ADU rules in Westminster

Detached ADUs are allowed with an existing or proposed single-family or multifamily home in every zone that allows residential development: the residential use table lists 'Accessory dwelling units and junior accessory dwelling units' as permitted (P) in R1 through R5 (WMC 17.210.010, Table 2-2), the mixed-use (MU) zone table, as amended by Ord. No. 2634 (adopted May 13, 2026), lists them as P, and 17.400.135.C.1 extends this to specific plan and mixed-use zones on lots with a residence. A new detached ADU needs 4-foot side and rear setbacks plus the zone's front setback, 6 feet of separation from the house and other detached accessory structures on a single-family lot (10 feet from other dwellings on a multifamily lot), siding and roof that match the main home, shielded lighting and no encroachment into easements (17.400.135.L.5, L.6, L.9). The codified count rule still reads 'only one ADU or JADU' on a single-family lot except under the state-exempt pathway (C.3.a), which itself allows a detached new-construction unit of up to 800 sq ft with 4-foot setbacks combined with a JADU (N.1.b); Gov. Code 66323(a), as amended by SB 543 effective January 1, 2026, requires approval of 'any combination' of the exempt units, and the clerk's video index of the August 26, 2026 City Council meeting records the Community Development Director saying the city follows state law, with a limit of two ADUs and one JADU. On a lot with an existing multifamily building up to eight detached ADUs are allowed, never more than the number of existing units, and two with a proposed multifamily building (N.1.d-e).

Attached ADUs (additions physically attached to the home) and converted ADUs (all or part of the existing interior space of a dwelling or accessory structure, including attached or detached garages) are allowed on the same residential lots (17.400.135.B.2-B.4, C.4). Converted space needs no new setbacks (L.5.a), and under the state-exempt pathway one ADU and one JADU may be created within the existing or proposed space of a single-unit dwelling or accessory structure, with an accessory structure allowed to grow by up to 150 sq ft for ingress and egress (N.1.a). An attached ADU may be up to 25 feet or the zone's height limit, whichever is lower, and no more than two stories (L.1.a.iv); an ADU inside the second floor of a home may not have exterior stairs (L.7.a). A JADU of up to 500 sq ft may be created within a single-unit dwelling, including an attached garage, on a lot zoned for single-family use, with an efficiency kitchen and a separate entrance on a different side of the home than its front door (C.2, M.1-M.3, M.8.b); the single-family-zone limit follows HCD's December 18, 2023 letter to the city. In existing multifamily buildings, ADUs may be converted from non-livable space such as storage rooms, attics, basements or garages: at least one, and up to 25 percent of the existing units (N.1.c).

A detached ADU may have up to 1,200 sq ft of floor area (17.400.135.L.4.b). An attached ADU is capped at 1,200 sq ft or 50 percent of the living area of the primary dwelling, whichever is less, but 850 sq ft is always allowed for a studio or one-bedroom unit and 1,000 sq ft for a unit with more than one bedroom (L.4.a). An ADU converted entirely within an existing structure has no size cap, and when a larger new home is built the whole existing house may be converted to an ADU (L.4.c-d); the state-exempt detached unit is capped at 800 sq ft and a JADU at 500 sq ft (N.1.b, M.8.b). Heights: 16 feet for a detached ADU, 18 feet within one-half mile walking distance of a major transit stop or high-quality transit corridor (plus 2 feet to match the home's roof pitch) or on a lot with a multistory multifamily building, and 25 feet or the zone limit, whichever is lower, for an attached ADU, two stories maximum (L.1.a). Since Ord. No. 2628 every ADU counts toward the zone's lot coverage (40 percent in R1, WMC 17.210.015 Table 2-3), and zone standards are waived only as far as needed for an 800 sq ft ADU (L.2, L.12), so on small lots coverage can hold a non-exempt ADU near 800 sq ft. The Council kept the 1,200 sq ft cap in November 2025 although the September 24, 2025 staff report offered a 1,000 sq ft option for units with more than one bedroom. 'Floor area' means gross floor area measured from the interior face of exterior walls and counting partitions, stairways and mechanical rooms (17.700.010), while Gov. Code 66321(b) measures the state size floors in interior livable space; the city's pre-approved plans are sized by net interior area (748 to 1,198 sq ft).

Section 17.400.135 imposes no owner-occupancy requirement on ADUs, and Gov. Code 66315 bars one ('No additional standards ... shall be used or imposed, including an owner-occupant requirement'). JADUs differ on paper: the codified deed restriction still requires, for every new JADU, that 'the owner must reside either in the primary dwelling or in the JADU' unless the owner is a government agency, land trust or housing organization (M.8.d), and the June 2025 application packet (PL-117) repeats that rule. Ord. No. 2628 was adopted November 12, 2025, before AB 1154 took effect on January 1, 2026; Gov. Code 66333(b) now allows owner occupancy to be required only when the JADU shares sanitation facilities with the main home, and 17.400.135.A.2 makes mandatory state law control over conflicting local text. So a JADU with its own bathroom carries no owner-occupancy condition, while one that shares a bathroom still does; the pending Zoning Code rewrite (Case No. 2026-0053) would codify the shared-sanitation rule.

One off-street space is required for an ADU in addition to the home's own parking, unless the ADU has no bedroom (a studio), and it may be provided as tandem parking on a driveway (17.400.135.L.11.a); the citywide parking table simply refers ADUs to this section (WMC 17.320.020). No space is required when the ADU is within one-half mile walking distance of public transit such as a bus stop, within an architecturally and historically significant district, part of the proposed or existing home or an accessory structure, where on-street permits are required but not offered to the occupant, within one block of a car-share vehicle, or applied for together with a new home that meets one of those tests (L.11.b, mirroring Gov. Code 66322(a)). Garages, carports and covered or uncovered spaces demolished or converted for an ADU need not be replaced (L.11.c), JADUs need no parking (M.5), and units on the state-exempt pathway are free of the section's other objective standards, parking included (N.1). Lots with an ADU or JADU may widen the driveway by 5 feet (WMC 17.300.020.D.2).

ADUs and JADUs are approved ministerially: a complete application must be approved or denied within 60 days, or 30 days for a city pre-approved plan or a plan identical to a detached ADU approved in the current building-code cycle, and it is deemed approved if the city does not act (17.400.135.D.1, D.1.e-f); state-exempt units must be approved ministerially on a building permit (N.1). The city runs a combined Planning zoning clearance and Building plan check, filed with the Building Division in person or through the Westminster Build online portal (application packet PL-117), and ADUs and JADUs are exempt from Development Review (WMC 17.520.010.C.1). Gov. Code 66317 adds the 15-business-day completeness determination, which the local text does not yet carry. The city offers free pre-approved detached ADU plans in six layouts from 748 to 1,198 sq ft (net interior area); they are not pre-permitted and may not be used in a flood zone or for projects that also include a JADU, a room addition, corrections of unpermitted work or a new garage.

The ADU section says ADUs and JADUs 'may not be rented for periods of less than 30 days' (17.400.135.I, with the same rule for state-exempt units in N.3 and in the JADU deed restriction, M.8.c), but Westminster's citywide short-term rental ban (Chapter 9.74, Ord. No. 2566 of 2020) makes it unlawful to rent or advertise any residential dwelling, dwelling unit or room for 'transient use', defined as rental 'for a period of thirty days or less' (9.74.010, 9.74.020; zoning cross-reference 17.200.020.G), so in practice an ADU or JADU must be rented for 31 days or more; hosting platforms may not complete booking transactions for residential property (9.74.030), and the city's ADU application packet says the same ('30 days or less'). State law requires terms longer than 30 days for JADUs and state-exempt 66323 units anyway (Gov. Code 66333(g), 66323(e)); for an ordinary ADU, Gov. Code 66315 lets a city require terms of 30 days or longer, so the citywide ban sits one day past that floor. An ADU may not be sold or conveyed separately from the main home except through a qualified nonprofit under Gov. Code 66341 (17.400.135.H); Westminster has not opted into the Gov. Code 66342 ADU-condominium regime. The code has no rental registration or rent stabilization program.