ADU rules in Portland

Section 33.205.020 allows one detached ADU on a site with a house, attached house, or manufactured home in every residential zone (RF and R20 through R2.5) and in the multi-dwelling, commercial/mixed use, and EX zones. In R20 through R2.5 a second ADU is allowed when the lot meets the larger Table 205-2 minimum lot area (R20 12,000, R10 6,000, R7 4,200, R5 3,000, R2.5 1,500 sq ft) and fronts a maintained street; in multi-dwelling, C, and EX zones two ADUs are allowed regardless of lot size or frontage. When there are two ADUs, at least one must be detached. Detached ADUs must sit 40 feet back from the front lot line or behind the rear wall of the house, and must meet the base-zone accessory structure standards (20 ft maximum height, 15 ft if placed inside a side or rear setback in R7, R5, or R2.5).

The same allowance in 33.205.020 covers attached and internal ADUs: the code does not distinguish detached from attached for the first ADU on a site with a house, attached house, or manufactured home, and the city describes creating an ADU by converting part of the existing house, adding to it, or converting an accessory structure. Two limits matter. If a lot has two ADUs, at least one of them must be detached, so only one can be attached or internal. If the primary building is a duplex, the single allowed ADU must be detached from the duplex. Basement conversions get a bonus: the 800 sq ft / 75 percent size cap does not apply when a basement in a primary dwelling that has been on the site at least 5 years is converted to an ADU.

Section 33.205.040.C.1 caps ADU living area at 75 percent of the primary dwelling unit's living area or 800 square feet, whichever is less, so a 1,000 sq ft house supports a 750 sq ft ADU and anything above about 1,067 sq ft hits the flat 800 sq ft ceiling. Where the primary building is a duplex, the cap runs off the larger of the two units. Living area excludes exterior wall thickness, garages, basement space under 6 feet 8 inches of ceiling height, and space under 5 feet or not reached by a stairway. Detached ADUs are separately limited by the base-zone accessory structure rules: 20 feet maximum height, 15 feet (with 10 ft walls) if placed inside a side or rear setback in R7, R5, or R2.5, no more than 20 percent site coverage for all detached and connected covered accessory structures combined, and per-structure coverage no greater than the smallest primary structure's coverage or 900 square feet, whichever is greater.

Chapter 33.205 as codified through 10/1/24 has five sections (Purpose, Where ADUs are Allowed, General Requirements, Development Standards, Density) and contains no owner-occupancy standard; the word 'owner' does not appear in the chapter. State law also forecloses one: ORS 197A.425(1)(b)(B) says reasonable local siting and design regulations 'does not include owner-occupancy requirements of either the primary or accessory structure.' The one residency rule that does apply is narrower and is expressly preserved by ORS 197A.425(2): to run the ADU or the house as an accessory short-term rental, a resident (not necessarily the owner) must occupy a dwelling unit on the site at least 270 days per calendar year.

Chapter 33.205 imposes no parking standard on ADUs, and Chapter 33.266 no longer contains any minimum vehicle parking section at all: after the Parking Compliance Amendments Project (Ord. 191310, effective 6/30/23) the motor vehicle sections run 33.266.100 General Regulations, 33.266.110 Required Carpool and Electric Vehicle Parking, and 33.266.115 Maximum Allowed Parking Spaces, with minimums surviving only for bicycle parking in 33.266.200. The city's ADU zoning page states it plainly: 'No extra on-site parking is needed for an ADU.' ORS 197A.425(1)(b)(B) independently bars Oregon cities from requiring additional off-street parking as a condition of ADU approval, so there is no state-law conflict here.

An ADU that meets the Chapter 33.205 standards is allowed outright, with no land use review: the approval path is a building permit plus electrical, plumbing, and mechanical trade permits from Portland Permitting and Development, and the city publishes four free pre-approved detached ADU plan sets to shorten review. Discretion enters only by exception. If a development standard cannot be met, the applicant needs an Adjustment Review under Chapter 33.805, which the city describes as a discretionary land use review taking roughly 8 to 10 weeks with no guarantee of approval. In the Historic Resource overlay (33.445) an ADU must meet the Community Design Standards of 33.218 or go through Historic Resource Review, and several visitability standards in 33.205.040.C.4 are flagged 'Adjustments are prohibited.'

Nothing in Chapter 33.205 limits who may rent an ADU or for how long, and ORS 197A.425 bars an owner-occupancy condition, so month-to-month and longer tenancies are unrestricted. Short-term rental is a separate permit regime. Section 33.205.030 allows an ADU on a site with a Type A accessory short-term rental, and with a Type B ASTR if 33.815.040.B.1 is met. Under 33.207.040 a Type A ASTR is capped at 2 bedrooms and 5 guests, requires a resident to occupy a dwelling unit on the site at least 270 days per calendar year, and the resident may live in either the house or the ADU while renting bedrooms in either, but only 2 bedrooms site-wide; Type A permits must be renewed every two years, and Type B (3 to 5 bedrooms) is a conditional use. Separately, taking the ADU SDC waiver records a 10-year covenant that no structure on the property, including single bedrooms in the main house, may be short-term rented; revoking or violating it costs 150 percent of current SDCs. An ADU cannot be sold off separately, since 33.205.020 only allows one on a site that already holds a house, attached house, manufactured home, or duplex, and ORS 197A.420(4) treats a single-unit dwelling plus one ADU as a single unit for middle housing land division purposes.