ADU rules in Tacoma

Detached ADUs are a permitted (P) use in all five residential districts (UR-1, UR-2, UR-3, R-4, R-5) and in the commercial and mixed-use center districts. Two ADUs are allowed per residential lot, and TMC 13.06.080A.5.a permits attached and detached ADUs on any legally established lot 'irrespective of lot size or width'. A detached ADU is built as a Backyard Building, one of the five Home in Tacoma housing types, and takes that type's placement standards: zero-foot rear and side setback from an alley, 40 feet maximum width in UR-1 and UR-2 (75 feet in UR-3), 40 feet maximum depth, and 10 feet of separation from other buildings (6 feet where both are under 25 feet tall or an existing tree is retained).

The zoning definition covers a subordinate dwelling 'either within the same building as the main dwelling or in a detached building', so basement conversions, internal splits, and additions all qualify. Either of the two permitted ADUs may be attached or detached; the code sets no required combination. Attached ADUs follow the primary structure's setbacks and the design standards of the housing type they sit inside.

Because the cap measures habitable area only, an attached garage or storage space does not count against the 1,000 sq ft. Home in Tacoma deleted the old sliding cap (the most restrictive of 15 percent of lot area, 85 percent of the primary dwelling's living area, or 1,000 sq ft) that the 2019 tip sheet still describes. Overall bulk is instead governed by the district floor area ratio (0.6 to 1.2 depending on zone and unit count, higher with affordability bonuses) and by the Backyard Building envelope. In a View Sensitive District, a backyard building containing one or two ADUs may be no taller than the primary structure.

TMC 13.06.080A, read in full, imposes no owner-occupancy condition on building or renting an ADU, and the 2019-era requirement that 'both dwellings must be in common ownership' is gone from the current code. Owner occupancy survives in only two places, neither of them a general mandate: short-term rental approval requires the owner to occupy one of the dwellings on the lot, and the voluntary ADU incentive package in TMC 13.06.020F.5 trades development flexibilities (35-foot rear-yard height in UR-1 and UR-2, relaxed alley access, reduced tree credit) for a recorded title restriction keeping one unit owner-occupied for five years. RCW 36.70A.681(1)(b) independently bars Washington cities in this planning group from requiring the owner to live on the lot.

The exemption is citywide and is not conditioned on transit proximity; TMC 13.06.090C footnote 17 repeats it in the off-street parking quantity table. If a homeowner chooses to provide parking for the ADU anyway, it must sit in the rear portion of the lot and may not be accessed from the front where a developable alley exists. The 03/2025 tip sheet still warns that an ADU 'may not remove parking required for the primary dwelling', which the current code text contradicts; the code controls.

ADUs are listed as a permitted (P) use in every residential, commercial, and mixed-use center district use table, with no conditional use permit or discretionary hearing. TMC 13.06.080A.3 requires only a building permit application to Planning and Development Services (application form, floor and structural plans, fees) followed by a City inspection confirming zoning, size, site development, design, and building, health, safety, energy, and electrical standards. Depending on scope the project may also need plumbing, mechanical, site development, side sewer, stormwater, water, or electrical permits, and the city offers pre-approved detached ADU plan sets to shorten review.

The zoning code allows an ADU to be short-term rented subject to TMC 13.06.080A and 13.06.080M, and expressly conditions approval on the owner occupying one of the dwellings, whether the main house or the ADU is the one being rented. The city's short-term rental tip sheet states the corollary: with an ADU on the lot you may short-term rent the ADU or the main dwelling but not both. Chapter 13.06.080M adds safety-sign, smoke and carbon monoxide detector, and occupancy standards. Long-term rental is unrestricted by the zoning code, but the Tax and License Office requires a business license for 'the activity of renting or leasing real property', with every Tacoma rental property registered under it, and the Rental Housing Code (TMC 1.95) applies to the tenancy.