, which may be paired with a JADU; Gov. Code 66323(a), as amended by SB 543 effective 1-1-2026, also requires the city to approve it in combination with a converted ADU. On a lot with an existing multifamily building, § 18.31.040.B.1 still caps detached ADUs at two, but 66323(a)(4) allows up to eight (never more than the existing unit count, two beside a proposed multifamily building), and the city's July 2025 FAQ already applies the eight-unit figure. Approval is ministerial (see permitType).

Attached additions, ADUs within the proposed space of a new home, conversions of existing space in the home or an accessory building (with up to 150 sq ft of expansion for ingress and egress), and ADUs built as a second story over the home or over a detached garage or guesthouse are all allowed; a conversion of existing space is permitted on any lot in a zone that allows one-family or multiple dwellings by right. Existing multifamily buildings may convert non-livable space (storage rooms, attics, basements, garages) into at least one ADU and up to 25 percent of the existing unit count. A JADU of up to 500 sq ft must sit entirely within an existing one-family dwelling with its own entrance and an efficiency kitchen, one per lot, and JADUs are not permitted on lots with multiple dwellings. The July 2025 FAQ adds that stacked ADUs (one ADU atop another) are not permitted, a rule the code text does not state.

Section 18.31.050 caps attached and detached new-construction ADUs at 850 sq ft of floor area with fewer than two bedrooms and 1,200 sq ft with two or three bedrooms (no more than three bedrooms, Ord. 2024-02), and an attached ADU may not exceed 50 percent of the home's floor area, though Gov. Code 66321(b)(3) guarantees at least 800 sq ft of interior livable space whatever the percentage. Conversions of an existing accessory building or part of the home have no size limit, a JADU is capped at 500 sq ft, and every unit needs at least 150 sq ft; the code does not define how 'floor area' is measured, while the state floors are stated in interior livable space. The codified copy of § 18.31.050.A.1 prints the detached cap as '1,200 square feet if it has two bedrooms', but the signed Ord. 2024-02 (adopted 3-26-2024) and its staff report say 'two or three bedrooms', matching §§ 18.31.040.A.2.b and 18.31.050.A.2, so the adopted text governs. Section 18.31.070 holds every ADU to one story and 16 ft (a second-story unit is measured from the existing first-floor ceiling), which yields to 66321(b)(4): 25 ft for an attached ADU (R-1 and R-M allow 35 ft and two stories), 18 ft plus 2 ft for matching roof pitch for a detached ADU within half a mile walking distance of a major transit stop or high-quality transit corridor, and 18 ft beside a multistory multifamily building.

Chapter 18.31 imposes no owner-occupancy requirement on ADUs, and Gov. Code 66315 bars one (the city's August 2024 FAQ said ADUs are not subject to owner occupancy). For JADUs, § 18.31.100.A still requires the owner to live in the main home or the JADU in every case, backed by a recorded deed restriction (§ 18.31.100.F), and both city FAQs repeat that rule. Since 1-1-2026, Gov. Code 66333(b) as amended by AB 1154 allows an owner-occupancy requirement only where the JADU shares sanitation facilities with the home, and never where the owner is a governmental agency, land trust or housing organization, so the universal local clause is overridden for JADUs with their own bathroom. The deed restriction barring separate sale of a JADU and fixing its size remains valid under 66333(c).

Section 18.31.080.A requires one additional covered or uncovered space per ADU on top of the zone's residential minimum, which may be tandem on the paved driveway or on a side or rear yard driveway unless the Building Official finds that infeasible. No space is required within one-half mile walking distance of public transit (defined to include bus stops), within an architecturally and historically significant historic district, for a unit within the footprint of the proposed or existing home or accessory building, where on-street permits are required but not offered, or within one block of a car share vehicle; a JADU in an attached garage needs no replacement space. State law narrows the rule further: 66314(d)(10)(A) caps parking at one space per unit or per bedroom, whichever is less (none for a studio on a plain reading), and 66323(b) bars any parking standard on units approved under the state-exempt pathway, such as an 800 sq ft detached unit with 4-foot setbacks. Section 18.31.080.B.1 still requires replacing uncovered spaces an ADU eliminates, but AB 1170 added uncovered parking spaces to the 66314(d)(11) ban on replacement parking from 1-1-2026, so that clause is overridden. The city's July 2025 FAQ dropped its parking answer, and how staff apply these state overrides is undocumented.

An ADU or JADU application that meets the chapter's standards is reviewed and approved ministerially by the Community Development Department within 60 days of a complete application and is deemed approved if the city does not act (§ 18.31.120.B); the submittal is a site plan, floor plan and elevations with the building permit application, and Gov. Code 66317 adds the 15-business-day completeness determination and bars any hearing. When an ADU is applied for together with a new home, the city may hold the ADU decision until it acts on the home, but the ADU review stays ministerial (§ 18.31.120.C). Some lots first need grading clearance from the Land Development Engineering Division, and septic lots need San Diego County Health Department clearance, before building plans are accepted. Four pre-approved plans (499 to 1,149 sq ft) waive plan-check fees on lots with an existing single-family home.

ADUs and JADUs may be rented, but §§ 18.31.030.C and 18.31.100.E set a minimum rental term of no less than 30 consecutive days, which Gov. Code 66315 allows for ordinary ADUs; for JADUs (66333(g)) and units approved under the state-exempt pathway (66323(e)) state law requires terms longer than 30 days, one day more than the local text. Rentals of 30 consecutive days or less need a short-term rental permit, a business license and TOT registration under VMC Chapter 8.34 (Ord. 2024-05, adopted 5-28-2024, program effective 7-1-2024), whose definition expressly excludes 'any accessory dwelling unit permitted under Chapter 18.31', and the city's ADU and STR pages say STRs are not permitted in ADUs or JADUs. An ADU may not be sold separately except to a qualified buyer under the nonprofit provision (§ 18.31.030.B, citing legacy 65852.26, now Gov. Code 66341), a JADU may never be sold separately (§ 18.31.100.B and F), and the city has adopted no Gov. Code 66342 ADU-condominium ordinance.