ADU rules in Milwaukie

A detached backyard ADU is allowed by right in both of Milwaukie's residential zones: Tables 19.301.2 (R-MD, moderate density) and 19.302.2 (R-HD, high density) list 'Accessory dwelling unit' as 'P', defined in the table key as 'Permitted/allowed by right'. The property's primary use must be a single detached dwelling, and up to 2 ADUs are allowed per site, of which at most one may be attached to or inside the house, so at least one detached unit is available in every configuration. Detached units are capped at 800 sq ft of floor area and 800 sq ft of footprint, 25 ft and 2 stories in height, with 5 ft side and rear yards and base-zone front and street side yards. They must also include at least 2 of 5 listed design details (covered porch, recessed entry, 12 in eaves, 3 to 7 in lap siding, 3 in window trim) and meet privacy standards for walls within 20 ft of a side or rear lot line.

Attached and internal ADUs are allowed by right under the same use-table entry and the same by-right approval path. MMC 19.910.1.E.1 lets an ADU be created by converting an existing structure, adding to an existing structure, building new, or combining an addition with a conversion, so basement, attic, and garage conversions all qualify. Attached units are capped at 800 sq ft, but that cap is expressly waived when the basement of a primary dwelling that has been on the site at least 5 years is converted. Design standards limit the front-facing facade to a single entrance, ban stairs, decks, and landings serving the ADU on that facade, and require new floor area to match the house in exterior finish, trim, window proportion and orientation, and eave projection. If a site has 2 ADUs, only one of them may be attached to or within the primary structure.

Both ADU types are capped at 800 sq ft of floor area, with no percentage-of-house limit in the current codified text. Detached units carry the additional dimensional caps in Table 19.910.1.E.4.b: 800 sq ft maximum structure footprint, 25 ft maximum height limited to 2 stories, 5 ft required side and rear yards, and base-zone front and street side yards. Two exceptions loosen the caps: the 800 sq ft limit does not apply to a basement conversion where the primary dwelling has stood at least 5 years, and converting an accessory structure legally established before June 3, 2022 (the effective date of Ordinance 2218) is exempt from the footprint, setback, and design standards, though not from the 800 sq ft floor area cap. A Type II variance can add up to 25% to an ADU's floor area and/or footprint. Building an ADU also raises the base-zone maximum lot coverage by 5 percentage points, an allowance that applies only to the ADU itself.

Nothing in MMC 19.910.1 requires the owner to live on the property. The by-right approval criteria in 19.910.1.D.1 are a closed list of five standards (allowed use in the base zone, single detached dwelling as the primary use, no more than 2 ADUs with at most one attached, compliance with the 19.910.1.E development standards, and compliance with the rest of Title 19), none of which mentions occupancy, and no covenant or deed restriction is required. State law reinforces this: ORS 197A.425(1)(b)(B) provides that 'reasonable local regulations relating to siting and design' for ADUs 'does not include owner-occupancy requirements of either the primary or accessory structure', and Milwaukie's population of roughly 21,000 puts it well over the 2,500 threshold in ORS 197A.425(1)(a). The only occupancy rule that touches ADUs applies to short-term rental use, not to owning or long-term renting the unit, and ORS 197A.425(2) expressly preserves local authority to require owner occupancy for vacation occupancies.

Milwaukie regulates off-street parking with maximums only, not minimums. Section 19.605 is titled 'Vehicle Parking Quantity Requirements' and its operative subsection 19.605.1 is 'Parking Maximums', providing that where parking is provided it may not exceed the figures in Table 19.605.1; the table's only value column is 'Maximum Allowed', and row A.5 'Accessory dwelling units (ADU)' reads 'No maximum.' Ordinance 2243, adopted May 21, 2024, deleted the former 'Minimum Required' column citywide; before that amendment the ADU row read 'No additional space required unless used as a vacation rental, which requires 1 space per rental unit', so even the superseded minimum did not apply to an ordinary ADU. ORS 197A.425(1)(b)(B) independently bars Oregon cities over 2,500 population from requiring additional off-street parking as a condition of ADU approval, so there is no state-law conflict to flag here.

ADUs are ministerial. MMC 19.910.1.C and .D.1 both state that an application to establish an accessory dwelling unit is 'allowed by right' provided the listed standards are met, and Table 19.901, the complete list of the city's land use applications, lists only Manufactured Dwelling Park (Type III) and Temporary Dwelling Unit (Type I or III) under 'Residential Dwellings: Section 19.910'. Accessory dwelling units appear nowhere in that table, so no land use application, notice, or hearing is triggered; the approval path is a building permit, with the city's attached or detached ADU worksheet submitted alongside it, plus engineering review and system development charges. Discretionary review is only reached if the applicant needs a variance (a Type II review for up to a 25% increase in ADU floor area or footprint, or for relief from the detached design details) or if a historic resource or natural resource overlay applies to the property.

Title 19 places no restriction on renting an ADU on a normal lease: there is no owner-occupancy requirement, no minimum lease term, and no cap on the number of rented units. Short-term rental (under 30 days) is regulated instead through the home occupation standards. MMC 19.507.5 allows a short-term rental as an accessory use to a primary residence only if the residence is occupied by the owner or a primary operator at least 270 days per year; where the property has an ADU, subsection C requires that either the house or the ADU be so occupied. Unhosted rentals are capped at 95 days per year, a property in a low-density residential zone is limited to one short-term rental at a time, no more than 2 rental parties may occupy a unit at once, and the operator must register with the city under Title 5. The Planning Division's short-term rental handout (Rev. 5/2026) confirms an ADU can be the rented unit and describes the business registration plus short-term rental permit and building inspection. A true 'vacation rental', defined in MMC 19.201 as a unit with no primary occupant or occupied under 270 days per year, is a conditional use in both R-MD and R-HD and needs a hearing.