Everything homeowners ask about building an ADU in Tacoma — answered with 2026 data.
Yes, ADUs are allowed in All residential districts (UR-1, UR-2, UR-3, R-4, R-5) and the mixed-use center (X) districts where dwellings are permitted; TMC 13.06.080.A applies citywide as a subordinate use to any new or existing residential development. In the UR districts a detached ADU is regulated as a 'Backyard Building' housing type (TMC 13.06.100.F.4.b). in Tacoma, WA. The maximum size for a detached ADU is 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). Attached ADUs can be up to 1,000 sq ft of habitable area, excluding garage and non-living areas. Tacoma has an ADU-friendliness score of 8/10. Check our full Tacoma ADU rules page for complete zoning details.
ADU construction in Tacoma typically costs $150,000-$350,000. The cost per square foot averages $300-$520. Garage conversions are more affordable at $75,000-$180,000, while prefab ADUs cost $170,000-$340,000. Permit fees add 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. to your budget. See our detailed Tacoma ADU cost guide.
Detached ADUs in Tacoma can be up to 1,000 sq ft of habitable area, excluding garage and other non-living areas. Attached ADUs are limited to 1,000 sq ft of habitable area, excluding garage and non-living areas. Junior ADUs (JADUs) have a cap of N/A. Washington and Tacoma have no junior ADU category; a small unit inside the house is simply an attached ADU under the same 1,000 sq ft cap. Maximum height is No ADU-specific limit (TMC 13.06.080.A.5.c); the zone and housing-type limits control. UR-1/UR-2: 35 ft, but 25 ft within the rear 25 ft of the lot (35 ft there if a 12-in DBH tree is retained or under the owner-occupant ADU incentive); non-dwelling accessory buildings 15 ft. UR-3: 35 ft. Max 3 stories. In a View Sensitive overlay a backyard building with ADUs may not exceed the main house (TMC 13.06.020.F.1, F.3, F.5). You are allowed up to Two ADUs per lot in any mix: two attached, two detached, or one of each on a qualifying lot.
Rear setback: 15 ft in UR-1/UR-2, 10 ft in UR-3; 0 ft from an alley, and the rear setback may be measured from the alley centerline (TMC 13.06.020.F.1; 13.06.100.F.4.b). Retaining a 12-in DBH tree cuts it to 10 ft (UR-1/2) or 7.5 ft (UR-3). Buildings on the same lot must be 6 ft apart, 10 ft if either is over 25 ft tall. Side setback: 5 ft, or 8 ft on any side of the building where a unit's primary entrance faces that side yard; 0 ft from an alley. A new backyard building behind an existing house may keep 5 ft where existing conditions prevent 8 ft (TMC 13.06.020.F.1). Front setback: 15 ft in UR-1/UR-2, 10 ft in UR-3 (TMC 13.06.020.F.1). A detached ADU is a Backyard Building and sits behind the street-facing structure; on a corner lot it may orient to the secondary street. R-4/R-5 lots use the TMC 13.06.020.G table. Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
None required (TMC 13.06.080.A.4.d; 13.06.090.C Table 1 footnote 17); existing off-street spaces may be removed to site the ADU. Any parking you add must be in the rear portion of the lot, accessed from the alley if one is developable, and never between the building and the street. State floor: RCW 36.70A.681(2). Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
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). Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Tacoma is 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. 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. Pre-approved plans availability: Yes. Four City pre-approved DADU base models: Unit A 300 sq ft studio; Unit B 520 sq ft one-bedroom; Unit C 845 sq ft two-bedroom over a 647 sq ft garage; Unit D stacked duplex of two 534 sq ft one-bedrooms (counts as two ADUs). Each comes in two roof styles with siding options and meets Home In Tacoma standards. The plan sets, site evaluation and staff site visit are free; permit fees and a site-specific review still apply.
Average ADU rental income in Tacoma: 1-bedroom units rent for $1,450-$2,050/month, 2-bedroom units for $1,780-$2,500/month. Short-term rentals: Allowed for the ADU or the main house only if the owner occupies one of the two dwellings (TMC 13.06.080.A.4.g); renting individual guest rooms requires the owner to be home during the stay (TMC 13.06.080.M). Expected ROI: 6-9% gross yield (e.g. $1,700/mo on a $250,000 build is about 8% before vacancy, taxes and the impact fee).
The minimum lot size for an ADU in Tacoma is None. ADUs are permitted on any legally established lot regardless of size or width (TMC 13.06.080.A.5.a). ADUs count toward UR density, but legal lots of record as of Feb 1, 2025 may hold at least 4 dwellings in UR-1, 6 in UR-2 and 8 in UR-3, so a house plus two ADUs fits on any existing lot (TMC 13.06.020.F.1). This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Tacoma, a garage conversion typically costs $75,000-$180,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.
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