Is there a minimum ADU size in Auburn?
✓ Verified against code · August 20, 2026
Yes, and it is worth knowing because most cities don't have one. An Auburn ADU must be at least 300 sq ft and no more than 1,000 sq ft, with a maximum of two bedrooms. Garage space doesn't count toward the total.
Citation: ACC 18.32
How current is this?
Auburn’s ADU rules run under ACC 18.32 (Accessory Dwelling Unit Development Standards) (Ordinance 6959 §1 (Exh. A)). Auburn's ADU chapter dates to Ordinance 6959 in 2024 and has not been amended since — unusual among the cities in this ledger, most of which have amended twice. Auburn spans King and Pierce counties, but applies Title 18 uniformly across both portions; county code does not govern inside city limits. Auburn is also one of the few cities here that sets a minimum ADU size as well as a maximum. We verified this answer against primary sources on August 20, 2026, and every change we catch is logged in the changelog.
More Auburn ADU questions
- How tall can a detached Auburn ADU be?
- How many ADUs can I build in Auburn?
- Do I need parking for an Auburn ADU?
- Do Auburn's ADU rules differ by county?
All Auburn ADU rules → · Compare Washington cities →
Not legal advice — lot-specific overlays can change the answer for your parcel. The citation above points at the governing code section; check it, or ask the city to confirm.