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ADU Rules in Spokane, Washington

Complete guide to building an Accessory Dwelling Unit in Spokane — zoning, setbacks, permits, costs, and more.

Max Size: 1,000 sq ft of floor area (SMC 17C.300.110(A)(2)). Building footprint up to 1,200 sq ft in every residential zone (Table 17C.111.205-2), counted within the lot's total building coverage cap of 50% in RA, 65% in R1, 80% in R2 and 100% in RMF/RHD (Table 17C.111.205-1, note 5). Setbacks: 0 ft where the rear lot line abuts an alley; 5 ft where there is no alley (Table 17C.111.205-2). An existing garage or shed already inside a rear or side setback may be converted in place (SMC 17C.300.130(B)(4), 17C.111.240), but any added floor area puts the whole structure under current setbacks. Parking: Varies Verified: 2026-09-20

Researched by ADU Zoning Hub · verified 2026-09-20 against Spokane planning code and Washington ADU law · methodology · 21 sources cited ↓

ADU Score: 8/10
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Are ADUs allowed in Spokane, WA? [1][2][3][4][5][6][7][8]

Yes. Spokane allows ADUs on most residential lots. A detached unit can be up to 1,000 sq ft, set 0 ft back from the rear line. Parking varies by lot and unit size. Owner-occupancy is not required, so the unit can be rented out. A building permit is required and applications are reviewed through the standard permit process.

Maximum size1,000 sq ft of floor area (SMC 17C.300.110(A)(2)). Building footprint up to 1,200 sq ft in every residential zone (Table 17C.111.205-2), counted within the lot's total building coverage cap of 50% in RA, 65% in R1, 80% in R2 and 100% in RMF/RHD (Table 17C.111.205-1, note 5).
SetbacksRear 0 ft where the rear lot line abuts an alley; 5 ft where there is no alley (Table 17C.111.205-2). An existing garage or shed already inside a rear or side setback may be converted in place (SMC 17C.300.130(B)(4), 17C.111.240), but any added floor area puts the whole structure under current setbacks. · Side Same as the primary structure: 3 ft from an interior side lot line on lots 40 ft wide or less, 5 ft on wider lots, and 5 ft from a street side lot line (Table 17C.111.205-2). An additional angled setback applies near the interior side line (SMC 17C.111.230(C), 17C.111.235(E)); a detached structure's setback may drop to 0 ft with a signed neighbor waiver (SMC 17C.111.240(C)).
ParkingNone. Spokane removed all minimum off-street parking requirements citywide (SMC 17C.230.110, Ordinance C36629, effective March 6, 2025), and SMC 17C.300.130(A)(3) simply refers ADUs to Chapter 17C.230. State law would in any case bar parking mandates within 1/2 mile of a major transit stop (RCW 36.70A.681(2)).
Owner-occupancyNot required. The only exception: if the lot also has a short-term rental under Chapter 17C.316 SMC, one unit must be the owner's principal residence for more than six months a year and cannot be rented (SMC 17C.300.110(B)); the ADU approval is then transferable only to a buyer who will owner-occupy (SMC 17C.300.140).

Do I need a permit to build an ADU in Spokane? [9][10][11][12][13][14][15]

Yes. Every ADU in Spokane needs a building permit. Review process: Building permit plus a certificate of occupancy from the Development Services Center, 3rd floor City Hall (SMC 17C.300.120); no land-use hearing or design review. Mechanical, electrical and plumbing permits are separate. The ADU uses the principal dwelling's utilities and street address (SMC 17C.300.130(C))..

Permit feesAbout $2,000-$3,200 in city fees for a $150,000-$300,000 ADU (2025 New SFR/ADU fee table: $65 processing, plan review at 50% of the permit fee, $100 stormwater review, 2.5% technology fee, $6.50 state fee). A CPI-adjusted 2026 schedule now applies; confirm with the DSC.
Typical timelineThe city publishes no ADU-specific review time. State law (RCW 36.70B.080(1)(d)) makes 65 days from a complete application the default for permits that need no public notice, unless Spokane has adopted its own periods; ask the Development Services Center (509-625-6300).
Official Spokane links:

Three things to know before you build in Spokane

  • Alley lots are the sweet spot: a detached ADU may sit on the rear lot line where it abuts an alley (Table 17C.111.205-2), and Spokane requires no parking, so the rear yard is fully usable up to the 1,200 sq ft footprint and the zone's building coverage cap
  • Converting a garage or shed: SMC 17C.300.130(B)(4) lets a structure already inside a rear or side setback become an ADU without being moved, but adding floor area brings the whole building under current setbacks and height (25 ft)
  • Attached ADU threshold: the house must already have 1,000 sq ft of floor area (garage excluded) before you carve out an attached unit; a basement or attic conversion is exempt from the 1,000 sq ft ADU cap (SMC 17C.300.110(A)(1))

Last verified 2026-09-20 against Spokane planning code. How we verify

Spokane allows two accessory dwelling units on any lot in its RA, R1, R2, RMF and RHD residential zones, attached or detached, with a building permit and no public hearing (SMC 17C.300.100, Ordinance C36696, effective July 11, 2025). Each ADU may have up to 1,000 sq ft of floor area; a detached unit may cover up to 1,200 sq ft of footprint, rise 25 ft, and sit on the rear lot line where the lot backs onto an alley (5 ft otherwise) (SMC 17C.300.110 and Table 17C.111.205-2). Owner-occupancy is not required unless the lot also holds a short-term rental, and no off-street parking is required anywhere in the city (SMC 17C.230.110). The 2025 fee table puts city permit fees at about $2,000-$3,200 for a $150,000-$300,000 project; transportation impact fees are extra and capped by state law at half the single-family rate.

In Spokane you will also hear an ADU called a DADU — short for detached accessory dwelling unit, the usual term across Washington. The rules on this page apply either way.

Zoning & Size Requirements [1][2][3][4][5][6][7][8]

Yes — Spokane allows ADUs. A detached ADU can typically be up to 1,000 sq ft under current Washington and Spokane zoning rules.

See what this means for your lot — ask Spokane ADU builders for a quote →

Allowed ZonesAll residential zones, RA, R1, R2, RMF and RHD, including planned unit developments; attached or detached (SMC 17C.300.100(A)). In R1, R2, RMF and RHD an ADU may also be added to a lot whose principal structure is non-residential (SMC 17C.300.130(A)(1)(f)).
Max Size (Detached)1,000 sq ft of floor area (SMC 17C.300.110(A)(2)). Building footprint up to 1,200 sq ft in every residential zone (Table 17C.111.205-2), counted within the lot's total building coverage cap of 50% in RA, 65% in R1, 80% in R2 and 100% in RMF/RHD (Table 17C.111.205-1, note 5).
Max Size (Attached)1,000 sq ft, excluding any related garage area (SMC 17C.300.110(A)(1)). The house must already have at least 1,000 sq ft of floor area (attached garage excluded) before an attached ADU is created; a converted basement or attic may exceed the 1,000 sq ft cap. An attached ADU counts toward the primary building's footprint limit (2,450 sq ft on R1/R2 lots of 7,000 sq ft or less, 35% of larger lots).
Max Size (JADU)Not a category in Spokane or Washington law. A basement or attic converted inside the house is simply an attached ADU, and that conversion may exceed the 1,000 sq ft cap (SMC 17C.300.110(A)(1)(c)).
Max Height25 ft for a detached ADU in every residential zone (Table 17C.111.205-2, accessory dwelling units rows); the state floor is 24 ft (RCW 36.70A.681(1)(g)). Primary buildings may reach 35 ft in RA and 40 ft in R1 through RHD.
Max UnitsTwo ADUs per lot in the RA, R1, R2, RMF and RHD zones, in any mix of attached and detached (SMC 17C.300.100(B)). Where a unit could qualify as either an ADU or a second principal dwelling (for example a second house on the lot), the applicant chooses which set of standards to permit it under (SMC 17C.300.100(C)).

Setback Requirements [1][2][3][4][5][6][7][8]

Spokane allows a 0 ft rear setback for a detached ADU in some cases (the setbacks row gives the conditions), and parking requirements vary by unit size or location. Owner-occupancy is not required — you can rent it out without living on the property.

Rear Setback0 ft where the rear lot line abuts an alley; 5 ft where there is no alley (Table 17C.111.205-2). An existing garage or shed already inside a rear or side setback may be converted in place (SMC 17C.300.130(B)(4), 17C.111.240), but any added floor area puts the whole structure under current setbacks.
Side SetbackSame as the primary structure: 3 ft from an interior side lot line on lots 40 ft wide or less, 5 ft on wider lots, and 5 ft from a street side lot line (Table 17C.111.205-2). An additional angled setback applies near the interior side line (SMC 17C.111.230(C), 17C.111.235(E)); a detached structure's setback may drop to 0 ft with a signed neighbor waiver (SMC 17C.111.240(C)).
Front SetbackNot listed separately for ADUs in Table 17C.111.205-2. The primary-building front setback is 10 ft in R1, R2, RMF and RHD and 15 ft in RA, and state law bars an ADU setback stricter than the principal unit's (RCW 36.70A.681(1)(h)). SMC 17C.300.130(B)(4)(a) addresses converting an existing detached structure that sits in the front setback; confirm placement with the Planning Services Department.
Parking RequiredNone. Spokane removed all minimum off-street parking requirements citywide (SMC 17C.230.110, Ordinance C36629, effective March 6, 2025), and SMC 17C.300.130(A)(3) simply refers ADUs to Chapter 17C.230. State law would in any case bar parking mandates within 1/2 mile of a major transit stop (RCW 36.70A.681(2)).
Owner OccupancyNot required. The only exception: if the lot also has a short-term rental under Chapter 17C.316 SMC, one unit must be the owner's principal residence for more than six months a year and cannot be rented (SMC 17C.300.110(B)); the ADU approval is then transferable only to a buyer who will owner-occupy (SMC 17C.300.140).
Min Lot SizeNone for an ADU: Chapter 17C.300 sets no minimum lot area, so any existing residential lot qualifies (state floor: RCW 36.70A.681(1)(e)). For new subdivisions the minimum lot is 1,200 sq ft in R1 through RHD and 7,200 sq ft in RA (Table 17C.111.205-1). The only size test is for attached ADUs: the house must be at least 1,000 sq ft.

Permit Process & Fees [9][10][11][12][13][14][15]

An ADU permit in Spokane goes through a standard permit review. The city publishes no ADU-specific review time. State law (RCW 36.70B.080(1)(d)) makes 65 days from a complete application the default for permits that need no public notice, unless Spokane has adopted its own periods; ask the Development Services Center (509-625-6300). Permit fees: About $2,000-$3,200 in city fees for a $150,000-$300,000 ADU (2025 New SFR/ADU fee table: $65 processing, plan review at 50% of the permit fee, $100 stormwater review, 2.5% technology fee, $6.50 state fee). A CPI-adjusted 2026 schedule now applies; confirm with the DSC.

Approval ProcessBuilding permit plus a certificate of occupancy from the Development Services Center, 3rd floor City Hall (SMC 17C.300.120); no land-use hearing or design review. Mechanical, electrical and plumbing permits are separate. The ADU uses the principal dwelling's utilities and street address (SMC 17C.300.130(C)).
Review TimelineThe city publishes no ADU-specific review time. State law (RCW 36.70B.080(1)(d)) makes 65 days from a complete application the default for permits that need no public notice, unless Spokane has adopted its own periods; ask the Development Services Center (509-625-6300).
Permit FeesAbout $2,000-$3,200 in city fees for a $150,000-$300,000 ADU (2025 New SFR/ADU fee table: $65 processing, plan review at 50% of the permit fee, $100 stormwater review, 2.5% technology fee, $6.50 state fee). A CPI-adjusted 2026 schedule now applies; confirm with the DSC.
Impact FeesTransportation impact fees apply to new dwelling units by service area (SMC 17D.075; schedule in 17D.075.180, Ordinance C36514, indexed up to 5% a year). State law caps an ADU's fee at 50% of the single-family fee (RCW 36.70A.681(1)(a)). The current dollar figure was not readable; ask the DSC for your service area's rate.
Plan CheckPlan review is 50% of the building permit fee for new single-family, ADU and duplex permits and is paid at submittal before the plans are routed (2025 Development Services Fee Schedule); for a $200,000 ADU that is $736 of a $2,416 total.
Pre-Approved PlansNone found. The city's residential permit pages (August 2026) list an ADU building-permit application but no city pre-approved ADU plan set; the fee schedule offers a stock plan review fee (25% of the job-value fee) for repeat plans, so ask whether a builder's repeat design qualifies.

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Construction Costs [16][17]

Building an ADU in Spokane typically costs $130,000-$260,000 ($200-$400 per sq ft); a garage conversion runs $50,000-$120,000.

See what this means for your lot — ask Spokane ADU builders for a quote →

Average Build Cost$130,000-$260,000
Cost per Sq Ft$200-$400
Garage Conversion$50,000-$120,000
Prefab ADU (Installed)$135,000-$280,000

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Rental Income Potential [18][19]

A 2-bedroom ADU in Spokane rents for around $1,300-$1,500/mo, an estimated 5-11% gross rent yield: HUD FY2027 fair market rents of $1,173 (1BR) to $1,494 (2BR) a month on a $130,000-$260,000 build, before vacancy, taxes and upkeep.

Avg Rent (1 Bedroom)$1,050-$1,250/mo
Avg Rent (2 Bedroom)$1,300-$1,500/mo
Short-Term RentalAllowed with a short-term rental permit under Chapter 17C.316 SMC, but once a lot with an ADU has a short-term rental, one unit must be owner-occupied for more than six months a year and cannot be rented (SMC 17C.300.110.
Est. Annual ROI5-11% gross rent yield: HUD FY2027 fair market rents of $1,173 (1BR) to $1,494 (2BR) a month on a $130,000-$260,000 build, before vacancy, taxes and upkeep

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Recent Law Changes

What's Changed Recently

  • Ordinance C36696 (passed June 2, 2025, effective July 11, 2025) rewrote SMC 17C.300 to comply with HB 1337: two ADUs per lot in RA through RHD, 1,000 sq ft for attached and detached units (up from 800 attached / 975 detached), a 1,200 sq ft footprint and 25 ft height for detached ADUs, 0 ft rear setback on alleys, and an ADU exemption from paved-access street requirements (SMC 17H.010.040(F))
  • Ordinance C36629 (effective March 6, 2025) repealed minimum off-street parking requirements citywide (SMC 17C.230.110), so an ADU needs no parking space
  • Ordinance C36753 (passed October 20, 2025, effective November 28, 2025) amended SMC 17C.300.140 to name the Development Services Department; no change to ADU size, setback or occupancy standards
  • Development Services fees were reset January 22, 2025 after a fee study, with automatic CPI adjustment each January 1 from 2026; the 2026 schedule is posted at static.spokanecity.org (development-fee-schedule-2026.pdf)
  • EHB 1345 (Chapter 231, Laws of 2026, effective June 11, 2026) limits detached ADUs outside urban growth areas; it applies to rural county land and does not change rules inside Spokane city limits
  • State floor since July 2023 (HB 1337, RCW 36.70A.680-.681): two ADUs per lot, at least 1,000 sq ft, 24 ft height, no owner-occupancy, impact fees no more than 50% of the principal unit's, no parking within 1/2 mile of major transit

Tips for Building an ADU in Spokane

  • Alley lots are the sweet spot: a detached ADU may sit on the rear lot line where it abuts an alley (Table 17C.111.205-2), and Spokane requires no parking, so the rear yard is fully usable up to the 1,200 sq ft footprint and the zone's building coverage cap
  • Converting a garage or shed: SMC 17C.300.130(B)(4) lets a structure already inside a rear or side setback become an ADU without being moved, but adding floor area brings the whole building under current setbacks and height (25 ft)
  • Attached ADU threshold: the house must already have 1,000 sq ft of floor area (garage excluded) before you carve out an attached unit; a basement or attic conversion is exempt from the 1,000 sq ft ADU cap (SMC 17C.300.110(A)(1))
  • Second house or ADU? Under SMC 17C.300.100(C) you choose whether a backyard unit is permitted as an ADU (1,000 sq ft, 25 ft, 0-5 ft rear setback) or as a second principal dwelling under the residential-zone standards; pick the path whose limits fit the design
  • Fee worked example (2025 table): a $200,000 ADU pays $65 processing + $736 plan review + $100 stormwater review + $1,472 building permit + $36.80 technology + $6.50 state = $2,416.30, plus separate mechanical, electrical and plumbing permits and any transportation impact fee; valuation is the greater of the contract price or ICC Building Valuation Data
  • ADUs are exempt from the paved-access-to-nearest-paved-street requirement on unimproved rights-of-way (SMC 17H.010.040(F)(1)(a)(i)), and state law bars cities from requiring public street improvements as a condition of an ADU permit (RCW 36.70A.681(1)(l))
  • A Spokane mailing address is not proof you are in the city: the city's own permit page says to check Spokane County's SCOUT property dashboard first; unincorporated Spokane County and Spokane Valley apply their own ADU codes
  • Cost basis (September 2026): avg build cost $130,000-$260,000 for a 500-1,000 sq ft detached unit, from a Spokane planning-level industry guide (detached $110,000-$260,000; 600 sq ft example $130,000-$240,000 including design, permits, sitework, MEP and finishes) and a May 2026 modular guide (installed prefab $200,000-$400,000 nationally, $150-$300 per sq ft). Cost per sq ft $200-$400 spans conversions ($190-$340) and detached new builds ($260-$450); garage conversion $50,000-$120,000; prefab installed $135,000-$280,000. Rents: HUD FY2027 fair market rents for the Spokane HMFA are $1,173 (1BR) and $1,494 (2BR); Zumper's September 2026 medians are $1,050 and $1,325
  • Cost basis (2026-09-20 re-verification): short term allowed: Allowed with a short-term rental permit under Chapter 17C.316 SMC, but once a lot with an ADU has a short-term rental, one unit must be owner-occupied for more than six months a year and cannot be rented (SMC 17C.300.110(B)).

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Sources & References

All data on this page is sourced from official government records and verified market data. View our full methodology.

  1. SMC 17C.300.100 General Regulations (ORD C36696, eff. July 11, 2025) — Spokane Municipal Code Municipal Code — Accessed 2026-09-20
  2. SMC 17C.300.110 Criteria (ADU size, short-term rental occupancy) — Spokane Municipal Code Municipal Code — Accessed 2026-09-20
  3. SMC 17C.300.130 Development Standards (creation, parking, setbacks, height, footprint) — Spokane Municipal Code Municipal Code — Accessed 2026-09-20
  4. SMC 17C.111.205 Development Standards Tables (Tables 17C.111.205-1 and -2) — Spokane Municipal Code Municipal Code — Accessed 2026-09-20
  5. SMC 17C.230.110 Minimum Required Parking Spaces (ORD C36629, eff. March 6, 2025) — Spokane Municipal Code Municipal Code — Accessed 2026-09-20
  6. SMC 17C.300.140 Accessory Dwelling Unit Expiration (ORD C36753, eff. Nov 28, 2025) — Spokane Municipal Code Municipal Code — Accessed 2026-09-20
  7. Ordinance amending Title 17 SMC for HB 1337 (draft as filed with SEPA register; adopted as ORD C36696) — City of Spokane Municipal Code — Accessed 2026-09-20
  8. RCW 36.70A.681 Accessory dwelling units — limitations on local regulation (HB 1337) — Washington State Legislature State Law — Accessed 2026-09-20
  9. SMC 17C.300.120 Application Procedures — Spokane Municipal Code Municipal Code — Accessed 2026-09-20
  10. 2025 Building Permit Fee Table for New Single-Family Residences & ADUs (eff. Jan 22, 2025) — City of Spokane Development Services Center fee_schedule — Accessed 2026-09-20
  11. Development Services Fee Schedule 2025 (plan review percentages, technology fee, CPI adjustment clause) — City of Spokane fee_schedule — Accessed 2026-09-20
  12. Residential Fee Calculators (valuation rule, New SFR/ADU/Duplex estimator) — City of Spokane Planning Department — Accessed 2026-09-20
  13. SMC 17D.075.040 Assessment of Transportation Impact Fees — Spokane Municipal Code Municipal Code — Accessed 2026-09-20
  14. RCW 36.70B.080 Development regulations — time periods for project permit decisions — Washington State Legislature State Law — Accessed 2026-09-20
  15. Residential Permit Process (applications; city-vs-county check) — City of Spokane Planning Department — Accessed 2026-09-20
  16. How Much Does an ADU Cost in Spokane in 2026? — ADUWizard (planning-level industry guide) industry — Accessed 2026-09-20
  17. Modular ADU cost guide (updated May 27, 2026) — Dwelling Index industry — Accessed 2026-09-20
  18. FY 2027 Fair Market Rents schedule — Spokane, WA HMFA — HUD Government Data — Accessed 2026-09-20
  19. Spokane, WA rent research (median asking rents, September 2026) — Zumper Market Data — Accessed 2026-09-20
  20. HB 1337 (2023) bill summary — Washington State Legislature Government Data — Accessed 2026-09-20
  21. EHB 1345 (2025-26) bill summary — Chapter 231, Laws of 2026, effective June 11, 2026 — Washington State Legislature Government Data — Accessed 2026-09-20

Frequently Asked Questions

Can I build an ADU in Spokane?

Yes. ADUs are allowed in All residential zones, RA, R1, R2, RMF and RHD, including planned unit developments; attached or detached (SMC 17C.300.100(A)). In R1, R2, RMF and RHD an ADU may also be added to a lot whose principal structure is non-residential (SMC 17C.300.130(A)(1)(f)). in Spokane. The maximum size for a detached ADU is 1,000 sq ft of floor area (SMC 17C.300.110(A)(2)). Building footprint up to 1,200 sq ft in every residential zone (Table 17C.111.205-2), counted within the lot's total building coverage cap of 50% in RA, 65% in R1, 80% in R2 and 100% in RMF/RHD (Table 17C.111.205-1, note 5).. Owner-occupancy is not required, so you can rent out the ADU.

How much does an ADU cost in Spokane?

ADU construction in Spokane typically costs $130,000-$260,000. Garage conversions run $50,000-$120,000, and prefab ADUs cost $135,000-$280,000.

How much can I rent an ADU for in Spokane?

Average ADU rents in Spokane are $1,050-$1,250/mo for a 1-bedroom and $1,300-$1,500/mo for a 2-bedroom unit.

Do I need parking for an ADU in Spokane?

None. Spokane removed all minimum off-street parking requirements citywide (SMC 17C.230.110, Ordinance C36629, effective March 6, 2025), and SMC 17C.300.130(A)(3) simply refers ADUs to Chapter 17C.230. State law would in any case bar parking mandates within 1/2 mile of a major transit stop (RCW 36.70A.681(2)).. Check with Spokane planning department for the latest Washington ADU parking rules, as many states have relaxed requirements in recent years.

How long does it take to get an ADU permit in Spokane?

Spokane does not publish a standard ADU review timeline. specific review time. State law (RCW 36.70B.080(1)(d)) makes 65 days from a complete application the default for permits that need no public notice, unless Spokane has adopted its own periods; ask the Development Services Center (509-625-6300). Permit fees: About $2,000-$3,200 in city fees for a $150,000-$300,000 ADU (2025 New SFR/ADU fee table: $65 processing, plan review at 50% of the permit fee, $100 stormwater review, 2.5% technology fee, $6.50 state fee). A CPI-adjusted 2026 schedule now applies; confirm with the DSC.

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Spokane ADU FAQ

Answers to every common question about building an ADU in Spokane — costs, rules, permits, rental income.

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Spokane ADU Costs

Detailed cost breakdown: construction $130,000-$260,000, garage conversion $50,000-$120,000, plus ROI analysis.

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Garage Conversion ADU Guide

Complete guide to costs ($80K-$180K), impact fee savings, and permits for garage-to-ADU conversions.

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ADU vs Mother-in-Law Suite

Legal differences that affect what you can build, how you can use it, and rental rights.

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About this information: This page is an informational summary of publicly available regulations - it is not legal, financial, or professional advice, and it is not a substitute for confirming requirements with your local planning department. Rules change frequently; always verify current requirements before designing, budgeting, or building. Last verified: 2026-09-20. Contractors we introduce are independent businesses - verify license and insurance directly before hiring. Spotted an error? Tell us - we verify against primary sources and correct quickly.

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