Zoning & Size Limits
| Requirement | San Francisco, CA | Seattle, WA |
|---|
| Allowed Zones | RH-1, RH-2, RH-3, RM, RTO zones and most residential distric | All residential zones |
| Max Size (Detached) | 1,200 sq ft (state minimum; local program caps at 850-1,000 sq ft) | 1,200 sq ft |
| Max Size (Attached) | 1,000 sq ft or 50% of primary dwelling | 1,000 sq ft |
| Max Height | 25 ft for detached ADUs | 40 feet |
| Parking Required | No parking required | Optional |
| Owner Occupancy | Not required | Not required |
Setback Requirements
| Setback | San Francisco, CA | Seattle, WA |
|---|
| Rear Setback | 4 ft minimum | 5 feet |
| Side Setback | 4 ft minimum | 0 feet (easement) |
| Front Setback | Must meet zone's front setback requirement | 0 feet (alley lot) |
Permits & Timeline
| Detail | San Francisco, CA | Seattle, WA |
|---|
| Permit Timeline | 60-day review period (state-mandated) | 30-45 days |
| Permit Fees | $5,000-$20,000 depending on scope | $1,800-$2,800 |
| Impact Fees | Waived for units under 750 sq ft | Minimal |
| Pre-Approved Plans | Yes — SF has pre-approved ADU plan sets | Extensive library available |
Construction Costs
| Cost | San Francisco, CA | Seattle, WA |
|---|
| Avg Build Cost | $200,000-$450,000 | $160,000-$320,000 |
| Cost Per Sq Ft | $300-$500 | $130-$270 |
| Garage Conversion | $120,000-$250,000 | $75,000-$170,000 |
| Prefab ADU | $150,000-$350,000 | $110,000-$260,000 |
Rental Income Potential
| Rental | San Francisco, CA | Seattle, WA |
|---|
| 1BR Avg Rent | $2,200-$3,200/mo | $1,600-$2,100/mo |
| 2BR Avg Rent | $2,800-$4,000/mo | $2,000-$2,800/mo |
| Short-Term Rentals | Heavily regulated; 90-day annual cap for unhosted | Restricted (30 days minimum) |
| Est. ROI | 5-8% annual return | 6-8% annual return |
Which City Is Better for ADUs?
San Francisco scores 9/10 while Seattle 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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