Aumsville

Oregon has the most comprehensive statewide ADU preemption framework in the country after California. House Bill 2001 (2019), codified principally at ORS 197.312(5), requires every Oregon city of more than 2,500 residents inside an urban growth boundary, and every Oregon county with population over 15,000, to allow at least one accessory dwelling unit (interior, attached, or detached) by right for each existing or newly-constructed single-family detached dwelling on residentially-zoned lots. Local jurisdictions may impose 'reasonable regulations' on siting and design but may NOT require owner-occupancy of either the primary or accessory unit and may NOT require additional off-street parking. Senate Bill 458 (2021), codified at ORS 92.031, authorizes 'middle housing land divisions' that allow each unit of a duplex / triplex / quadplex / townhouse / cottage cluster to be partitioned onto its own lot for fee-simple sale via an expedited land-division process; SB 458 does not directly add an ADU mandate but interacts with HB 2001 because an existing ADU can be split off onto its own lot under SB 458's expedited process (although a new ADU cannot be created after a SB 458 division). HB 2001 also separately preempts single-family-only zoning in cities over 25,000 by mandating duplexes statewide (and triplexes, quadplexes, townhouses, and cottage clusters in larger cities), which is the 'middle housing' provision discussed alongside ADUs in DLCD guidance.

• ORS 197.312(5) — Limitation on city and county prohibitions on accessory dwelling units — The codified ADU preemption provision originating in HB 2001 (2019). Requires cities >2,500 within an urban growth boundary and counties >15,000 to allow at least one ADU by right per single-family detached dwelling on residentially-zoned lots. Bars owner-occupancy mandates and additional off-street parking requirements; allows reasonable siting and design regulations.
• ORS 197.758 — Middle housing in lower density residential zones (HB 2001 'middle housing' codification) — Companion to the ADU provision. Mandates that cities >25,000 allow duplexes, triplexes, quadplexes, townhouses, and cottage clusters in residential zones; cities 10,000-25,000 must allow duplexes. Operative January 1, 2020 with municipal compliance deadline July 1, 2021 (cities <25k) or July 1, 2022 (cities >25k).
• ORS 92.031 — Middle housing land divisions (SB 458 (2021)) — Authorizes expedited land divisions that put each middle housing unit on its own lot for fee-simple sale. Applies to middle housing land divisions submitted on or after June 30, 2022. Existing ADUs may be split off via SB 458; new ADUs may not be created after a SB 458 division.
• House Bill 2001 (2019) Enrolled — 80th Oregon Legislative Assembly — Session law text amending ORS 197.312 and creating the middle housing mandate. Effective August 8, 2019; ADU and middle housing provisions operative January 1, 2020 with municipal compliance windows running through 2022.
• Senate Bill 458 (2021) A-Engrossed — 81st Oregon Legislative Assembly — Session law text adding the middle housing land division to ORS Chapter 92. Effective June 23, 2021; operative for applications on or after June 30, 2022.

Oregon's state-level ADU policy infrastructure is concentrated in the Department of Land Conservation and Development (DLCD), which publishes guidance documents for cities and counties implementing ORS 197.312(5) and ORS 197.758, runs the Housing Choice and Middle Housing technical-assistance programs, and audits municipal compliance with HB 2001. Oregon does not currently maintain a statewide pre-approved ADU plan catalog (those exist at the city level, e.g. Portland's pre-approved ADU plans), and there is no statewide impact-fee waiver, no statewide streamlined-review timeline floor beyond the reasonable-regulation requirement of ORS 197.312(5), and no state ADU rebate program.

• DLCD ADU implementation guidance — Statewide guidance to local governments on what 'reasonable regulations' on ADU siting and design under ORS 197.312(5) means in practice. Updated September 2019 to coincide with HB 2001 enactment.
• DLCD Housing Choice / Middle Housing technical assistance — Ongoing TA program that supports cities and counties in updating development regulations to comply with HB 2001 (ADUs and middle housing) and SB 458 (middle housing land divisions).