ADU rules in Tigard

Tigard allows one detached ADU per lot outright in every zone that permits detached houses. Table 18.110.3 lists Accessory Dwelling Units (Chapter 18.220) as 'Y, allowed' in the RES-A, RES-B, RES-C and RES-D zones; the only residential zone that prohibits them is RES-E, the apartment zone where new small form residential construction is not allowed at all. Chapter 18.220 is written as clear and objective standards, so a compliant unit is approved through the building permit rather than a hearing. The limits that bite are structural rather than discretionary: a detached ADU is allowed only on a lot with small form residential development (a house, duplex or triplex) and is prohibited as an accessory to apartment, cottage cluster, courtyard unit, quad and rowhouse development.

Attached and internal ADUs are not regulated by the ADU chapter at all. Since Ordinance 22-06 the code folds them into 'small form residential development', defined in Section 18.30.020 as one detached house or up to three attached dwelling units on a lot, and regulates them under Chapter 18.290. Small Form Residential is a 'Y, allowed' housing type in RES-A through RES-D (Table 18.110.3) and in the MUR commercial zone (Table 18.120.2). A basement conversion, an internal split or a garage-loft addition is therefore allowed outright and is checked against the clear and objective standards of Section 18.290.040 when the building permit is reviewed.

Section 18.220.040.B caps a detached ADU at 800 square feet and Subsection C caps its height at 25 feet. Setbacks match the base zone standards for small form residential, except that a detached ADU may sit within five feet of the rear property line if it is 15 feet or less in height and may never be closer to the front line than the primary dwelling. Section 18.40.120 counts a garage attached to the detached ADU inside the 800 square feet and, where the unit sits above a detached garage, measures the combined structure against the 25-foot cap; converting an existing garage counts the whole structure, including any part still used as a garage. Attached and internal ADUs fall under Chapter 18.290, which sets no floor-area limit at all: they are bounded instead by the base zone's 80 percent maximum lot coverage, 20 percent minimum landscape area and maximum building height (30 feet in RES-A and RES-B, 35 feet in RES-C and RES-D). Either way the lot may hold no more than three dwelling units in total, counting the detached ADU.

Nothing in Title 18 conditions an ADU on the owner living on the property. A full-text read of the entire development code turns up 'owner-occupied' only once, in the aspirational purpose statement at Section 18.110.010.A. That matches state law: ORS 197A.425(1)(b)(B) excludes 'owner-occupancy requirements of either the primary or accessory structure' from the reasonable siting and design regulations a city may impose, and Tigard's population is far above the statute's 2,500 threshold, so the mandate binds. The only occupancy-adjacent string attached to a Tigard ADU is voluntary and fee-related rather than zoning: an ADU that takes the city's SDC exemption records a covenant barring short-term rental use for ten years (TMC 3.24.180.A).

Section 18.220.010.E states outright that detached ADUs 'require no additional off-street parking', and neither Chapter 18.220 nor Chapter 18.290 sets any parking quantity standard. Tigard then went further than the ADU exemption: Ordinance 22-10 (parking reform compliance) and Ordinance 23-08 rewrote Chapter 18.410 so that Table 18.410.3 now sets only the maximum number of off-street vehicle spaces allowed, not minimums, meaning no development in the city carries a parking minimum. ADUs are also exempt from the minimum bicycle parking standards in Section 18.410.050.A. All of this is consistent with ORS 197A.425(1)(b)(B), which bars cities from requiring additional off-street parking as a condition of ADU approval.

An ADU needs no land use application in Tigard. Table 18.710.1, the code's complete list of land use application types, contains no entry for accessory dwelling units or small form residential, and Section 18.780.040 requires site development review only for apartments, mobile home parks, alternative-standard cottage clusters and courtyard units, nonresidential and mixed-use development, and certain wireless facilities. Chapters 18.220 and 18.290 are framed as clear and objective standards, so compliance is confirmed through the building permit (with mechanical, plumbing and electrical permits as needed). Discretionary review only enters through an unrelated overlay, for example sensitive lands review under Chapter 18.510 or historic resource review under Chapter 18.755, or if an applicant asks for an adjustment to a standard under Chapter 18.715.

Renting the ADU on a month-to-month or longer basis is a Residential Use, allowed outright wherever ADUs are allowed: Section 18.60.040.A.3 defines residential occupancy as 'arranged on a month-to-month basis, at a minimum, or for longer periods of time.' Renting it for shorter stays is not. Section 18.60.060.B classifies short-term rentals and bed-and-breakfast establishments as Commercial Lodging, defined as for-profit shelter where tenancy is typically less than one month, and Table 18.110.2 lists Commercial Lodging as 'P, prohibited' in RES-A through RES-E. Commercial Lodging is allowed only in the COM, MUC, MUE and MUR commercial zones (Table 18.120.1), and of those only MUR also allows ADUs. On top of the zoning ban, any ADU that used the city's SDC exemption carries a recorded covenant barring short-term rental for ten years after final inspection (TMC 3.24.180.A). Tigard's 2.5 percent local transient lodging tax (TMC Chapter 3.85) reaches lodging where it is lawfully offered; there is no ADU rental licensing regime and no cap on long-term rentals.