ADU rules in Downey

Downey makes ADUs a permitted use on lots with an existing or proposed home in the R-1, R-2, R-3, R-3-O and M-U zones and anywhere else single-family or multifamily housing is allowed (§ 9414.06). A single-family lot may have up to two ADUs, one new-construction attached or detached unit plus one conversion, plus one JADU (§ 9414.08(a)); a lot with an existing multifamily building may add up to eight detached ADUs but no more than the number of existing units, and a lot with a proposed multifamily building two (§ 9414.10(a)). A vacant lot can add an ADU only together with a new home (§ 9414.06(a)(2)). New detached units need 4-foot side and rear setbacks and may be 16 feet tall, or 18 feet plus 2 feet for a matching roof pitch within one-half mile walking distance of a major transit stop or high-quality transit corridor.

Attached additions and conversions of existing space (attached garages, storage areas, accessory structures) are allowed on single-family lots; conversions of permitted space carry no size cap and may expand up to 150 sq ft for ingress and egress (§ 9414.08(b)(6)). One JADU of up to 500 sq ft of interior livable space may be carved out of a single-family home, but JADUs are barred on multifamily-zoned properties (§ 9414.06(a)(1), § 9414.08(a)(2)). On multifamily lots, new ADUs must be detached from the multifamily building, while conversions of non-livable space inside it are allowed for at least one unit and up to 25 percent of the existing units (§ 9414.10(a)). Attached ADUs may be 25 feet tall or the zone's height limit, whichever is lower, and no ADU may exceed two stories (§ 9414.08(d)(3)).

Section 9414.08(b)(1) caps a new detached or attached ADU at 850 sq ft for a studio or one bedroom and 1,000 sq ft for two or more bedrooms, the same caps on single-family and multifamily lots (§ 9414.10(b)(1)). An attached ADU is further limited to 800 sq ft or 50 percent of the existing home, whichever is more, never above 1,000 sq ft (§ 9414.08(b)(2)). An ADU of 800 sq ft or less is exempt from FAR, lot coverage, front setback, design and open-space standards, while larger units must also meet the zone's lot coverage and FAR (§ 9414.08(b)(3)-(4)). Conversions of permitted space are uncapped and JADUs are limited to 500 sq ft of interior livable space. The headline numbers match the state floors in Gov. Code 66321(b)(2), although the local text still says 'floor area' rather than interior livable space (see caveats).

Downey imposes no owner-occupancy requirement on ADUs, consistent with Gov. Code 66315. Ord. 26-1544 (adopted 6-9-2026) narrowed the JADU rule so that owner occupancy, backed by a deed restriction recorded before final inspection, applies only when the JADU shares sanitation facilities with the main home (§ 9414.08(a)(2)(vii), § 9414.14(f)), matching Gov. Code 66333(b) as amended by AB 1154; government agencies, land trusts and housing organizations are exempt. The city's September 2025 R-1 fact sheet still describes a universal JADU owner-occupancy deed restriction and is out of date on this point.

Section 9414.14(a)(1) requires one uncovered off-street space for each ADU, which may sit on the existing legal driveway in setback areas or in tandem, unless the ADU is within one-half mile walking distance of public transit, in an architecturally and historically significant historic district, part of the home or an accessory structure, in an area where on-street permits are required but not offered to the occupant, within one block of a car share stop, or filed with a new home and otherwise meeting one of those criteria; the list mirrors Gov. Code 66322(a). JADUs need no parking (Gov. Code 66334(a)), and spaces lost to a garage conversion need not be replaced (Gov. Code 66314(d)(11)). On a plain reading the one-space rule exceeds Gov. Code 66314(d)(10)(A) for studio ADUs (one space per unit or per bedroom, whichever is less) and cannot be imposed on a state-exempt unit under Gov. Code 66323(b).

ADU and JADU permits are approved ministerially without discretionary review or a hearing (§ 9414.16(a)) and must be acted on within 60 days of a complete application or are deemed approved (§ 9414.16(b)); a denial must list the deficient items within the same period (§ 9414.16(c)). Plans are filed electronically through the city's Accela Citizen Access portal for Building and Safety and Planning review, and a demolition permit for a detached garage being replaced by an ADU is issued with the ADU permit (§ 9414.16(d)). Objective design standards (front entrance toward the street, matching roof slope and materials, frosted second-story windows, enclosed staircases) apply to ADUs and JADUs except new units of 800 sq ft or less and units built under Gov. Code 66323 (§ 9414.08(b)(3)-(4), § 9414.12).

ADUs may be rented long term but never for a term shorter than 30 days, regardless of when the ADU was built (§ 9414.14(c)), a floor Gov. Code 66315 allows for ordinary ADUs. State law requires terms longer than 30 days for state-exempt units (Gov. Code 66323(e)) and JADUs (Gov. Code 66333(g)), which the local text does not mention. ADUs may not be sold or conveyed separately except as Gov. Code 66341 requires (§ 9414.14(d)), so there is no 66342 condominium opt-in. Downey has no short-term rental permit or registration program: § 9158 defines 'Short-Term Rental' as occupancy of 30 consecutive days or less, but no regulation uses the term, and § 9312.08(b)(1) bars commercial use of residential lots.