ADU Costs in Tacoma, Washington

Planning-level pricing guide by ADUWizard.com
Updated for 2026 budgeting

Tacoma is where the Puget Sound ADU math starts to work for more homeowners. You get much of the same demand and rental strength as Seattle, without Seattle’s labor premium and hardest sites. A detached ADU in Tacoma routinely lands well below what the same unit would cost forty minutes north.

This is the Tacoma version of the real budgeting guide, written for a detached ADU, garage conversion, or basement unit in Pierce County in 2026.

Quick disclaimer: A budgeting guide, not a quote or legal advice. Tacoma bids still move with slope, soils, and utility runs, and Washington sales tax (around 10.3%) applies. Use these ranges to compare bids.

Tacoma ADU Cost in 2026 (Quick Answer)

Project scenario	Typical size	Tacoma all-in cost
Garage conversion	400–650 sf	$75k–$180k
Basement / interior ADU	450–800 sf	$130k–$270k
Attached ADU / addition	500–900 sf	$175k–$330k
Detached new-build	500–1,000 sf	$150k–$350k
Prefab / modular installed	500–900 sf	$170k–$340k

A straightforward new detached ADU in the Tacoma area typically runs $150k–$250k for a modest size and finish, with larger or higher-end units pushing toward $350k.

Tacoma ADU Rules That Affect Cost (2026)

Tacoma was an early ADU reformer and now follows Washington’s statewide HB 1337 framework. The specifics that shape your budget:

Rule	Tacoma standard (2026)	Why it matters for cost
Max ADU size	1,000 sf, or 85% of the primary home, whichever is smaller	Smaller homes get a smaller by-right ADU
Max height	No taller than the primary residence	Keeps you to a single story on many lots
Setbacks	5 ft side, 15 ft rear (no setback from alleys), 8 ft if the entrance faces a side line	Alley lots gain usable space
Location	Detached ADU must sit in the rear yard	Shapes where utilities can run
Parking	Not required	Saves paving and drainage cost

What drives cost in Tacoma: utility runs, older-home surprises on conversions, and the usual slope and drainage items. Base labor runs below Seattle, which is most of why totals are lower.

Tacoma ADU Cost by Type and Size (2026)

Type	Typical size	All-in range
Garage conversion	400–650 sf	$75k–$180k
Basement / interior	450–800 sf	$130k–$270k
Attached addition	500–900 sf	$175k–$330k
Detached new-build	500–1,000 sf	$150k–$350k

Size	Conversion	Detached
500 sf	$75k–$180k	$150k–$280k
700 sf	$110k–$240k	$175k–$320k
1,000 sf (Tacoma cap)	$150k–$290k	$210k–$350k

All-in cost per square foot in Tacoma and Pierce County runs roughly $230–$400 for conversions and $300–$520 for detached units.

Example Tacoma Budget: 750 sf Detached ADU (2-Bed)

Category	Budget
Design + engineering	$16,000–$30,000
Permits + fees	$6,000–$16,000
Sitework + utilities	$20,000–$50,000
Foundation + framing + envelope	$70,000–$125,000
MEP	$38,000–$68,000
Interior finishes	$30,000–$60,000
Sales tax + contingency	$22,000–$45,000
Total all-in	$175,000–$330,000

Tacoma ADU Permit Timeline

A realistic total from first inquiry to permit-in-hand is 3–5 months for a straightforward detached unit, with construction adding roughly 4–8 months after that.

FAQs (Tacoma)

How much does an ADU cost in Tacoma in 2026?

Budget roughly $75k–$180k for a garage conversion and $150k–$350k for a detached ADU, depending on size, finish, and site. Tacoma runs meaningfully cheaper than Seattle or the Eastside.

How big can a Tacoma ADU be?

Up to 1,000 sf, or 85% of the primary home’s square footage, whichever is smaller. A detached ADU also cannot be taller than the main house and must sit in the rear yard.

What are the setback rules for a Tacoma ADU?

Generally 5 feet from side lines and 15 feet from the rear, with no setback required from an alley, and 8 feet if the unit’s main entrance faces a side property line. Alley lots effectively gain buildable space.

How much does a garage conversion cost in Tacoma?

Usually $75k–$180k all-in, making it the cheapest ADU path in Tacoma when the existing structure and utilities cooperate.

How long does the Tacoma permit process take?

Plan on about 3–5 months to get a permit in hand for a straightforward detached ADU, then construction on top.

For the statewide view, see our Washington ADU cost guide, compare pricier Seattle ADU costs, and check the Data Hub. City permitting details are at Tacoma Permits.