How big can a detached ADU be in Burien?
✓ Verified against code · August 19, 2026
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.
Citation: BMC 19.17.070(2)(C) (Ord 868)
How current is this?
Burien’s ADU rules run under BMC 19.17.070 (Burien Municipal Code, post-Ordinance 868) (Ordinance 868). 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. We verified this answer against primary sources on August 19, 2026, and every change we catch is logged in the changelog.
More Burien ADU questions
- Do I need parking for a Burien ADU?
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All Burien 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.