Everything homeowners need to know about building an accessory dwelling unit in Spokane - size limits, setbacks, permits, and how the city's own standards layer on top of Washington's statewide ADU law.
Last verified: August 2026
7/10 · ADU-friendly
1,000 sq ft
Max ADU size
24 ft*
Max height
Not required*
Owner-occupancy
By-right
Permit type
This page summarizes Spokane Municipal Code Chapter 17C.300 (Accessory Dwelling Units), as amended for compliance with Washington's statewide ADU law (HB 1337, 2023), for general reference - it is not legal advice. Always confirm current requirements with Spokane Planning & Development Services before designing or applying for permits. See sources below.
Zoning & size requirements
What you're allowed to build
ADU type
Max size
Max height
Notes
Detached
1,000 sq ft of floor area, raised from a previous 975 sq ft cap under the city's 2025 HB 1337 compliance update
Set zone-by-zone in the city's ADU development-standards table (SMC 17C.111.205-2)
Combined coverage of all detached accessory structures is capped at 15% of lot area on lots 5,500 sq ft or larger, 20% on smaller lots
Internal / attached ADU
1,000 sq ft, raised from a previous 800 sq ft cap; the principal structure must be at least 800 sq ft before an internal ADU can be established
Same as primary structure
Common approach for basement, attic, or garage conversions; up to 2 bedrooms allowed
Allowed zoning districts
Attached and detached ADUs are permitted citywide in the RA through RHD residential zones (including planned unit developments), with up to 2 ADUs per lot allowed in the RA, R1, R2, RMF, and RHD zones. Detached ADU setbacks and height are set zone-by-zone in the city's development-standards table; Washington's statewide floor under HB 1337 requires cities to allow ADU heights up to at least 24 ft where the primary home is that tall. Confirm your parcel's exact figures with Planning & Development Services.
Additional standards
Setbacks, parking & other rules
Setbacks
Set zone-by-zone in SMC 17C.111.205-2; conversions of existing accessory structures in a side or rear setback are generally allowed, but not in a front setback
Parking
Studio and 1-bedroom ADUs require no additional off-street parking; parking is not required for residential development within a half-mile of a transit stop
Units per lot
Up to 2 ADUs (any mix of attached and detached) per lot in the RA, R1, R2, RMF, and RHD zones, raised from 1 under the city's 2025 HB 1337 compliance update
Owner-occupancy
Not required for a standard long-term-rental ADU. If the same lot also has a permitted Short-Term Rental, one of the dwelling units must be owner-occupied as the owner's permanent residence for more than 6 months a year
Building code
Must meet Washington State Residential Code dwelling-unit standards; the ADU must use the same municipal utilities and address as the primary dwelling
Impact fees
Capped at no more than 50% of what's charged for the primary dwelling unit, per HB 1337
Ordinance history
How Spokane's ADU rules got here
2021Fee waiver for centers and corridors. On November 15, 2021, the City Council unanimously waived ADU permit fees for homeowners near designated centers and corridors like Garland Avenue and South Perry, saving roughly $5,100 in fees on a unit valued between $50,000 and $100,000. At the time, owner-occupancy was still required citywide, and the waiver was set to expire at the end of 2024 pending renewal.
2022Local code loosened. Spokane amended its housing code to increase allowable ADU size, remove design-matching requirements like matching windows and roofline, and eliminate the general owner-occupancy requirement. Permitting roughly doubled afterward, from the teens to about 29-30 ADUs per year in 2023 and 2024.
2023Washington passes HB 1337. The statewide law requires cities to allow 2 ADUs per lot in urban growth areas, guarantees at least 1,000 sq ft of ADU floor area, caps ADU impact fees at 50% of the primary unit's fee, and bars parking mandates near transit.
2025Local code brought into compliance. Spokane amended Chapter 17C.300 SMC to move from 1 to 2 ADUs per lot, raise the detached ADU cap from 975 to 1,000 sq ft (and the internal ADU cap from 800 to 1,000 sq ft), and limit the standing owner-occupancy requirement to lots that pair an ADU with a Short-Term Rental, effective by the state's June 30, 2025 compliance deadline.
Spokane is Washington's second-largest city by some counts and its third-largest metro area after Seattle and Tacoma, with a housing market that generally runs more affordable than the state's west-side cities. Local builders have reported growing demand since the 2022 reform; one Spokane-based ADU company reported completing 6 units in 2024 and expected to start more than 20 in 2025.
Permit process
How Spokane ADU permitting works
1
Pre-application check
Confirm your zone and applicable development-standards table with Spokane Planning & Development Services before you design.
2
Prepare your plan set
You'll need a site plan and floor plans; for an internal ADU, floor plans confirming the principal structure meets the 800 sq ft minimum before conversion.
3
Submit your application
Apply for a building permit and certificate of occupancy through the city's Business & Development Services Center.
4
Plan review
Review generally takes several weeks depending on scope and current volume; ask whether any fee-reduction or fee-waiver program is currently active for your area.
5
Building permit & inspections
Once approved, pull your building permit, begin construction, and schedule the standard framing, plumbing, electrical, and final inspections.
Fees and timelines change as the city updates its schedule - confirm current figures with Planning & Development Services before budgeting.
Budgeting
What it costs to build an ADU in Spokane
Garage conversion
Roughly $65,000-$150,000, toward the lower end of the regional range given Spokane's generally more affordable construction market
New detached ADU
Roughly $140,000-$280,000+ for a code-compliant, freestanding unit
Permit fees
The city has previously offered temporary fee waivers or reductions for qualifying ADU projects near designated centers and corridors - confirm current availability with Planning & Development Services
These are general ranges from local contractor estimates and regional reporting, not quotes - actual cost depends heavily on lot conditions, finishes, and whether utilities need to be extended. Spokane's construction market generally runs more affordable than Seattle or Tacoma, though costs still vary by contractor and project scope.
Before you apply
Tips for a smooth approval
Ask about active fee-waiver or fee-reduction programs. Spokane has offered temporary ADU permit fee waivers tied to specific neighborhoods before - confirm what's currently available before you budget.
Plan for two ADUs if you might want them. Spokane now allows up to two ADUs per lot in most residential zones, so decide early whether you want one attached and one detached.
Confirm your exact zone's height and setback figures. These are set zone-by-zone in the city's development-standards table rather than as a single citywide number, so verify before finalizing your design.
Understand the short-term-rental owner-occupancy rule. Standard long-term ADUs have no owner-occupancy requirement, but pairing an ADU with a short-term rental on the same lot brings one back.
Check whether your lot qualifies for reduced or eliminated parking. Studio and 1-bedroom ADUs need no additional parking, and transit-adjacent lots get a further exemption under state law.
FAQ
Common questions
Do I need to live on the property to build an ADU in Spokane?
No, not for a standard long-term-rental ADU - the city removed its general owner-occupancy requirement in 2022, consistent with Washington's statewide HB 1337. If the same lot also has a permitted Short-Term Rental, one of the dwelling units must be owner-occupied.
How many ADUs can I build on one lot in Spokane?
Up to 2, in any combination of attached and detached, in the RA, R1, R2, RMF, and RHD zones - raised from 1 under the city's 2025 HB 1337 compliance update.
Do I need extra parking for an ADU?
Studio and 1-bedroom ADUs require no additional off-street parking, and parking is not required at all for residential development within a half-mile of a transit stop.
What's the maximum size for an ADU in Spokane?
1,000 sq ft of floor area for both detached and internal ADUs, raised in 2025 from previous caps of 975 sq ft (detached) and 800 sq ft (internal).
How long does the permit process take?
Review generally takes several weeks depending on project scope and current volume - confirm current timelines with Planning & Development Services.
How much does an ADU cost to build in Spokane?
Garage conversions tend to run roughly $65,000-$150,000, and new detached units roughly $140,000-$280,000 or more, based on local contractor estimates and regional reporting. Spokane generally runs more affordable than Seattle or Tacoma.
Has Spokane's 2022 reform actually increased ADU construction?
Yes. Permitting roughly doubled after the 2022 code changes, moving from permits "in the teens" to about 29-30 per year in 2023 and 2024, and local builders report continued growth in demand since.
Are ADU permit fee waivers still available in Spokane?
The city has offered temporary fee waivers for ADU projects near designated centers and corridors in the past, with at least one waiver program originally set to expire at the end of 2024 pending council renewal. Confirm current availability directly with Planning & Development Services before budgeting.
