Auburn, WA · Zoning rules · Updated 2026
Auburn, WA ADU Rules & Build Options
Auburn follows WA HB 1337 (two ADUs per lot, 1,000 SF each). South King County market with lowest land basis in our coverage area.
The rule
Washington state law requires cities to allow ADUs up to 1,000 SF on residential lots.
Source: WA HB 1337 §3 — Auburn tracking state floor (verify local code)
How big can your ADU be?
| Primary dwelling | Maximum ADU size | ADU as % of primary |
|---|---|---|
| 1,000 SF house | 1,000 SF | 100% |
| 1,500 SF house | 1,000 SF | 67% |
| 2,000 SF house | 1,000 SF | 50% |
| 2,500 SF house | 1,000 SF | 40% |
| 3,500 SF house | 1,000 SF | 29% |
Sizes reflect the code rule only. Site-specific setbacks, coverage limits, and overlay zones may reduce buildable envelope further.
Analyze your specific Auburn property
Drop an address to see the exact ADU size your lot allows, plus fourplex, cottage cluster, and middle-housing options. Includes construction cost estimates, exit values, ROI, and cited code sections for every constraint.
Analyze a Auburn addressBeyond the ADU rule
Setbacks + lot coverage
Each zoning district has its own front, side, and rear setbacks plus a lot-coverage cap. Our analyzer applies your zone’s actual limits automatically.
Parking requirements
Many jurisdictions have reduced ADU parking mandates under state law. We flag when your lot requires additional parking spaces.
Overlay zones
Historic districts, floodplains, and design-review overlays can override base zoning. We check the current overlay map for your specific address.
SDCs + permit fees
System Development Charges vary by jurisdiction and ADU size. Fees included in our cost estimates.