Attached ADU (AADU) Permits in Tacoma
An ADU built inside or attached to the primary residence — basement conversion, garage conversion, or bump-out addition. Lower cost; constrained by the primary footprint.
Free lookup: your lot’s zoning and setbacks, with an attached 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, every ADU type: half issued within 130 days of application, 80% within 24988 permits, last 12 months. Source: City of Tacoma residential building permits (Accela Permit Data, City of Tacoma open data).
What Tacoma asks for with an attached ADU
Every application (13)
- Residential Alteration permit (BLDRA) application, Accela
- The checklist's property information and required questions, signed
- Verification that the Tacoma Water service fee for the new dwelling is paid
- Itemized materials list and labor costs, for the estimated value
- Site address
- Pierce County parcel number
- Site plan
- Usable yard space calculation, address signage, on the site plan
The other 5
- Utility plan: sewer, water, power, garbage and the impervious surface calculation
- Floor plan
- Fire separation details: one-hour separation between the units, or the owner-occupancy agreement with interconnected alarms
- WSEC energy compliance, prescriptive path
- Energy Code Forms: additional credits, insulation, glazing U-values, heating
Where the lot or the work calls for it
Where the work changes the outside walls, windows or roof
- Tacoma Power verification of the electrical line clearances, before submittal (exterior modified)
- Glazing + door schedule (NFRC U-factor / SHGC)
Where the ADU adds onto the house or changes its structure
- Foundation plan
- Roof plan
- Roof + floor framing plan
- Structural design notes (loads, materials, inspections)
Where the ADU adds onto the house or changes its outside walls, windows or roof
- Typical building / wall section
- Building elevations N/S/E/W
- Major materials schedule
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 Checklist for: Attached/Detached ADU Conversion · 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.
AADU-specific requirements
- Egress on every bedroom — IRC R310 net clear opening ≥5.7 sf; sill ≤44″ from floor.
- Smoke + CO alarms — interconnected throughout primary + AADU per IRC R314/R315.
- 1-hr separation — required between AADU and primary in some cases; otherwise a continuous draft stop.
- Independent kitchen + bath — full plumbing + cooking provision in the AADU.
- Address or unit number — the city or county assigns addresses; ask the permit center whether the unit gets its own.