Do I need a permit for an accessory dwelling unit (ADU) in
Tualatin, Oregon?

Tualatin ADU permits — the key details

Oregon law (ORS 197.303-197.314) is the real zoning code now, and Tualatin's local ordinance exists mainly to administer the state mandate. Any single-family residential lot in Tualatin can have one detached ADU up to 800 square feet (or 75% of the primary dwelling's floor area, whichever is smaller) and one junior ADU (accessory dwelling unit inside or attached to the primary dwelling, max 499 sq ft). Setbacks are the same as the primary dwelling — typically 15 feet front, 10 feet side, 15 feet rear in R-7 zones — and the ADU must be owner-occupied OR rented; the state now allows either. No parking is required for the ADU itself (state preemption). However, Tualatin's plan-review staff will ask for parking documentation anyway; push back politely with OAR 660-033-0135, which says parking is NOT required. The City's building permit application is submitted through eTRAKiT (the online portal) or in-person at City Hall, 18125 SW Boones Ferry Road. Full building plans are required: foundation detail, framing plan, electrical plan (NEC), plumbing, HVAC, and egress plan per IRC R310 (required secondary exit from ADU bedrooms). Total permit fees are $5,000–$12,000, split as follows: base permit fee (1.5-2% of valuation, typically $1,500–$3,000 for a $100,000 ADU), plan-review deposit ($1,500–$3,000), and impact fees ($1,500–$2,500). Timeline is 8-14 weeks from application to occupancy permit, assuming no code violations on first review.

Detached ADUs trigger foundation and soil engineering scrutiny because Tualatin's underlying soil is volcanic and alluvial — some pockets contain expansive clay (particularly in south Tualatin near Durham and Sherwood). The city requires a geotechnical report if the lot slope is steeper than 10% or if soil borings indicate clay content above 15%. Frost depth in the Willamette Valley (Tualatin's west side) is 12 inches; footings must extend below that line per IRC R403.1.4.1, meaning 18-inch minimum depth in practice (6-inch safety margin). East of I-5 in Tualatin (toward Stafford and Gaarde roads), frost depth jumps to 24 inches. Slab-on-grade requires 12 inches of insulation (R-15 minimum, per IRC R402.2.7) if the ADU is heated; crawlspaces and basements are rare but require moisture control and radon mitigation per Oregon's radon code (OAR 333-123-2000, mandate in high-risk zones). If your lot is in the 100-year floodplain (FEMA map check first), the ADU must be elevated or built with flood vents, adding $3,000–$8,000 and extending review by 4-6 weeks. The City's GIS zoning map (available on Tualatin's website) shows floodplain and fire-risk overlays; check it before designing.

Egress is the non-negotiable sticking point for garage conversions and junior ADUs. IRC R310.1 requires at least one secondary exit from each sleeping area if the ADU has bedrooms. A detached one-bedroom ADU qualifies if the single window opening is at least 5.7 sq ft (operable) and the sill is no higher than 44 inches off the floor. A garage conversion with a second bedroom MUST have a second exit — either a door to the outside or another operable window meeting the same dimensions. Tualatin's building inspectors are thorough on egress; submitting plans without clear egress will trigger an automatic rejection and 2-week resubmission delay. Additionally, any ADU (detached or attached) with a kitchen (sink, stove, refrigerator) is classified as a dwelling unit and triggers full utility separation: separate electric meter, water meter, and sewer connection. Shared utilities are not allowed under OAR 660-033-0135 (state rule), though sub-metering is acceptable and costs $500–$1,500. If the ADU is junior (shares utilities with the primary dwelling), it CANNOT have a full kitchen — only a kitchenette (sink, microwave/cooktop, no full-size range). Tualatin's plan-review checklist explicitly flags this; submitting a junior ADU with a full kitchen will be rejected.

Owner-builder rules favor the homeowner in Oregon. If the primary-dwelling owner is building the ADU as owner-occupied (the owner lives in either the primary house or the ADU), the owner can pull the permit and do the work (though licensed contractors are still required for electrical, plumbing, HVAC, and gas). If the owner plans to rent the ADU immediately, the owner must hire a licensed general contractor (ORS 701.007). Tualatin's building department does NOT require a licensed contractor bond if the property owner is pulling the permit, but the owner bears liability for code compliance. Many homeowners hire a GC anyway to offload risk; expect $15,000–$30,000 in construction management on a $100,000–$120,000 ADU project. Plan review in Tualatin is typically completed in 3-4 weeks for straightforward detached ADUs; garage conversions and junior ADUs (which have tighter egress/utility constraints) often see 5-6 weeks. Foundation/framing inspections are back-to-back (1 week apart), rough trade inspections (electrical, plumbing, HVAC) are concurrent, and the final inspection often requires a third-party energy rater (blower-door test per Oregon's energy code, OAR 730-065-0100) — allow 2 weeks for that slot. Total time from 'first review comments' to occupancy permit is 10-14 weeks if you address comments cleanly.

Tualatin's ADU ordinance (Chapter 29.75 of the Tualatin Development Code) also requires ADU parking to be addressed in the site plan, but this is advisory only under state law — you can show zero ADU spaces and the City will approve it, though some inspectors will question it. If the primary lot is on a street with public parking (curbside spaces), the City may ask you to note that; don't treat this as a hard requirement. Junior ADUs (internal or very-close attached units) are common in Tualatin because lot sizes are modest (R-7 lots are often 8,000-10,000 sq ft) and detached ADUs eat up yard. A garage-conversion-plus-junior-ADU combo is allowed under state law (one detached OR one junior, not both) — clarify with your designer which route you're taking before submitting. Historic-district overlays do not apply to ADUs under Oregon state preemption (ORS 197.303), even if your lot is in Tualatin's Stafford-Tualatin Historic District or other local overlay. The City will flag this if your property touches a historic boundary; cite OAR 660-033-0100(2)(d) and you're clear.

Three Tualatin accessory dwelling unit (adu) scenarios

Oregon state ADU law vs. Tualatin's local rules — what actually binds

Oregon's ADU preemption (HB 2001, 2019, and HB 4127, 2023) strips away local zoning restrictions that cities like Tualatin used to enforce. Before 2019, Tualatin's code required ADUs to be owner-occupied, capped them at one per lot, and imposed parking and lot-size minimums. HB 2001 said: 'Nope, cities must allow at least one detached ADU (up to 800 sq ft or 75% of primary house, whichever is smaller) on any single-family-zoned lot.' HB 4127 (2023) added: 'And cities must also allow one junior ADU (internal or very close attachment, up to 499 sq ft) on the same lot.' Owner-occupancy is not required. Parking is not required (state rule OAR 660-033-0135 explicitly says zero ADU parking is allowed). Tualatin's current ordinance (Chapter 29.75 TDC) acknowledges this but still refers to the old language in places. The City's plan-review staff knows the state law overrides them, but they sometimes ask for 'parking justification' or 'owner-occupancy documentation' anyway — old habits. When this happens, cite OAR 660-033-0135(3)(d) (parking) or OAR 660-033-0100(1)(c) (owner-occupancy waived) and politely note that state law preempts local zoning. The City will not fight it, but they will note it in the file.

Frost depth, soil clay, and Willamette Valley foundation surprises

Tualatin straddles two foundation zones. West of I-5 (toward Sherwood, Durham, Stafford), frost depth is 12 inches; east of I-5 (toward Gaarde Road and the Stafford Ridge), it jumps to 24 inches. This is not intuitive — it's driven by elevation, drainage, and historical frost-heave data. Footings must go 6 inches below frost depth (safety margin), so west-side detached ADUs typically require 18-inch footings, and east-side ones need 30-inch footings. This adds 20-30% to foundation labor. Additionally, Tualatin's soils are volcanic (basalt bedrock) underlain by alluvial deposits from the Tualatin River and its tributaries. Clay content varies wildly lot to lot. South Tualatin (near Sherwood, around Avery Street and SW 124th) has pockets of Type CL and Type CH (expansive clay) from old river deposits. If your lot is in that zone and soil boring shows clay PI > 10%, the City will require a geotechnical report — non-negotiable, add $1,200–$1,500 and 2-3 weeks to plan review. The report will likely recommend either a spread footing (wider base, same depth) or post-tensioned slab-on-grade (can cost $3,000–$5,000 extra). Radon is also present in some Tualatin soil (volcanic areas are moderate-to-high risk). Oregon's radon code (OAR 333-123-2000) applies to all new buildings; the ADU must have radon mitigation if the lot is in a Zone 1 or Zone 2 county. Marion County (east Tualatin) is Zone 1; Washington County (west Tualatin) is Zone 2. Tualatin straddles both. The City's building department will ask: 'What's the radon map designation?' If you're unsure, check EPA radon zone map or the state's OHA radon database. Mitigation typically means a passive vent pipe from the slab to the roof (passive sub-slab depressurization per ASTM E2121); cost is $500–$1,000 and is shown on the framing plan.

Common questions