Zoning & Size Limits
| Requirement | Seattle, WA | Portland, OR |
|---|
| Allowed Zones | All residential zones | All residential zones |
| Max Size (Detached) | 1,200 sq ft | 800 sq ft or 75% of primary (whichever is less) |
| Max Size (Attached) | 1,000 sq ft | 1,000 sq ft |
| Max Height | 40 feet | 20 ft (outside setbacks); 15 ft (within setbacks) |
| Parking Required | Optional | Optional |
| Owner Occupancy | Not required | Not required |
Setback Requirements
| Setback | Seattle, WA | Portland, OR |
|---|
| Rear Setback | 5 feet | 5 feet |
| Side Setback | 0 feet (easement) | 0 feet with easement |
| Front Setback | 0 feet (alley lot) | 0 feet (alley lot) |
Permits & Timeline
| Detail | Seattle, WA | Portland, OR |
|---|
| Permit Timeline | 30-45 days | 30-45 days |
| Permit Fees | $1,800-$2,800 | $1,500-$2,500 |
| Impact Fees | Minimal | Minimal |
| Pre-Approved Plans | Extensive library available | Extensive pre-approved library available |
Construction Costs
| Cost | Seattle, WA | Portland, OR |
|---|
| Avg Build Cost | $160,000-$320,000 | $150,000-$300,000 |
| Cost Per Sq Ft | $130-$270 | $125-$250 |
| Garage Conversion | $75,000-$170,000 | $70,000-$160,000 |
| Prefab ADU | $110,000-$260,000 | $100,000-$240,000 |
Rental Income Potential
| Rental | Seattle, WA | Portland, OR |
|---|
| 1BR Avg Rent | $1,600-$2,100/mo | $1,400-$1,900/mo |
| 2BR Avg Rent | $2,000-$2,800/mo | $1,800-$2,600/mo |
| Short-Term Rentals | Restricted (30 days minimum) | Yes, with registration |
| Est. ROI | 6-8% annual return | 6-9% annual return |
Which City Is Better for ADUs?
Seattle scores 9/10 while Portland scores 9/10 on our ADU-friendliness index.
Both cities offer viable ADU development opportunities — the best choice depends on your specific property, budget, and goals.
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