ADU Costs in Spokane, Washington

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

Spokane is the number I point people to when they assume every Washington ADU costs Seattle money. It does not. Eastern Washington labor is cheaper, the sites are generally flatter and easier, and the permit path is fast and inexpensive. Spokane is where a small detached ADU can actually pencil out for a normal homeowner.

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

Quick disclaimer: A budgeting guide, not a quote or legal advice. Even in Spokane, utility runs and older-home surprises move budgets, and Washington sales tax (around 9% here) still applies. Use these ranges to compare bids.

Spokane ADU Cost in 2026 (Quick Answer)

Project scenario	Typical size	Spokane all-in cost
Garage conversion	400–650 sf	$50k–$120k
Basement / interior ADU	450–800 sf	$95k–$210k
Attached ADU / addition	500–900 sf	$130k–$260k
Detached new-build	500–1,000 sf	$110k–$260k
Prefab / modular installed	500–900 sf	$135k–$280k

Overall, Spokane ADU construction typically runs $110k–$220k, with garage conversions the cheapest path at roughly $50k–$120k.

Spokane ADU Rules That Affect Cost (2026)

Spokane follows Washington’s statewide HB 1337 framework, and its local process is refreshingly light and cheap.

Rule	Spokane standard (2026)	Why it matters for cost
ADUs per lot	Up to two in residential zones	Room to add over time
Max detached size	Up to about 1,000 sf	A real 1–2 bedroom unit is by-right
Max height	Generally about 20 ft	Keeps most units single-story
Setbacks	Roughly 15 ft rear as a common reference, varies by zone	Confirm your zone before you design
Parking	None for studios and 1-beds; a 2-bed may need one space	Saves paving on smaller units
Owner-occupancy	Not required	Removes a financing and resale drag
Permit fees / review	Commonly $2,000–$3,500, review around 50–75 days	Among the cheapest, fastest in the state

What drives cost in Spokane: mostly utilities and older-home conversion surprises. Slope and soils matter less here than around Puget Sound, which keeps sitework budgets down.

Spokane ADU Cost by Type and Size (2026)

Type	Typical size	All-in range
Garage conversion	400–650 sf	$50k–$120k
Basement / interior	450–800 sf	$95k–$210k
Attached addition	500–900 sf	$130k–$260k
Detached new-build	500–1,000 sf	$110k–$260k

Size	Conversion	Detached
500 sf	$50k–$120k	$110k–$200k
700 sf	$85k–$180k	$135k–$235k
1,000 sf	$120k–$210k	$170k–$260k

All-in cost per square foot in Spokane and Eastern Washington runs roughly $190–$340 for conversions and $260–$450 for detached units.

Example Spokane Budget: 600 sf Detached ADU (1-Bed)

Category	Budget
Design + engineering	$10,000–$20,000
Permits + fees	$2,000–$3,500
Sitework + utilities	$12,000–$35,000
Foundation + framing + envelope	$55,000–$100,000
MEP	$28,000–$50,000
Interior finishes	$22,000–$45,000
Sales tax + contingency	$16,000–$32,000
Total all-in	$130,000–$240,000

Spokane ADU Permit Timeline

Spokane’s permit review commonly runs 50–75 days, one of the faster and cheaper processes in the state, with fees often in the $2,000–$3,500 range. Add design time before and construction after, and a straightforward project can finish in well under a year.

FAQs (Spokane)

How much does an ADU cost in Spokane in 2026?

Budget roughly $50k–$120k for a garage conversion and $110k–$260k for a detached ADU. Spokane is the most affordable major ADU market in Washington by a wide margin.

Why is Spokane so much cheaper than Seattle?

Lower labor costs, easier and flatter sites, a lighter and cheaper permit process, and a lower sales-tax rate (around 9% versus 10.25% in Seattle). The gap on a detached unit can be well over $200k.

How big can a Spokane ADU be?

Detached ADUs are generally allowed up to about 1,000 sf, with a height limit near 20 feet. Confirm your zone’s specific setback and size details before you design.

Do I need parking for a Spokane ADU?

Studios and one-bedroom ADUs generally require no additional parking; a two-bedroom unit may need one space. This keeps sitework low on smaller units.

How fast and cheap is the Spokane permit process?

Review commonly runs 50–75 days, with fees often in the $2,000–$3,500 range, among the quickest and cheapest in Washington.

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 the City of Spokane.