Washington ADU Permits

Spokane ADU Permits & Requirements

Fees $2K–$3.5K · 50–75 day review · Up to 975 sf detached · Two ADUs per lot

Quick Answer

Spokane ADUs: $150K–$310K

Permits: $2K–$3.5K · Updated April 2026

Permit Fees Breakdown

Fee Type	Cost	Notes
Building Permit	$1,000–$2,500	Based on project valuation
Plan Review	$500–$1,200	City of Spokane plan check (~2–3 weeks)
Impact Fees	$600–$1,200	Capped at 50% of single-family rate (HB 1337)
Utility Connections	$2,000–$8,000	Water, sewer, electric; higher for a rear detached unit

Permit Process Timeline

Pre-Application & Feasibility

1–2 weeks

Use the City's free Middle Housing Support Team to confirm your lot allows an ADU (or two)

Plan Preparation

2–4 weeks

Architectural plans meeting City of Spokane code plus snow-load engineering

Building Permit Review

50–75 days

City review for building code, zoning, and Washington State Energy Code compliance

Construction

4–8 months

Build phase with required framing, electrical, plumbing, and insulation inspections

Final Inspection & CO

1–2 weeks

Final inspection and Certificate of Occupancy

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Zoning & Requirements

Max ADU Size

975 sf detached

ADUs Per Lot

Up to 2 (HB 1337)

Rear Setback

0 ft w/ alley

Parking

None (studio/1-bed)

Key Regulations

Washington HB 1337 (2023) requires up to TWO ADUs per lot in most residential zones — any mix of attached and detached
No owner-occupancy required — unless the property is operated as a short-term rental
ADU impact fees capped at 50% of the single-family rate under HB 1337
No off-street parking required within 1/2 mile of a transit stop; studio and 1-bed ADUs exempt
Detached max 975 sf (or 75% of the primary building); internal/attached max 800 sf
Rear setback 0 ft with an alley, 5 ft without — verify with Spokane Planning (SMC Title 17C)

Climate & Construction Notes

Spokane's cold, snowy climate drives real code costs: roof and framing engineered for the local design ground snow load (commonly cited around 39 psf — verify for your site), frost-protected footings below Spokane's frost depth (roughly 24 inches), freeze-protected plumbing, and Washington State Energy Code insulation and air-sealing. Factor these into your structural and materials budget — they are not optional upgrades.

Frequently Asked Questions

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

The typical City of Spokane review is 50–75 days on a complete submittal, with plan check often 2–3 weeks. Total project time including design and construction is usually 6–12 months.

What types of ADUs are allowed in Spokane?

Spokane allows detached ADUs up to 975 sf, attached/internal ADUs up to 800 sf, plus garage and daylight-basement conversions. Under HB 1337 you may build up to two ADUs on one lot.

Do I need to live on the property to build an ADU in Spokane?

No. HB 1337 bars Washington cities from requiring owner-occupancy, except when the property is used as a short-term rental. Check with the City of Spokane for the most current requirements.

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