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 (Neighborhood Residential and other re |
| Max Size (Detached) | 1,200 sq ft (state minimum; local program caps at 850-1,000 sq ft) | 1,000 sq ft of floor area above grade (size also constrained by FAR and lot coverage) |
| Max Size (Attached) | 1,000 sq ft or 50% of primary dwelling | 1,000 sq ft |
| Max Height | 16 ft for a detached ADU in the rear yard (state f | Up to 32 ft in Neighborhood Residential and most r |
| Parking Required | No parking required | Not required (no parking minimum for ADUs) |
| 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 | 5 feet (reduced setbacks allowed along an alley/easement) |
| Front Setback | Must meet zone's front setback requirement | Per zone; DADU generally behind primary structure |
Permits & Timeline
| Detail | San Francisco, CA | Seattle, WA |
|---|
| Permit Timeline | 60-day review period (state-mandated) | Several weeks to a few months depending on review queue |
| Permit Fees | $5,000-$20,000 depending on scope | $2,000-$5,000+ in SDCI permit fees (varies with valuation; hourly review rates apply) |
| Impact Fees | Waived for units under 750 sq ft | ADUs exempt from MHA affordability contributions and most im |
| Pre-Approved Plans | Yes — SF has pre-approved ADU plan sets | Yes — ADUniverse pre-approved DADU plan library |
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 | Not allowed — SF ADUs and JADUs are ineligible for the Short | Allowed with a Seattle STR operator license ($75/yr); a 'sho |
| 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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