Burien ADU rules

✓ Verified against code · August 19, 2026

Current rules under BMC 19.17.070 (Burien Municipal Code, post-Ordinance 868), adopted by Ordinance 868, in effect since July 9, 2025. Ordinance 868 — Burien's comprehensive Title 19 rewrite for HB 1110/1337 — took effect July 9, 2025. Fair warning: the city's own ADU handout (last updated May 2024) still shows the pre-868 rules, including an 800 sq ft detached cap that no longer exists.

Common questions, answered from the code

How big can a detached ADU be in Burien?

1,000 sq ft — same as attached and internal ADUs. If you've seen 800 sq ft, that's the city's own May 2024 handout, which predates Ordinance 868 and hasn't been updated. The ordinance controls.

BMC 19.17.070(2)(C) (Ord 868) · Permalink

Do I need parking for a Burien ADU?

No — the code says flatly that no parking is required for ADUs, anywhere in the city, with no transit-distance condition. (Cite-checkers beware: the provision moved from subsection (1)(D) to (1)(C) when Ordinance 881 re-lettered the section in late 2025.)

BMC 19.20.045(1)(C) · Permalink

How tall can a Burien DADU be?

Genuinely unclear — and worth a direct question to the city. There's no ADU-specific limit, and the accessory-structure formula (primary's height + 10 ft, max 35 ft) could compute below the state's 24-ft minimum on a low house. Ask Burien Community Development for a written answer for your lot; we track this conflict on our watchlist.

BMC 19.17.060(2)(B) · Permalink

I have an unpermitted ADU — can I make it legal?

Yes. Burien's code provides an explicit legalization path: apply for the applicable permits and bring the unit into compliance.

BMC 19.17.070(3) · Permalink

What utility work should I budget for?

More than most cities: a separate sewer connection for any ADU type, a separate electric meter, possibly a separate water meter for new construction — plus sprinklers if you're building over 1,500 sq ft or two stories.

City ADU handout · Permalink

The rules at a glance

ADUs allowed per lot	Two ADUs per lot, with no restriction on the attached/detached mix — allowed accessory to a single detached home in any zone, or to middle housing in a Residential zone.BMC 19.17.070(2)(A)–(B)
Maximum size	1,000 sq ft for internal, attached, AND detached ADUs. The director may grant size exceptions to better use existing spaces in buildings at least five years old. (The 800 sq ft detached cap in the city's old handout is the pre-2025 rule.)BMC 19.17.070(2)(C)
Detached ADU height	No ADU-specific height limit. Residential accessory structures are capped at 10 ft above the primary residence's existing height or the zone's maximum height (35 ft in residential zones), whichever is less — and the code doesn't expressly say whether that formula binds DADUs. On a low single-story house it could compute below the state's 24-ft floor, an unresolved conflict we're tracking.BMC 19.17.060(2)(B); RCW 36.70A.681
Detached ADU setbacks	New DADUs meet zone standards (front 20 ft, interior 5 ft in RS-7,200) — except a detached ADU may sit at the rear lot line where it abuts an unplowed public alley. Conversions of existing structures are exempt from setbacks and lot coverage.BMC 19.17.070(2)(D)(i)–(ii)
Off-street parking	None. 'No parking is required for ADUs' — unconditional, citywide, beyond what HB 1337 required.BMC 19.20.045(1)(C) (enacted at (1)(D) by Ord 868, re-lettered by Ord 881, 2025)
Owner-occupancy	None — Burien removed owner-occupancy back in 2019 (Ord 724), and the current code carries no trace of it.BMC 19.17.070 (verified absence)
Lot coverage / floor area	70% impervious-surface coverage in RS-7,200; accessory structures are limited to the lesser of 15% of lot area or 80% of the primary structure's footprint (minor deviations allowed). ADU conversions are exempt from lot coverage.BMC 19.15.005; 19.17.060(2)
Permit path & timeline	Building permit under Title 15 — an attached ADU is reviewed as a duplex for building-code purposes. Sewer and water availability certificates plus Fire Marshal flow review are submitted with the application. No published timeline (secondary sources suggest 3–4 months).City ADU handout (building-code items); BMC Title 15

Worth knowing

Unpermitted existing ADUs can be legalized by applying for the applicable permits — an explicit code path.
Separate sewer connections are required for both attached and detached ADUs; separate electric meters are required; water meters may be required for new construction.
Sprinklers are required for new construction over 1,500 sq ft or more than one story.
East of 1st Ave S, airport noise-mitigation construction requirements apply (SeaTac flight path).
Significant-tree retention rules can require a Major Tree Removal Permit before siting a DADU.

On our watchlist

The DADU height question (accessory-structure formula vs. the state's 24-ft floor) is the biggest open item — we recommend written confirmation from Burien Community Development and will log any resolution.

ADU impact fees were not addressed in the Ord 868 text we reviewed — unverified.

The city's ADU handout remains un-republished since Ord 868; watch for a corrected version.

Ordinance 881 (2025) already re-lettered the parking section post-Ord 868 — Burien is amending actively; we re-check Title 19 each pass.

Check your parcel

The rules above are citywide — what you can build depends on your lot’s zone, size, and setbacks. Look yours up on the official viewers:

Primary sources

Other Washington cities

Bellevue · Bothell · Edmonds · Everett · Issaquah · Kent · Kirkland · Lynnwood · Olympia · Redmond · Renton · Sammamish · Seattle · Shoreline · Tacoma

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.