Zoning & Size Limits
| Requirement | Tacoma, WA | Bellevue, WA |
|---|
| Allowed Zones | Residential zones (most) | Any lot in a land use district that allows a single-family d |
| Max Size (Detached) | 1,000 sq ft living area | 1,200 sq ft (Director may approve more for single-floor units in the primary structure or conversions/additions to existing accessory structures) |
| Max Size (Attached) | 1,000 sq ft living area | 1,200 sq ft, or 40% of the structure, whichever is greater |
| Max Height | 35 feet | Detached ADUs: 24 ft to the highest point (28 ft w |
| Parking Required | Not required (per Washington HB 1337) | None under 1,000 sq ft; 1 space for 1,000-2,000 sq ft; none |
| Owner Occupancy | Not required | Not required (removed by Ordinance 6746 in 2023; prohibited |
Setback Requirements
| Setback | Tacoma, WA | Bellevue, WA |
|---|
| Rear Setback | 15 feet (no setback required from an alley) | Subject to middle-housing dimensional standards (LUC 20.20.538) — Confirm with Bellevue Development Services |
| Side Setback | 5 feet (8 feet if the main entrance faces the side property line) | Subject to middle-housing dimensional standards (LUC 20.20.538) — Confirm with Bellevue Development Services |
| Front Setback | Per underlying zone; Confirm with Tacoma Permits | Per underlying district / middle-housing standards |
Permits & Timeline
| Detail | Tacoma, WA | Bellevue, WA |
|---|
| Permit Timeline | 40-60 days | Several weeks to a few months depending on review queue — Confirm with Bellevue Development Services |
| Permit Fees | $1,800-$2,800 | Permit and plan review fees based on project valuation — Confirm with Bellevue Development Services |
| Impact Fees | $500-$900 | School/transportation impact fees may apply; HB 1337 caps AD |
| Pre-Approved Plans | Available for common types | No city pre-approved plan library — Confirm with B |
Construction Costs
| Cost | Tacoma, WA | Bellevue, WA |
|---|
| Avg Build Cost | $135,000-$270,000 | $180,000-$380,000 |
| Cost Per Sq Ft | $125-$245 | $200-$350 |
| Garage Conversion | $65,000-$155,000 | $90,000-$190,000 |
| Prefab ADU | $100,000-$230,000 | $120,000-$280,000 |
Rental Income Potential
| Rental | Tacoma, WA | Bellevue, WA |
|---|
| 1BR Avg Rent | $1,300-$1,750/mo | $2,500-$2,900/mo |
| 2BR Avg Rent | $1,650-$2,300/mo | $3,100-$3,900/mo |
| Short-Term Rentals | Restricted to primary residence owners | No citywide STR ban identified — Confirm current short-term |
| Est. ROI | 7-9% annual return | 6-8% annual return |
Which City Is Better for ADUs?
Tacoma scores 8/10 while Bellevue scores 8/10 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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