An ADU builder in Eugene is a licensed contractor who designs and constructs accessory dwelling units — detached backyard units, garage conversions, attached additions, and junior ADUs (JADUs). Because an ADU is a complete second dwelling, the builder coordinates foundation, framing, plumbing, electrical, and HVAC work and pulls it through Eugene's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in Oregon.
What ADU Builders Cost in Eugene [15]
Based on our Eugene cost data, expect the following ranges from local ADU builders. Quotes for the same scope typically vary 20-40% between contractors, so getting at least three bids is the single best way to control cost.
| New Detached ADU (all-in) | $110,000-$285,000 |
| Cost per Sq Ft | $150-$300 |
| Garage Conversion | $60,000-$150,000 |
| Prefab / Modular ADU (installed) | $90,000-$230,000 |
| City Permit & Plan Review | 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) |
| Impact Fees | System development charges of about $6,000-$10,000 per ADU (city SDC FAQ, Dec 2024; the ADU program page says budget about $7,000) for parks, stormwater and local/regional wastewater; the transportation SDC is reduced 100% for new ADUs. Payable at permit issuance or financed through the city over up to 10 years at prime plus 2%. EWEB charges a separate water SDC. Rates are indexed each July 1 |
For a full line-item breakdown, see our Eugene ADU cost guide. To confirm what you're allowed to build before you hire, review the Eugene ADU rules (max detached size: 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); owner-occupancy: 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).
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How to Vet an ADU Builder in Eugene
- License: Confirm a current contractor's license in Oregon and that it's in good standing. Ask for the license number and verify it with the state board.
- ADU-specific experience: Ask how many ADUs they've completed in or near Eugene and request addresses or photos. ADU permitting and setbacks differ from a kitchen remodel.
- Portfolio & references: Get references from recent ADU clients and, if possible, visit a finished unit.
- Insurance: Verify general liability and workers' compensation coverage. Ask for a certificate of insurance.
- Written, detailed bid: Insist on an itemized, fixed-price or clearly-scoped bid — not a verbal estimate. It should state whether permits (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)), 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)), and impact fees (System development charges of about $6,000-$10,000 per ADU (city SDC FAQ, Dec 2024; the ADU program page says budget about $7,000) for parks, stormwater and local/regional wastewater; the transportation SDC is reduced 100% for new ADUs. Payable at permit issuance or financed through the city over up to 10 years at prime plus 2%. EWEB charges a separate water SDC. Rates are indexed each July 1) are included.
- Permit handling: Confirm they manage Eugene's permit process ("Building permit only, filed through the eBuild portal; zoning compliance is checked in plan review, with no land-use application or neighbor notice. The city recommends meeting Building and Permit Services (541-682-5505) before applying. A pre-approved plan skips building-code plan review; you still submit a site plan for zoning, drainage and SDC review. Converting an existing building that misses a standard needs an adjustment under EC 9.8030(34), unavailable in Amazon, Fairmount or South University", 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) and who is responsible if revisions are required.
- Payment schedule: Avoid large upfront payments. A reasonable schedule ties payments to completed milestones.
Questions to Ask Before You Hire
- How many ADUs have you built in Eugene in the last two years?
- Is your bid fixed-price, and what would trigger a change order?
- Are permits, plan check, and utility connection fees included?
- What's a realistic timeline, including permit review (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) and construction?
- Who is my point of contact and how are delays communicated?
- What warranty do you provide on workmanship?
- Can you share three recent Oregon ADU client references?
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