An ADU builder in Redmond 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 Redmond'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 Redmond [7]
Based on our Redmond 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) | $255,000-$460,000 |
| Cost per Sq Ft | $310-$510 |
| Garage Conversion | $125,000-$255,000 |
| Prefab / Modular ADU (installed) | $185,000-$355,000 |
| City Permit & Plan Review | Confirm current building permit and plan review amounts with Redmond Development Services at 425-556-2494 — the fee schedule is not part of the zoning code and the city's fee page could not be retrieved for this entry |
| Impact Fees | Capped by state law at 50 percent of the impact fees that would be imposed on the principal unit: "The city or county may not assess impact fees on the construction of accessory dwelling units that are greater than 50 percent of the impact fees that would be imposed on the principal unit" (RCW 36.70A.681(1)(a)). For scale, Redmond's adopted schedules for a single-family residence are $148.78 fire, $6,778.37 park and $5,972.00 school per housing unit, plus a transportation impact fee of $10,022.14 per dwelling unit for Single-Family Detached ($7,604.20 in Centers) or $5,757.40 for Middle Housing ($4,368.37 in Centers) (Redmond Municipal Code 3.10, as amended by Ordinance 3217, approved June 17, 2025). Which land-use category Redmond applies to an ADU is not stated in the schedule — ask Development Services, and cite the 50 percent cap if the quote looks high |
For a full line-item breakdown, see our Redmond ADU cost guide. To confirm what you're allowed to build before you hire, review the Redmond ADU rules (max detached size: 1,000 sq ft. "The total square footage of an ADU shall not exceed 1,000 square feet" (Redmond Zoning Code 21.04.1110.C.3.a), which is exactly the floor RCW 36.70A.681(1)(f) sets — a city may not cap an ADU below 1,000 sq ft, and Redmond has not gone above it. Two discretionary escapes exist: if the ADU occupies an entire single floor of the primary dwelling the Administrator may allow more square footage to use the floor area efficiently, and on a site larger than 10,000 sq ft the Administrator may allow more if the ADU is an affordable housing unit or a public benefit is provided (RZC 21.04.1110.C.3.b-c). Watch the separate accessory-structure cap: the footprint of accessory structures may not exceed 60 percent of the footprint of the ground-floor living area (excluding garage) of the primary dwelling, and in no case may the ADU portion of an accessory structure exceed 1,000 sq ft (RZC 21.04.1120.C.2). On a small house that 60 percent rule bites before the 1,000 sq ft does — if it would push your ADU below 1,000 sq ft, raise RCW 36.70A.681(1)(f) with the planner; owner-occupancy: Not required. RZC 21.04.1110 contains no owner-occupancy provision, no prohibition on renting the owner's unit and no recorded-instrument requirement — all of which the repealed RZC 21.08.220.C.5 used to impose ("Either the primary dwelling unit or the ADU must be occupied by an owner of the property. The owner-occupied unit shall not be rented to others."). Redmond could not reinstate it if it wanted to: RCW 36.70A.681(1)(b) bars a city from requiring the owner of a lot with an ADU to reside in or occupy the ADU or another housing unit on the same lot. The old ban on subdividing or segregating an ADU in ownership (former RZC 21.08.220.C.4) is likewise gone).
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How to Vet an ADU Builder in Redmond
- 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 Redmond 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 (Confirm current building permit and plan review amounts with Redmond Development Services at 425-556-2494 — the fee schedule is not part of the zoning code and the city's fee page could not be retrieved for this entry), plan check (Standard building plan review; no ADU-specific plan check process appears in the zoning code. Where an ADU is created inside an existing structure, expect the Building Official to look at the ceiling-height waiver at RZC 21.04.1110.C.6. Note that Redmond's code does not itself carry the state's conversion protection — RCW 36.70A.681(1)(j) requires a city to allow ADUs converted from existing structures, detached garages included, even where they violate current code requirements for setbacks or lot coverage, while RZC 21.04.1110.C.2.b still says detached ADUs "must each conform to all lot coverage restrictions." If you are converting a garage that does not meet today's setbacks, cite the statute), and impact fees (Capped by state law at 50 percent of the impact fees that would be imposed on the principal unit: "The city or county may not assess impact fees on the construction of accessory dwelling units that are greater than 50 percent of the impact fees that would be imposed on the principal unit" (RCW 36.70A.681(1)(a)). For scale, Redmond's adopted schedules for a single-family residence are $148.78 fire, $6,778.37 park and $5,972.00 school per housing unit, plus a transportation impact fee of $10,022.14 per dwelling unit for Single-Family Detached ($7,604.20 in Centers) or $5,757.40 for Middle Housing ($4,368.37 in Centers) (Redmond Municipal Code 3.10, as amended by Ordinance 3217, approved June 17, 2025). Which land-use category Redmond applies to an ADU is not stated in the schedule — ask Development Services, and cite the 50 percent cap if the quote looks high) are included.
- Permit handling: Confirm they manage Redmond's permit process ("A building permit through Redmond's Development Services / Planning and Building. There is no separate ADU land use permit, no conditional use permit, and — since Ordinance 3220 — no recorded covenant or affidavit: the covenant-recording and cancellation machinery of the repealed RZC 21.08.220.C.5 and C.9 was not carried into RZC 21.04.1110. The portion of the dwelling containing an attached ADU must meet all applicable health and safety codes, except that the Building Official may waive the International Building Code ceiling height requirement where the structure was built in compliance with past building code requirements (RZC 21.04.1110.C.6). State law bars the city from requiring public street improvements as a condition of permitting an ADU (RCW 36.70A.681(1)(l)). Start with Planner on Call at 425-556-2494 or planneroncall@redmond.gov", typically Confirm with Redmond Development Services at 425-556-2494 — no ADU-specific review timeline is published in the zoning code, and the city's own permit pages could not be retrieved for this entry (www.redmond.gov blocks automated access). Redmond adopted Ordinance 3174 in 2024 to conform its permit review procedures to Washington's SB 5290 permit-timeline law, so statutory review clocks apply; ask which category your application falls into) 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 Redmond 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 (Confirm with Redmond Development Services at 425-556-2494 — no ADU-specific review timeline is published in the zoning code, and the city's own permit pages could not be retrieved for this entry (www.redmond.gov blocks automated access). Redmond adopted Ordinance 3174 in 2024 to conform its permit review procedures to Washington's SB 5290 permit-timeline law, so statutory review clocks apply; ask which category your application falls into) 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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