An ADU builder in Bellevue 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 Bellevue's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in Washington.
What ADU Builders Cost in Bellevue [6]
Based on our Bellevue 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) | $180,000-$380,000 |
| Cost per Sq Ft | $200-$350 |
| Garage Conversion | $90,000-$190,000 |
| Prefab / Modular ADU (installed) | $120,000-$280,000 |
| City Permit & Plan Review | Permit and plan review fees based on project valuation — Confirm with Bellevue Development Services |
| Impact Fees | School/transportation impact fees may apply; HB 1337 caps ADU impact fees at 50% of those for the principal unit — Confirm with Bellevue Development Services |
For a full line-item breakdown, see our Bellevue ADU cost guide. To confirm what you're allowed to build before you hire, review the Bellevue ADU rules (max detached size: 1,200 sq ft (Director may approve more for single-floor units in the primary structure or conversions/additions to existing accessory structures); owner-occupancy: Not required (removed by Ordinance 6746 in 2023; prohibited by HB 1337)).
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How to Vet an ADU Builder in Bellevue
- License: Confirm a current contractor's license in Washington 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 Bellevue 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 (Permit and plan review fees based on project valuation — Confirm with Bellevue Development Services), plan check (Standard plan review; timing varies with queue — Confirm with Bellevue Development Services), and impact fees (School/transportation impact fees may apply; HB 1337 caps ADU impact fees at 50% of those for the principal unit — Confirm with Bellevue Development Services) are included.
- Permit handling: Confirm they manage Bellevue's permit process ("By-right building permit through Development Services (registration and neighbor-notice requirements were removed in 2023)", typically Several weeks to a few months depending on review queue — Confirm with Bellevue Development Services) 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 Bellevue 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 (Several weeks to a few months depending on review queue — Confirm with Bellevue Development Services) 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 Washington ADU client references?
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