Auburn ADU rules
✓ Verified against code · August 20, 2026
Current rules under ACC 18.32 (Accessory Dwelling Unit Development Standards), adopted by Ordinance 6959 §1 (Exh. A), in effect since January 1, 2024. 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.
Common questions, answered from the code
How tall can a detached Auburn ADU be?
24 ft in most residential zones — R-2, R-3, R-4, R-NM and R-F — and 35 ft in the lower-density RC and R-1 zones. A detached ADU counts as an accessory structure, so it takes the accessory-building height from the dimensional table rather than the taller principal-building figure. The 24 ft exactly meets the floor HB 1337 sets; it does not exceed it.
ACC 18.07.030 Table, row H · Permalink
How many ADUs can I build in Auburn?
Two per residential unit, attached, detached, or any combination — provided the lot is individually owned and meets the zone's minimum lot size.
ACC 18.32 · Permalink
Is there a minimum ADU size in Auburn?
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.
ACC 18.32 · Permalink
Do I need parking for an Auburn ADU?
Only if you are more than a half-mile walk from a major transit stop — within that distance no parking is required at all. Beyond it, one on-site space per ADU applies.
ACC 18.32 · Permalink
Do Auburn's ADU rules differ by county?
No. Auburn straddles King and Pierce counties, but it applies its own Title 18 zoning code uniformly citywide, and county code does not govern inside city limits. Which county you are in affects assessor records and some utility providers, not your ADU standards.
ACC Title 18 · Permalink
The rules at a glance
| ADUs allowed per lot | Two per residential unit, on individually owned lots meeting the zone's minimum lot size, and they may be attached, detached, or any combination of the two.ACC 18.32 |
| Maximum size | Between 300 and 1,000 sq ft with a maximum of two bedrooms, excluding garage space. The floor is unusual — most cities set only a ceiling.ACC 18.32 |
| Detached ADU height | 24 ft in the R-2, R-3, R-4, R-NM and R-F zones, and 35 ft in RC and R-1. A detached ADU is an accessory structure, so the accessory-building row of the dimensional table governs rather than the principal-building row.ACC 18.07.030 Table, row H |
| Detached ADU setbacks | Exterior stairs must sit in the rear or side setback and at least 10 ft from an adjoining property line. Rear-setback siting is permitted where the lot abuts a public alley — unless the city routinely plows snow within that alley.ACC 18.32 |
| Off-street parking | None within a half-mile walking distance of a major transit stop; otherwise one on-site space per ADU.ACC 18.32 |
| Owner-occupancy | Not required. A full-text search of the chapter for owner-occupancy language returns nothing.ACC 18.32 (absence verified) |
| Lot coverage / floor area | Auburn controls bulk through maximum impervious area rather than lot coverage or floor-area ratio: 25% in RC, 50% in R-1, 75% in R-2, 80% in R-3, 90% in R-4 and R-NM, and 75% in R-F.ACC 18.07.030 Table, row F |
| Permit path & timeline | An application with a completed form, floor and structural plans, and fees — plus a disclosure statement that must be recorded with the county before final approval. No published review timeline.ACC 18.32 |
Worth knowing
- A disclosure statement must be recorded with the county before an ADU receives final approval — a step several neighbouring cities do not require.
- The alley setback allowance carries a genuinely local caveat: it does not apply if the city routinely plows snow within the alley.
- ADUs may be sold or subdivided as condominiums or through unit-lot subdivision, but a unit split off this way needs its own water and sewer connections.
- A legal nonconforming structure converted to an ADU is not required to come into full compliance.
- Auburn sets a 300 sq ft minimum ADU size as well as the 1,000 sq ft maximum.
On our watchlist
ACC 18.07 shows recent amendments (Ordinances 6977 and 6998 in 2025, Ordinance 7014 in 2026) attached to the chapter's intent section. Whether any touched the dimensional standards that govern ADU height and impervious area is unverified.
Short-term rental limits and ADU impact fees were not found in Title 18; they may sit in Title 5, which was not reviewed.
The exact adoption date of Ordinance 6959 within 2024 is unconfirmed — only the year is cited in the code.
Primary sources
- ACC 18.32 (Accessory Dwelling Unit Development Standards)
- ACC 18.07.030 (residential dimensional standards table)
- City of Auburn Building Services and Permitting
Other Washington cities
Bellevue · Bellingham · Bothell · Burien · Edmonds · Everett · Federal Way · Issaquah · Kent · Kirkland · Lynnwood · Olympia · Puyallup · Redmond · Renton · Sammamish · Seattle · Shoreline · Spokane · Tacoma · Vancouver
Not legal advice. Every fact above cites the code section it comes from — check the cite, or ask your city’s planning department to confirm your specific lot. Spotted an error or a new ordinance? See about to reach us; corrections are logged in the changelog.