ADU Builders in Redmond, WA (2026)

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 ^[11]^[12]^[13]^[14]

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)	$325,000-$550,000
Cost per Sq Ft	$400-$650
Garage Conversion	$100,000-$225,000
Prefab / Modular ADU (installed)	$300,000-$450,000
City Permit & Plan Review	Valuation-based (Residential Building Permit Fees, effective Feb. 1, 2025): a $300,000 detached ADU is about $4,069 permit + $2,645 plan review (65%) + $795 planning + $767 fire + 4% technology surcharge, roughly $8,600 before impact and utility fees
Impact Fees	Capped by state law at 50 percent of what the principal unit would pay (RCW 36.70A.681(1)(a)); RMC 3.10 itself carries no ADU line or exemption. For scale, the adopted single-family rates are $148.78 fire, $6,778.37 park and $5,972.00 school (plus a $65 school admin fee) per unit, and a transportation impact fee of $10,022.14 per Single-Family Detached unit ($7,604.20 in Centers) or $5,757.40 for Middle Housing ($4,368.37 in Centers), the category whose ITE basis includes ADUs (RMC 3.10 as amended by Ord. 3217, June 17, 2025; 2025 Impact Fees Schedule). Rates index each January 1 — get the current figure from 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" (RZC 21.04.1110.C.3.a) — exactly the floor RCW 36.70A.681(1)(f) sets. On a site over 10,000 sq ft the Administrator may allow more if the ADU is an affordable unit or a public benefit is provided (C.3.c). Watch the accessory-structure rule: accessory footprints may not exceed 60 percent of the house's ground-floor living area, excluding garage (RZC 21.04.1120.C.2.a); owner-occupancy: Not required. RZC 21.04.1110 (as adopted by Ord. 3220 and amended by Ord. 3261) contains no owner-occupancy clause, no ban on renting the owner's unit and no recorded-covenant requirement; the repealed RZC 21.08.220.C.5 used to impose all three. The city could not reinstate them: RCW 36.70A.681(1)(b) bars requiring the owner of a lot with an ADU to reside in or occupy the ADU or another unit on the lot. Home businesses are allowed in both the ADU and the primary unit (RZC 21.04.1110.C.4)).

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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 (Valuation-based (Residential Building Permit Fees, effective Feb. 1, 2025): a $300,000 detached ADU is about $4,069 permit + $2,645 plan review (65%) + $795 planning + $767 fire + 4% technology surcharge, roughly $8,600 before impact and utility fees), plan check (Standard building plan review at 65 percent of the permit fee, with planning ($794.94 new construction or $312.15 residential addition) and fire ($767.32 new residential construction) review lines; additional reviews after the third are $185 per hour (2025 residential fee table). For an ADU created inside an existing structure the Building Official may waive the IBC ceiling-height requirement where the structure met the code of its day (RZC 21.04.1110.C.5). Redmond's code still says detached ADUs must conform to all lot coverage restrictions (C.2.b), but RCW 36.70A.681(1)(j) requires the city to allow ADUs converted from existing structures, detached garages included, even where they violate current setback or lot coverage rules — cite it if you are converting a garage), and impact fees (Capped by state law at 50 percent of what the principal unit would pay (RCW 36.70A.681(1)(a)); RMC 3.10 itself carries no ADU line or exemption. For scale, the adopted single-family rates are $148.78 fire, $6,778.37 park and $5,972.00 school (plus a $65 school admin fee) per unit, and a transportation impact fee of $10,022.14 per Single-Family Detached unit ($7,604.20 in Centers) or $5,757.40 for Middle Housing ($4,368.37 in Centers), the category whose ITE basis includes ADUs (RMC 3.10 as amended by Ord. 3217, June 17, 2025; 2025 Impact Fees Schedule). Rates index each January 1 — get the current figure from 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 residential building permit through Redmond Development Services — the city's Residential Permits page lists "Adding an Accessory Dwelling Unit (ADU)" alongside new homes and garage conversions. Apply through the Plan Review Online (PRO) request form (no paper plans are accepted; first-time applicants are asked to book an intake appointment); each application gets a Project Coordinator, and the permit is valid for 365 days with each passed inspection extending it 365 days. There is no separate ADU land-use permit, no conditional use permit and, since Ord. 3220, no recorded covenant. Detached ADUs must be fire-sprinklered (city Residential Permits page). Permit Technician: 425-556-2473, permits@redmond.gov", typically Not published for ADUs. State law requires a final decision within 65 days of the completeness determination for permits needing no public notice, with a partial fee refund if missed (RCW 36.70B.080(1)(d), (l)); Redmond's own time frames are in RZC 21.76.040 — ask the Permit Technician) 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 (Not published for ADUs. State law requires a final decision within 65 days of the completeness determination for permits needing no public notice, with a partial fee refund if missed (RCW 36.70B.080(1)(d), (l)); Redmond's own time frames are in RZC 21.76.040 — ask the Permit Technician) 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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Frequently Asked Questions

How much do ADU builders charge in Redmond?

ADU builders in Redmond typically quote $325,000-$550,000 for a new detached unit, or about $400-$650 per square foot, including design, permitting, and construction. A garage conversion runs $100,000-$225,000 and a prefab/modular ADU averages $300,000-$450,000. Add city permit and plan-review fees (Valuation-based (Residential Building Permit Fees, effective Feb. 1, 2025): a $300,000 detached ADU is about $4,069 permit + $2,645 plan review (65%) + $795 planning + $767 fire + 4% technology surcharge, roughly $8,600 before impact and utility fees) plus impact fees of Capped by state law at 50 percent of what the principal unit would pay (RCW 36.70A.681(1)(a)); RMC 3.10 itself carries no ADU line or exemption. For scale, the adopted single-family rates are $148.78 fire, $6,778.37 park and $5,972.00 school (plus a $65 school admin fee) per unit, and a transportation impact fee of $10,022.14 per Single-Family Detached unit ($7,604.20 in Centers) or $5,757.40 for Middle Housing ($4,368.37 in Centers), the category whose ITE basis includes ADUs (RMC 3.10 as amended by Ord. 3217, June 17, 2025; 2025 Impact Fees Schedule). Rates index each January 1 — get the current figure from Development Services and cite the 50 percent cap if the quote looks high. Quotes for the same scope commonly vary 20-40% between builders, so collect at least three bids.

How do I find a good ADU builder in Redmond?

Look for a licensed contractor with completed ADU projects in Redmond specifically — ADUs involve local zoning, setback rules, and utility connections that general remodelers may not have handled. Verify the license, ask for an ADU-specific portfolio and references, confirm they carry liability and workers' comp insurance, and get a written fixed-price or detailed bid. Submit a request below and we'll forward it to local ADU builders serving Redmond for free quotes.

Do ADU builders in Redmond handle permits?

Most full-service ADU builders manage the permit process for you. In Redmond the approval process is "A residential building permit through Redmond Development Services — the city's Residential Permits page lists "Adding an Accessory Dwelling Unit (ADU)" alongside new homes and garage conversions. Apply through the Plan Review Online (PRO) request form (no paper plans are accepted; first-time applicants are asked to book an intake appointment); each application gets a Project Coordinator, and the permit is valid for 365 days with each passed inspection extending it 365 days. There is no separate ADU land-use permit, no conditional use permit and, since Ord. 3220, no recorded covenant. Detached ADUs must be fire-sprinklered (city Residential Permits page). Permit Technician: 425-556-2473, permits@redmond.gov". Review time: not published for ADUs. State law requires a final decision within 65 days of the completeness determination for permits needing no public notice, with a partial fee refund if missed (RCW 36.70B.080(1)(d), (l)); Redmond's own time frames are in RZC 21.76.040 — ask the Permit Technician. Confirm in writing whether permit fees, plan check (Standard building plan review at 65 percent of the permit fee, with planning ($794.94 new construction or $312.15 residential addition) and fire ($767.32 new residential construction) review lines; additional reviews after the third are $185 per hour (2025 residential fee table). For an ADU created inside an existing structure the Building Official may waive the IBC ceiling-height requirement where the structure met the code of its day (RZC 21.04.1110.C.5). Redmond's code still says detached ADUs must conform to all lot coverage restrictions (C.2.b), but RCW 36.70A.681(1)(j) requires the city to allow ADUs converted from existing structures, detached garages included, even where they violate current setback or lot coverage rules — cite it if you are converting a garage), and impact fees are included in the bid or billed separately.

How long does it take to build an ADU in Redmond?

Plan for the permit review (Not published for ADUs. State law requires a final decision within 65 days of the completeness determination for permits needing no public notice, with a partial fee refund if missed (RCW 36.70B.080(1)(d), (l)); Redmond's own time frames are in RZC 21.76.040 — ask the Permit Technician in Redmond) plus construction. Most detached ADUs take 4-8 months of construction after permits are issued; garage conversions and prefab units are often faster. Ask each builder for a realistic schedule and what could delay it.

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What ADU Builders Cost in Redmond [11][12][13][14]