Zoning & Size Limits
| Requirement | Seattle, WA | Spokane, WA |
|---|
| Allowed Zones | All residential zones (Neighborhood Residential and other re | Single-family residential |
| Max Size (Detached) | 1,000 sq ft of floor area above grade (size also constrained by FAR and lot coverage) | 1,000 sq ft |
| Max Size (Attached) | 1,000 sq ft | 800 sq ft |
| Max Height | Up to 32 ft in Neighborhood Residential and most r | 35 feet |
| Parking Required | Not required (no parking minimum for ADUs) | Studio and 1-bedroom ADUs: none required; larger units subje |
| Owner Occupancy | Not required | Not required (eliminated by Washington HB 1337), except when |
Setback Requirements
| Setback | Seattle, WA | Spokane, WA |
|---|
| Rear Setback | 5 feet | Confirm with Spokane Planning (SMC Title 17C) |
| Side Setback | 5 feet (reduced setbacks allowed along an alley/easement) | Confirm with Spokane Planning (SMC Title 17C) |
| Front Setback | Per zone; DADU generally behind primary structure | Confirm with Spokane Planning (SMC Title 17C) |
Permits & Timeline
| Detail | Seattle, WA | Spokane, WA |
|---|
| Permit Timeline | Several weeks to a few months depending on review queue | 50-75 days |
| Permit Fees | $2,000-$5,000+ in SDCI permit fees (varies with valuation; hourly review rates apply) | $2,000-$3,500 |
| Impact Fees | ADUs exempt from MHA affordability contributions and most im | $600-$1,200 |
| Pre-Approved Plans | Yes — ADUniverse pre-approved DADU plan library | Limited availability |
Construction Costs
| Cost | Seattle, WA | Spokane, WA |
|---|
| Avg Build Cost | $160,000-$320,000 | $110,000-$220,000 |
| Cost Per Sq Ft | $130-$270 | $110-$220 |
| Garage Conversion | $75,000-$170,000 | $50,000-$120,000 |
| Prefab ADU | $110,000-$260,000 | $80,000-$180,000 |
Rental Income Potential
| Rental | Seattle, WA | Spokane, WA |
|---|
| 1BR Avg Rent | $1,600-$2,100/mo | $1,000-$1,450/mo |
| 2BR Avg Rent | $2,000-$2,800/mo | $1,300-$1,900/mo |
| Short-Term Rentals | Allowed with a Seattle STR operator license ($75/yr); a 'sho | Allowed, but owner-occupancy is required when the lot is use |
| Est. ROI | 6-8% annual return | 8-12% annual return |
Which City Is Better for ADUs?
Seattle scores 9/10 while Spokane scores 6/10 on our ADU-friendliness index.
Seattle edges ahead overall. Both cities offer viable ADU development opportunities — the best choice depends on your specific property, budget, and goals.
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