Detached ADU (DADU) Permits in Tacoma
A standalone backyard cottage with its own foundation, roof, and exterior. Maximum flexibility on layout; highest construction cost. State law bars a city maximum below 1,000 sq ft of gross floor area, except on lots with critical areas (RCW 36.70A.681).
Free lookup: your lot’s zoning and setbacks, with a detached ADU placed on it to move and turn.
Permit fees in Tacoma
Set by the Tacoma fee schedule.
Tacoma fee scheduleTacoma's ADU land use permit is $1,330 (Table 4). The building permit is a combination building, mechanical and plumbing permit (Table 8-4): 1.31% of the ICC building valuation for new construction, or 2.81% for an ADU built as an addition, with plan review at 45% of that fee, and a site development permit (grading and erosion control) at 65% of the building permit fee with its own plan review at 45%. Table 1 adds the technology (5%), emergency preparedness (5%) and reserve fund (2%) surcharges, and the natural resources program (5%) on building permits. Apply via aca-prod.accela.com/
Review timeline
Typical: 21–60 business days
Measured, detached ADU: half issued within 138 days of application, 80% within 25575 permits, last 12 months. Source: City of Tacoma residential building permits (Accela Permit Data, City of Tacoma open data).
What Tacoma asks for with a detached ADU
Every application (22)
- New Residential Building permit (BLDRN) application, Accela
- The list's required questions: sizes, height, owner occupancy, parking, rental
- Verification that the Tacoma Water service fee for the new dwelling is paid
- Tacoma Power verification of the electrical line clearances, before submittal
- Site address
- Pierce County parcel number
- Site plan
- Usable yard space calculation, address signage and the walkway to the ADU entry, on the site plan
The other 14
- Utility plan: sewer, water, power, garbage and the impervious surface calculation
- Site Development (SDEV) permit, created with the building permit: the contractor's right-of-way bond
- Foundation plan
- Floor plan
- Roof plan
- Roof + floor framing plan
- Typical building / wall section
- Building elevations N/S/E/W
- Glazing + door schedule (NFRC U-factor / SHGC)
- Structural design notes (loads, materials, inspections)
- Major materials schedule
- Fire-rated wall details, where the ADU is within 5 ft of a property line or 10 ft of the house
- WSEC energy compliance, prescriptive path
- Energy Code Forms: additional credits, insulation, glazing U-values, heating
Where the lot or the work calls for it
Each where the condition beside it holds
- Stormwater Site Plan, "SSP" (more than 2,000 sq ft of new impervious surface, or grading over 50 cu yd)
- Stormwater Pollution Prevention Plan, "SWPPP" (more than 2,000 sq ft of new and replaced impervious surface, or grading over 50 cu yd)
- Structural calculations (vertical and lateral loads), where the plans are engineered
From the city’s own documents: City of Tacoma — Submittal List for: Detached ADU · City of Tacoma — Residential Structure Submittal Checklist, last read October 22, 2026. An address’s own page checks its lot for slopes, flood zones and critical areas.