ADU rules in Scappoose

Detached backyard ADUs are permitted outright. Every residential zone use table lists "Accessory Dwelling Units (ADU's) subject to the provisions of Chapter 17.92" as "Permitted outright": R-1 Low Density (17.44.030), R-4 Moderate Density (17.50.030), MH Manufactured Housing (17.54.030) and A-1 High Density (17.56.020). SMC 17.92.020(C) confirms the unit may be "construction of a new structure that is either attached or detached." Two limits matter: the ADU is allowed only on a parcel containing one single-family dwelling, and only one ADU per parcel (17.92.020(B)), so a duplex, triplex, quadplex or townhouse lot does not qualify. ADUs are also barred outright inside Cottage Housing Developments (17.58.100(5)), and the permitted-outright footnote applies only outside the Scappoose Creek Flood Plain.

Attached and internal ADUs are on exactly the same footing as detached ones; Chapter 17.92 draws no distinction. SMC 17.92.010 describes creating the unit "from existing space in the primary dwelling; a combination of existing and newly created space; space in an existing accessory building; or, from the addition of a new accessory building," and 17.92.020(C) allows creation "by converting existing living area or adding floor area, or construction of a new structure that is either attached or detached." One drafting trap: "An attached garage does not qualify as living area," so a garage conversion adds floor area rather than converting it. Two design standards apply to conversions and additions: only one entrance may sit on the front of the primary dwelling or a street-abutting facade unless the house already had more (17.92.020(E)), and siding, roofing and paint must generally match the primary dwelling (17.92.020(F)).

SMC 17.92.020(D): "The maximum gross habitable floor area (GHFA) of the ADU shall not exceed fifty percent of the GHFA of the primary residence on the lot, and shall not exceed a maximum of eight hundred square feet, whichever is less." The whichever-is-less test means a 1,200 sq ft house supports only a 600 sq ft ADU; you need a primary dwelling of at least 1,600 sq ft of habitable area to reach the 800 sq ft ceiling. Garage floor area is excluded from the calculation on both sides. Chapter 17.92 sets no separate height or setback standard, so a detached ADU is measured against the base zone's accessory building rules: 22 feet of height with five-foot side and rear setbacks behind the residence in both R-1 (17.44.050) and R-4 (17.50.050), against 35 feet for the principal building.

Chapter 17.92 contains no owner-occupancy standard, and a full-text search of the whole municipal code for "owner occupancy" and "owner-occupied" turns up nothing attached to ADUs (the only owner-occupancy language in the code is the bed and breakfast definition at 17.26.030). Nothing in the permitted-use tables or the site development review chapter adds one either. State law independently forecloses it: 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 that bar reaches every city over 2,500 population. The Census Bureau's 2024 population estimate for Scappoose is 8,282, so the city is well over the threshold. The one carve-out, ORS 197A.425(2), lets a city require owner-occupancy for vacation occupancies (short-term rentals); Scappoose has not adopted any such rule.

The printed local standard, SMC 17.92.020(G), reads: "The development of the ADU shall provide an additional on-site parking space if the primary dwelling has less than three on-site spaces (for example, inclusive of a garage and driveway) available before construction of the accessory unit." That text was last touched by Ord. 868 in 2018, a year before Oregon's HB 2001 (2019) added the parking bar, and the city has not amended Chapter 17.92 since. ORS 197A.425(1)(a) requires cities over 2,500 to allow at least one ADU for each detached single-unit dwelling inside the urban growth boundary in areas zoned for detached single-unit dwellings "subject to reasonable local regulations relating to siting and design," and (1)(b)(B) says those regulations do "not include ... requirements to construct additional off-street parking." Scappoose's 8,282 population (2024 Census estimate) puts it squarely over the line, so subsection G is void as a condition of ADU approval in single-family zones even though it remains on the books. The general parking table at 17.106.030(A)(1) (two spaces per dwelling unit for a single-family residence or duplex) is blocked by the same preemption as applied to an ADU. Because the void text is still printed, expect counter staff to quote it; raise ORS 197A.425 with the Community Development Center.

Ministerial. ADUs are "Permitted outright" in all four residential use tables (17.44.030, 17.50.030, 17.54.030, 17.56.020), and SMC 17.120.020(I) expressly exempts accessory dwelling units from Site Development Review, so there is no discretionary hearing and no planning commission review. The city's Building Department page for "Residential Remodels, Additions, Accessory Structures including Accessory Dwelling Units (ADU's)" states the whole process: "Permits are required. First ensure the ADU meets the City's ADU code 17.92." The Planning Department's own application list (annexation, conditional use, site development review, variance, zone change, home occupation and so on) contains no ADU application, confirming the path is a building permit with staff zoning review of setbacks, height and lot coverage. The one exception is the Scappoose Creek Flood Plain, where the permitted-outright footnote does not apply and a flood development permit under Chapter 17.84 is required.

Chapter 17.92 imposes no rental restriction at all, and 17.92.010 names "rental income to offset the costs of homeownership" as a purpose of the chapter, so a long-term tenancy needs no separate city approval and no owner-occupancy affidavit. Short-term renting is murkier. Scappoose has no short-term-rental license or registration chapter: a full-code search for "short-term rental" and "vacation rental" returns nothing on point, and Title 5 (Business Licenses and Regulations) has no such chapter. Stays of thirty days or less do fall under the Transient Room Tax, SMC Chapter 3.24: 3.24.010 defines "hotel" broadly as any structure occupied for transient occupancy of thirty days or less, 3.24.020 imposes a nine percent tax, and 3.24.060 requires the operator to register with the tax administrator within fifteen days of commencing business. The zoning side is the real obstacle: transient lodging is not a listed use in R-1, R-4, MH or A-1, and bed and breakfast (defined at 17.26.030 as owner-occupied, no more than two rental units, guest stays of five days or less) is only a conditional use in R-4, MH and A-1 and is absent from R-1 entirely. Confirm nightly rental with the Planning Department before listing an ADU. The code is silent on selling an ADU separately from the primary dwelling.