An ADU builder in Portland 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 Portland'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 Portland [4][5]
Based on our Portland 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) | $150,000-$300,000 |
| Cost per Sq Ft | $125-$250 |
| Garage Conversion | $70,000-$160,000 |
| Prefab / Modular ADU (installed) | $100,000-$240,000 |
| City Permit & Plan Review | $1,500-$2,500 |
| Impact Fees | Minimal |
For a full line-item breakdown, see our Portland ADU cost guide. To confirm what you're allowed to build before you hire, review the Portland ADU rules (max detached size: 800 sq ft or 75% of primary (whichever is less); owner-occupancy: Not required).
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How to Vet an ADU Builder in Portland
- 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 Portland 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 ($1,500-$2,500), plan check (1-2 weeks), and impact fees (Minimal) are included.
- Permit handling: Confirm they manage Portland's permit process ("By-right approval (no variance needed)", typically 30-45 days) 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 Portland 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 (30-45 days) 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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Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.
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