Seattle quietly started counting ADUs against floor-area limits — and the internet hasn’t noticed
✓ Verified against code · August 20, 2026
Ordinance 127376 struck Seattle’s interim ADU floor-area exemption effective January 21, 2026. Seven months later, leading AI answers and most published guides — including some updated after the change — still describe the repealed rule.
Before January 21, 2026 (interim 2025 code)
ADU gross floor area was exempt from floor-area-ratio (FAR) limits in Neighborhood Residential zones — the provision that made two units pencil on small lots, carried in the May 2025 HB 1337 package (Ord 127211).
Since January 21, 2026 (Ord 127376 / CB 120993)
ADU floor area counts toward FAR, and ADUs count toward density. Lot coverage runs 50% in NR zones, with FAR set by a density-based table (0.6–2.0). A two-ADU plan now has to be modeled against the lot’s full FAR budget before assuming both units fit.
When Seattle adopted its permanent state-compliance zoning in December 2025 (Council Bill 120993, signed as Ordinance 127376, effective January 21, 2026), it repealed the old Chapter 23.44, renumbered half the residential code — and struck the interim rule that had exempted ADU floor area from FAR limits. The change is easy to miss: the ordinance is best known for its middle-housing provisions, and the ADU consequence sits in amended cross-references rather than a headline section.
Missed it is exactly what the information ecosystem did. When we tested the question "does a backyard cottage count against floor-area limits in Seattle?" in August 2026, both trained AI models and live search-grounded AI answers confidently answered no — citing the repealed exemption. Guides published in 2025 describe the interim rule; at least one prominent architect’s guide updated in May 2026 still doesn’t mention the change. The repeal has almost no web footprint.
The practical stakes are real. On a 5,000 sq ft NR-zone lot, FAR and the 50% lot-coverage cap now bind a house-plus-two-ADUs plan that would have cleared under the exemption. Anyone who penciled a project on 2025-era advice — or on an AI answer — should re-model before design money is spent. Two details survive as good news: up to 250 sq ft of attached garage and underground stories stay out of the ADU size math, and pre-existing accessory structures keep their conversion exemptions.
This page exists because rule changes with quiet paper trails are where published answers rot fastest. We verified the repeal against the signed bill text, re-verified it adversarially, and we re-check Seattle’s code on every pass — any further amendment lands in our changelog the week we catch it.