ADU rules in Tualatin

A detached backyard ADU is permitted outright in the RL (Low Density Residential) and RML (Medium Low Density Residential) zones, which are the only two Tualatin zones where a detached single-family dwelling is allowed at all. TDC 73A.090(2)(a) states that an accessory dwelling unit is allowed in the RL and RML Zones, and the housing type tables at TDC 40.220 (Table 40-2) and TDC 41.220 (Table 41-2) list Accessory Dwelling Unit with status P, permitted outright. TDC 31.060 defines an ADU as an interior, attached or detached residential structure accessory to a single family dwelling, so a freestanding unit clearly qualifies. Limits: one ADU per lot or parcel, and the unit must be set back at least one foot from a line drawn parallel to the primary dwelling's main entrance.

Attached and interior ADUs are treated exactly like detached ones. TDC 31.060 defines an accessory dwelling unit as an interior attached or detached residential structure that is accessory to a single family dwelling, and TDC 73A.090 sets a single list of standards covering all three forms with no separate track or extra condition for a basement, garage or addition conversion. The city's ADU page repeats the same definition and routes every ADU, attached or detached, through the same Type I ADU Architectural Review. One wrinkle worth raising with staff: the siting rule at TDC 73A.090(2)(f), a one-foot setback from a line parallel to the primary dwelling's main entrance, is written for a distinct structure and the code grants interior conversions no exemption from it.

TDC 73A.090(2)(c) caps an accessory dwelling unit at 800 square feet of gross floor area, full stop: no per-zone split, no percentage-of-primary-dwelling formula, and no larger allowance for converting existing space. Gross floor area is defined at TDC 31.060 as the sum of the gross horizontal areas of the several floors of a building or structure measured from the exterior face of exterior walls, so exterior wall thickness counts toward the 800. There is no ADU-specific height rule; the unit takes the zone's general maximum structure height of 35 feet (Table 40-3 in RL, Table 41-3 in RML) and must fit the zone's setbacks (RL: 15 ft front, 5 ft side, 15 ft rear; RML: 10 ft front, 5 ft side, 10 ft rear) and lot coverage limits, which the city's ADU page states expressly.

No owner occupancy requirement, at application or afterward. TDC 73A.090(2) lists six ADU standards, (a) through (f), and none concerns who lives in either unit; the RL and RML zone chapters, the Architectural Review section and the city's ADU page are likewise silent. Oregon law independently forecloses one: ORS 197A.425(1)(b)(B) provides that reasonable local regulations relating to siting and design do not include owner-occupancy requirements of either the primary or accessory structure. Tualatin's population, about 27,000 by the city's own account, is far above the 2,500 threshold that triggers ORS 197A.425(1)(a). The statute's only escape hatch, subsection (2), lets a city require owner occupancy when it regulates vacation occupancies as defined in ORS 90.100; Tualatin does not allow short-term lodging in the zones where ADUs are permitted, so it has not used that hatch.

Tualatin requires no off-street parking for an ADU, and none for the single-family dwelling either. Chapter 73C was repealed and re-enacted by Ord. No. 1486-24 (June 10, 2024) as a maximums-only regime: TDC 73C.040(1) explains that Table 73C-1 lists the maximum permitted vehicle and minimum required bicycle parking, and no minimum vehicle parking standard for residential uses appears anywhere in the chapter. Table 73C-1 row (a)(i), Single-family dwellings and accessory dwelling units, reads None in both the Parking Zone A and Parking Zone B maximum columns (that is, no cap) and None Required for bicycle parking. State law bars a mandate regardless: ORS 197A.425(1)(b)(B) excludes requirements to construct additional off-street parking from the reasonable local regulations a city may attach to an ADU. Parking you choose to build still has to meet Chapter 73C design standards and the zone's 20-foot garage door setback.

Ministerial, staff-level approval. TDC 33.020(3)(e) puts development applications for an accessory dwelling unit that comply with the clear and objective standards in TDC 73A.090 on the Type I track, and TDC 32.210 defines a Type I procedure as a ministerial decision by the City Manager without public notice and without a public hearing, made on standards that require no discretion, final when signed. The sequence is an ADU Architectural Review with the Planning Division first, then structural, plumbing and mechanical permits from the Building Division, with the electrical permit filed separately with Washington County. Submittals are a land use application, a Clean Water Services service provider letter, a scaled site plan, elevations of all sides, and the fee. No conditional use permit, variance, neighborhood meeting or hearing is involved for a code-compliant ADU.

Nothing in the ADU standards limits renting, and an ADU is expressly a Household Living housing type under TDC 39.200(2), a category defined as the residential occupancy of an owner-occupied or rented dwelling unit. But that same section fixes the floor at 30 days: occupancy is long-term, 30 days or more, and non-transient, and TDC 39.200(3) provides that rentals of less than 30 days are classified as Commercial Lodging. Commercial Lodging does not appear in the RL use table (TDC 40.200 Table 40-1) or the RML use table (TDC 41.200 Table 41-1), and both chapters state that use categories which are not listed are prohibited within the zone. So an ADU in Tualatin can be a long-term rental but not a vacation rental. There is no ADU rental license or registration. The city does levy a transient lodging tax on transient lodging including dwelling units used for temporary human occupancy (TMC Chapter 9-09), but that is a revenue ordinance and does not authorize a lodging use in a residential zone.