Building an ADU or backyard cottage in Spokane

What you can build in Spokane

Spokane's ADU rules are in Spokane Municipal Code chapter 17C.300. Attached and detached ADUs are permitted in the RA through RHD zones, including planned unit developments. "Two accessory dwelling units are allowed per lot in the RA, R1, R2, RMF, and RHD zones subject to the development standards of the underlying zoning district."

You can create an ADU by:

• Converting existing living area, an attic, a basement or a garage
• Adding floor area to the house
• Building a detached ADU on a lot with a home
• Building a new home with an attached or detached ADU

In the R1, R2, RMF and RHD zones you can also add an ADU on a lot with any principal structure, including non-residential ones. If a new unit could count as either an ADU or a second principal home (such as half of a duplex), you can choose which way to permit it.

The current ADU chapter took effect July 11, 2025 (Ordinance C36696), updating Spokane's code for the state's 2023 ADU law. See our Washington ADU law page for the state rules. [1]

Size, height and setbacks

Size. An attached ADU "must be not more than one thousand (1,000) square feet, excluding any related garage area." Before you add one, the house must have at least 1,000 square feet of floor area, not counting an attached garage. Converting an existing basement or attic can exceed the 1,000 square foot limit. A detached ADU "shall not exceed one thousand (1,000) square feet of floor area."

Detached ADU standards (all residential zones):

• Maximum building footprint: 1,200 square feet
• Maximum height: 25 feet
• Rear setback: 5 feet, or 0 feet with an alley
• Side setbacks: the same as for the house, which from an interior side lot line is 3 feet on lots 40 feet wide or less and 5 feet on wider lots (5 feet from a street side lot line), plus an angled setback from interior side lot lines

Setbacks for a detached accessory structure can be reduced to zero with a signed waiver from your neighbor, under SMC 17C.111.240. Attached ADUs count toward the house's maximum building footprint. Building coverage limits for the whole lot are 50 percent in RA, 65 percent in R1 and 80 percent in R2. All of these numbers are in Table 17C.111.205-2. [1][2]

Parking

ADU parking rules follow chapter 17C.230, and its rule is simple: "there is no required minimum number of off-street parking spaces," except as a condition of a conditional use permit. That rule took effect March 6, 2025. [1][3]

Fees

Spokane's 2026 development fee schedule sets plan review for new single-family homes, ADUs and duplexes at 50 percent of the job value fee. The job value fee is based on your project's valuation; for example, a project valued at $100,001 to $500,000 pays a $972 base fee plus $5 for each $1,000 over $100,000. The ADU application form says plan review, processing and state building code fees are due when you apply.

Spokane also collects transportation impact fees under SMC chapter 17D.075, whose fee schedule was last updated effective March 19, 2026. Washington law says a city may not charge impact fees on an ADU "greater than 50 percent" of the fees for the main house. Ask the Permit Center what your ADU will owe.

An ADU "must utilize those municipal utilities and address established for the principal dwelling unit." For budgeting help, see our ADU cost guide. [1][4][5][6][7]

Garage and other conversions

Converting a garage, attic, basement or existing living area is one of the listed ways to create an ADU. You can convert an existing detached accessory structure even if it sits in the front setback. Conversions of structures in a side or rear setback are allowed as provided in the city's setback and accessory structure rules (SMC 17C.111.235 and 17C.111.240).

If you add floor area to an existing detached structure to fit the ADU, the whole structure must meet the zone's development standards. Any conversion must meet building, electrical, fire and plumbing codes. See our garage conversion guide for the general steps. [1]

Renting it out

You can rent an ADU long term without living on the property. Washington law bars cities from requiring the owner to live in the ADU or the main house.

Short-term rentals (fewer than 30 consecutive days) need a city permit. Where a lot with an ADU also has a short-term rental, an owner must live in one of the units as a permanent residence for more than six months a year and can't receive rent for that unit. The code allows one short-term rental in a house or an ADU, or one in each, subject to that owner-occupancy rule. If the owner stops living there, the ADU approval expires. Short-term rentals must also meet state insurance and safety rules in chapter 64.37 RCW. [1][7][8]

More homes on one lot

Spokane's residential zones have no maximum density on sites of 2 acres or less, and the R1 and R2 zones allow new lots as small as 1,200 square feet. Unit lot subdivisions have no minimum child lot area. If a new unit meets the rules for both an ADU and a second principal home, such as the second unit of a duplex, you can choose how to permit it. Ask the Development Services Center which approach fits your lot. [1][2]

Older city handouts may be out of date

The city's "Accessory Dwelling Unit Current Allowances" handout, updated August 2022, still lists an 800 square foot limit for attached ADUs and parking for ADUs with two or more bedrooms. The 2025 code replaced those rules with a 1,000 square foot limit and no parking minimum. Where they differ, rely on the current code and confirm with the Development Services Center. [1][3][9]

Permit steps in Spokane

1. Confirm you're in the city and check your zone

   Spokane addresses aren't always inside city limits. Use Spokane County's SCOUT property dashboard, linked from the city's residential permit process page, and check your zone in SMC 17C.111.205. [2][10]

2. Talk to the Permit Center

   Call 509-625-6300 or email PermitTeam@spokanecity.org with questions about your lot before you draw plans. [10]

3. Prepare plans and the application

   Fill out the ADU building permit application with a site plan. A new ADU needs Washington State Energy Code worksheets before plans can be reviewed. [5]

4. Submit and pay intake fees

   Submit at the Development Services Center, 3rd floor of City Hall, or through online permitting if you're a registered licensed contractor. Plan review, processing and state building code fees are due at submittal. [5][10][11]

5. Get your permit

   After plan review, pay the remaining permit fees and any transportation impact fees, and get your building permit. [1][4][6]

6. Schedule inspections

   Call the inspector listed on your permit before 8:30 a.m. on the day you want an inspection and leave a message with your permit number and address. You must request a final inspection. [12]

7. Get a certificate of occupancy

   An ADU needs both a building permit and a certificate of occupancy before anyone can live in it. [1]

Who to call

• Development Services Center & Permit Center

  ADU permits, zoning questions, plan review and fees

  509.625.6300

  3rd Floor City Hall, 808 W Spokane Falls Blvd, Spokane, WA 99201

  [10]

• City of Spokane Inspections

  Building, plumbing, electrical and mechanical inspections

  509.625.6300

  [12]

Questions people ask