ADU rules in Auburn, WA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Auburn permits ADUs and DADUs under ACC 18.31.120 per WA HB 1337. Up to two ADUs per lot, max 1,000 sq ft, no owner-occupancy rule. Unit lot subdivision for fee-simple sale is allowed.
Auburn City Code Section 18.31.120 regulates Accessory Dwelling Units (ADUs) and Detached ADUs (DADUs). Washington HB 1337, effective 2024, preempted restrictive local ADU rules in cities over 25,000 population; Auburn updated ACC 18.31.120 in 2024-2025 to comply. Under current rules: ADUs and DADUs are allowed in all residential zones that permit single-family dwellings including R-1, R-5, R-7, R-10, R-16, R-20, and RR; up to two ADUs per lot (any combination of attached and detached); maximum unit size 1,000 sq ft or 60 percent of the primary dwelling, whichever is greater; no owner-occupancy requirement; no additional off-street parking requirement within one-half mile of major transit; 4-foot side and rear setbacks for DADUs; maximum 24-foot DADU height. Short-term rental use (under 30 days) is permitted subject to STR registration. Unit lot subdivision allows fee-simple sale of each ADU on its own lot. All ADUs require a building permit, water-sewer connection fees, impact fees (reduced per HB 1337), and must meet Auburn Design Standards. The Auburn Community Development Department processes ADU permits with expedited review.
Contact your local code enforcement office for specific penalty information.
Auburn, WA
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Side-by-side rule comparisons with other cities in King County.
See how other cities in King County handle adu rules.
See how Auburn's adu rules rules stack up against other locations.
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