Everything homeowners ask about building an ADU in Eugene — answered with 2026 data.
Yes, ADUs are allowed in All residential zones, on a lot with a single primary dwelling; the city's ADU fact sheet (Form LU-230) and its ADU program page say ADUs are allowed in all neighborhoods. Lots in the urban growth boundary but outside city limits follow a separate fact sheet (Accessory Dwelling in UL Overlay). Contact Land Use (541-682-8336) for non-residential zones in Eugene, OR. The maximum size for a detached ADU is 800 sq ft or 10% of lot area, whichever is smaller, measured at the exterior walls and including halls, closets, stairs and baths (EC 9.2751(17)(a)1). Up to 300 sq ft of attached unheated garage or storage is not counted (800 sq ft if the ADU is above a garage). In the R-1 zone inside Amazon Neighbors, Fairmount Neighbors or South University: 600 sq ft on lots under 9,000 sq ft, 800 sq ft on lots of 9,000 sq ft or more (EC 9.2751(17)(c)2). Attached ADUs can be up to Same cap: 800 sq ft or 10% of lot area, whichever is smaller. Eugene has an ADU-friendliness score of 8/10. Check our full Eugene ADU rules page for complete zoning details.
ADU construction in Eugene typically costs $110,000-$285,000. The cost per square foot averages $150-$300. Garage conversions are more affordable at $60,000-$150,000, while prefab ADUs cost $90,000-$230,000. Permit fees add Valuation-based: building permit $953.34 plus $4.34 per $1,000 over $100,000, plan check 65% of that (waived for pre-approved plans), electrical $244.40, plumbing $571.40 for one bath, mechanical per appliance, plus 12% state surcharge (schedule effective July 1, 2025; a July 2026 schedule applies) to your budget. See our detailed Eugene ADU cost guide.
Detached ADUs in Eugene can be up to 800 sq ft or 10% of lot area, whichever is smaller, measured at the exterior walls and including halls, closets, stairs and baths. Attached ADUs are limited to Same cap: 800 sq ft or 10% of lot area, whichever is smaller. Junior ADUs (JADUs) have a cap of N/A (Oregon and Eugene have no junior ADU category; an interior conversion is simply an attached accessory dwelling). Maximum height is Within 60 ft of the front lot line: the zone's main-building height, 30 ft in R-1 (Table 9.2750). More than 60 ft from the front lot line: 25 ft maximum, and from 15 ft above grade the interior setback slopes inward 10 in. per 12 in. of height (EC 9.2751(17)(b)4). For an ADU above a garage or on a lot with 5 ft or more of grade change the slope starts at 22 ft where the lot abuts R-1 land, still capped at 25 ft (EC 9.2751(17)(a)2.b(2)). The 7 ft steep-roof bonus does not apply to ADUs in R-1. You are allowed up to 1 accessory dwelling per lot with a single primary dwelling on a qualifying lot.
Rear setback: 5 ft (Eugene treats side and rear lot lines alike as 'interior yard' setbacks; EC 9.2751(17)(a)2 and (b)4). Eaves and chimneys may project 2 ft into it. On a flag lot the interior setback is 10 ft (EC 9.2775(5)(e)). An ADU above a garage may sit closer with a 10 ft building separation and a recorded maintenance-access easement (EC 9.2751(17)(a)2.c). Side setback: 5 ft interior yard setback (EC 9.2751(17)(a)2 and (b)4; Table 9.2750 alternatively allows 10 ft between buildings). Above 15 ft of height the setback slopes inward toward the 25 ft cap unless the wall is 20 ft or more from the line. Eaves and chimneys may project 2 ft. Front setback: 10 ft (Table 9.2750 R-1 front yard); 18 ft to a garage door or carport post measured along the driveway centerline (Form LU-230). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
None required. The city's ADU page states ADUs do not require additional off-street parking, and ORS 197A.425(1)(b)(B) bars Oregon cities from requiring it (vacation rentals excepted). Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
Not required. The city's ADU page states owner occupancy of either unit is not required; ORS 197A.425 prohibits the condition and Ordinance 20659 (2021) removed it from the Eugene Code. Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Eugene is typically Pre-approved plans: the city says site-specific plan review typically takes 3-4 weeks before the permit can issue (city ADU FAQ). Custom plans go through standard residential plan review; Eugene publishes no target time for it. Plan check: Building plan check is 65% of the building permit fee; waived when you build one of the city's pre-approved plans (only site-related review and fees remain). Pre-approved plans availability: Yes: the Pre-Approved ADU Plans Library has 11 detached plan sets from 287 to 795 sq ft (studio to 2 bedrooms). Ten are sold by their designers for $500 each; the city's own plan, The Joel, is a free download. All are pre-reviewed for building-code compliance, so the plan-review fee is not charged.
Average ADU rental income in Eugene: 1-bedroom units rent for $1,200-$1,500/month, 2-bedroom units for $1,500-$1,900/month. Short-term rentals: Yes. Rentals under 30 days are allowed in a separate dwelling unit; the city requires free annual STR registration and a 4.5% transient room tax. City Council has an open review of STR regulations. Expected ROI: 6-9% gross rental yield (estimate).
The minimum lot size for an ADU in Eugene is None. The city's ADU page states ADUs are not restricted by minimum lot size, lot dimension or maximum density, and EC 9.2751(1)(b) exempts accessory dwellings from Table 9.2750 density limits. Lot coverage still applies: 50% in R-1 (Table 9.2750), and inside Amazon, Fairmount and South University every roofed area counts toward it (EC 9.2751(17)(c)1). This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Eugene, a garage conversion typically costs $60,000-$150,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.
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