Zoning & Size Limits
| Requirement | Seattle, WA | Tacoma, WA |
|---|
| Allowed Zones | All residential zones | Residential zones (most) |
| Max Size (Detached) | 1,200 sq ft | 1,100 sq ft |
| Max Size (Attached) | 1,000 sq ft | 900 sq ft |
| Max Height | 40 feet | 35 feet |
| Parking Required | Optional | Optional |
| Owner Occupancy | Not required | Not required |
Setback Requirements
| Setback | Seattle, WA | Tacoma, WA |
|---|
| Rear Setback | 5 feet | 10 feet |
| Side Setback | 0 feet (easement) | 3 feet |
| Front Setback | 0 feet (alley lot) | 15 feet |
Permits & Timeline
| Detail | Seattle, WA | Tacoma, WA |
|---|
| Permit Timeline | 30-45 days | 40-60 days |
| Permit Fees | $1,800-$2,800 | $1,800-$2,800 |
| Impact Fees | Minimal | $500-$900 |
| Pre-Approved Plans | Extensive library available | Available for common types |
Construction Costs
| Cost | Seattle, WA | Tacoma, WA |
|---|
| Avg Build Cost | $160,000-$320,000 | $135,000-$270,000 |
| Cost Per Sq Ft | $130-$270 | $125-$245 |
| Garage Conversion | $75,000-$170,000 | $65,000-$155,000 |
| Prefab ADU | $110,000-$260,000 | $100,000-$230,000 |
Rental Income Potential
| Rental | Seattle, WA | Tacoma, WA |
|---|
| 1BR Avg Rent | $1,600-$2,100/mo | $1,300-$1,750/mo |
| 2BR Avg Rent | $2,000-$2,800/mo | $1,650-$2,300/mo |
| Short-Term Rentals | Restricted (30 days minimum) | Restricted to primary residence owners |
| Est. ROI | 6-8% annual return | 7-9% annual return |
Which City Is Better for ADUs?
Seattle scores 9/10 while Tacoma scores 8/10 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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