Seattle allows up to two ADUs, attached (AADU) or detached (DADU), on any lot where a house is allowed. California state law does not apply here.[1]
| Size limits | Up to 1,000 sq ft gross floor area per ADU. Not counted: up to 250 sq ft of attached garage, exterior-only storage, underground stories and up to 35 sq ft of bike parking.[2] |
|---|---|
| Height | Neighborhood Residential zones: same height limit as the main house. Lowrise zones: the rowhouse and townhouse limit for the zone.[2] |
| Setbacks | Neighborhood Residential: a DADU may sit in the rear yard at least 5 ft from any lot line not on an alley. No setback is required from a lot line on an alley.[2] |
| Parking | |
| Owner occupancy | Not verified. We did not find this on the official pages we checked. Ask the city before you design. |
| Permit steps and timeline | ADUs are permitted through SDCI and must meet city building, energy, land use and critical-area codes. SDCI reports ADU permits to King County for sewer capacity charges.[1] |
| Fees | Not verified. We did not find this on the official pages we checked. Ask the city before you design. |
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Sources
Every fact above links to an official city or state page. Rules change; check the source before you build.
- [1] Seattle SDCI: Accessory Dwelling Unit checked Oct 2026
- [2] Seattle: SMC 23.42.022 as effective June 30 2025 checked Oct 2026
- [3] Seattle OPCD: NR zone standards (Jan 2026) checked Oct 2026