An ADU builder in Tacoma 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 Tacoma'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 Tacoma [15][16][17]
Based on our Tacoma 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-$350,000 |
| Cost per Sq Ft | $300-$520 |
| Garage Conversion | $75,000-$180,000 |
| Prefab / Modular ADU (installed) | $170,000-$340,000 |
| City Permit & Plan Review | PDS Fee Estimator (2026): building and site permit plus plan review about $2,000 for a 300 sq ft studio, $3,500 for 520 sq ft and $6,600 for 1,000 sq ft (valuation $170.80/sq ft x 1.31%, plus 45% plan review, site development and 17% surcharges). Electrical, water and sewer fees are separate. |
| Impact Fees | Transportation impact fee since June 1, 2026 (TMC 10.31, Ord. 29082): an ADU pays 50% of the single-family rate for its district; per-trip rates run $741 (Northeast Tacoma) to $5,201 (Southeast Tacoma) plus 3% admin, due before the permit issues, deferrable to final inspection. No school or park impact fees. TPU connection charges: power $970-$1,797; water $176 on the house meter, $5,922-$10,272 for a separate service. |
For a full line-item breakdown, see our Tacoma ADU cost guide. To confirm what you're allowed to build before you hire, review the Tacoma ADU rules (max detached size: 1,000 sq ft of habitable area, excluding garage and other non-living areas (TMC 13.06.080.A.5.b). A Backyard Building is also limited to 40 ft wide (75 ft in UR-3) and 40 ft deep, and the lot's total floor area must stay within the UR FAR cap (UR-1: 0.6 for 1-2 units, 0.8 for 3+; UR-2: 0.8/1.0; UR-3: 1.0/1.2; TMC 13.06.020.F.1).; owner-occupancy: Not required to build or rent an ADU long-term (RCW 36.70A.681(1)(b); no requirement in TMC 13.06.080.A). One exception: to use the ADU or the main house as a short-term rental, the owner must occupy one of the dwellings (TMC 13.06.080.A.4.g).).
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How to Vet an ADU Builder in Tacoma
- 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 Tacoma 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 (PDS Fee Estimator (2026): building and site permit plus plan review about $2,000 for a 300 sq ft studio, $3,500 for 520 sq ft and $6,600 for 1,000 sq ft (valuation $170.80/sq ft x 1.31%, plus 45% plan review, site development and 17% surcharges). Electrical, water and sewer fees are separate.), plan check (Plans must show a site plan, floor plans, elevations, structural details, WSEC energy credits and fire separation; the ADU needs a separate visible address, its own heating and water-heater control, cooking, sanitation and sleeping facilities, and interconnected smoke/CO alarms if attached. Use the PDS Submittal Checklist for a Detached or Attached ADU.), and impact fees (Transportation impact fee since June 1, 2026 (TMC 10.31, Ord. 29082): an ADU pays 50% of the single-family rate for its district; per-trip rates run $741 (Northeast Tacoma) to $5,201 (Southeast Tacoma) plus 3% admin, due before the permit issues, deferrable to final inspection. No school or park impact fees. TPU connection charges: power $970-$1,797; water $176 on the house meter, $5,922-$10,272 for a separate service.) are included.
- Permit handling: Confirm they manage Tacoma's permit process ("Residential new-construction building permit from Planning and Development Services, applied for online through the Accela portal at tacomapermits.org. The combined permit covers building, plumbing, mechanical and site development; electrical is a separate permit from Tacoma Power, and side-sewer, water and stormwater permits are added as the scope requires. Optional DADU coaching: file a PRE request for staff feedback on land use, building and site development, with a site visit, before you apply (TMC 13.06.080.A.3; PDS ADU pages).", typically PDS publishes no fixed ADU review target; its Permit Timeline page reports actual first-review and issuance times for buildings of up to six units (Oct 2025-Mar 2026 snapshot). A 2026 industry guide budgets 3-5 months of review; pre-approved plans are quicker but still get a site-specific review.) 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 Tacoma 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 (PDS publishes no fixed ADU review target; its Permit Timeline page reports actual first-review and issuance times for buildings of up to six units (Oct 2025-Mar 2026 snapshot). A 2026 industry guide budgets 3-5 months of review; pre-approved plans are quicker but still get a site-specific review.) 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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