Zoning & Size Limits
| Requirement | Seattle, WA | Spokane, WA |
|---|
| Allowed Zones | All residential zones | Single-family residential |
| Max Size (Detached) | 1,200 sq ft | 1,000 sq ft |
| Max Size (Attached) | 1,000 sq ft | 800 sq ft |
| Max Height | 40 feet | 35 feet |
| Parking Required | Optional | 1 space per unit |
| Owner Occupancy | Not required | Not required (WA state eliminated this requirement) |
Setback Requirements
| Setback | Seattle, WA | Spokane, WA |
|---|
| Rear Setback | 5 feet | 15 feet |
| Side Setback | 0 feet (easement) | 5 feet |
| Front Setback | 0 feet (alley lot) | 20 feet |
Permits & Timeline
| Detail | Seattle, WA | Spokane, WA |
|---|
| Permit Timeline | 30-45 days | 50-75 days |
| Permit Fees | $1,800-$2,800 | $2,000-$3,500 |
| Impact Fees | Minimal | $600-$1,200 |
| Pre-Approved Plans | Extensive library available | 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 | Restricted (30 days minimum) | Not permitted |
| 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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