Spokane County, WA Accessory Structures: ADU Rules (2026)
ADU rules in Spokane County, WA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Units per lot
- One ADU per single-family lot
- Detached size cap
- 800 sq ft ground floor
- Attached size cap
- 35% of area or 900 sq ft
- Bedrooms
- No more than 2 bedrooms
- Min lot (detached)
- 10,000 square feet
Summary
Spokane County allows one accessory dwelling unit (ADU) per single-family lot. Detached ADUs are capped at 800 sq ft on the ground floor and 2 bedrooms, on lots of at least 10,000 sq ft. Attached ADUs are capped at 900 sq ft.
The accessory dwelling unit shall contain no more than 2 bedrooms and shall measure no more than 800 square feet on the main (ground) floor. Only 1 accessory dwelling unit shall be allowed per lot with an existing single-family residence. Accessory dwelling units shall not be allowed on lots that are less than 10,000 square feet in size.
Full Breakdown
Under Spokane County Zoning Code Chapter 14.606 (LDR, LDR-P, MDR, HDR zones), a detached ADU may contain no more than 2 bedrooms and measure no more than 800 sq ft on the main (ground) floor, needs a pitched roof (min 4:12 slope, ridge under 24 ft), and is not allowed on lots under 10,000 sq ft. An attached ADU must not exceed 35% of the building's livable floor area nor 900 sq ft, whichever is less, and must keep the single-family appearance. Only one ADU is allowed per lot, and it can't be combined with a duplex or multi-family use. One extra off-street parking space is required. Detached ADUs are a conditional use requiring Hearing Examiner review.
Violations & Fines
ADUs built without required conditional-use approval or building permits are zoning-code violations enforced by Spokane County Building and Planning; correction or removal may be ordered.
Frequently Asked Questions
How big can a detached ADU be in Spokane County?
Do I need extra parking for an ADU?
Sources & Official References
Other rules in Spokane County
How Spokane County compares: Easiest Cities to Build an ADU·Compare Spokane County to another location·View the Washington accessory structures overview
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