Case File · Seattle, Washington
Four units per lot.
Adopted unanimously.
Seattle City Council passed the interim HB 1110 middle-housing ordinance unanimously on May 27, 2025 — four units on every residential lot, sixplexes near transit, in time for Washington’s June 30, 2025 deadline.
State fallback would have imposed the Department of Commerce model code. Seattle chose to legislate its own terms — but still meet the mandate.
2023
HB 1110 Enacted
May 21, 2025
Select Committee
May 27, 2025
Council Adoption
Jun 30, 2025
State Deadline
Seattle · 2023-2025
A two-year arc to a unanimous vote.
State mandate plus automatic fallback equals structural pressure. Seattle’s appeals and amendment debates produced delay, not defeat.
2023
Washington enacts HB 1110
The Washington legislature enacts HB 1110, requiring Seattle-tier cities to permit middle housing citywide — duplexes, triplexes, stacked flats, cottage housing, and in Seattle's case four units on all residential lots plus sixplexes near bus rapid transit and light rail.
Early 2025
Comprehensive-plan legal appeals stall the broader growth update
Appeals filed by opponents in Hawthorne Hills, Mount Baker, Madison Park, Montlake, and Madrona neighborhood centers challenge the SEPA review for Mayor Bruce Harrell's 20-year comprehensive plan update. The appeals do not block the HB 1110 interim ordinance but narrow the scope of what can be moved through a single rulemaking.
March 19, 2025
Select Committee begins interim-legislation consideration
The Seattle City Council's Select Committee on the Comprehensive Plan begins considering interim HB 1110 implementation legislation. The interim framing is designed to meet the June 30, 2025 state deadline while deferring the broader comprehensive-plan rework.
May 21, 2025
Select Committee unanimously approves amended interim legislation
The Select Committee on the Comprehensive Plan votes unanimously to approve the amended interim HB 1110 bill. The amendment includes Councilmember Cathy Moore's proposed changes around affordability concerns, alongside the core four-unit and sixplex provisions.
May 27, 2025
Full Seattle City Council unanimously adopts the interim ordinance
The full Seattle City Council votes unanimously to adopt the interim HB 1110 ordinance. Effective before the state's June 30, 2025 deadline. Seattle avoids automatic imposition of the Department of Commerce model code.
June 30, 2025
State compliance deadline satisfied
With the Council's May 27 action, Seattle meets the HB 1110 implementation deadline. The interim ordinance is the near-term middle-housing floor while the comprehensive-plan appeals move through King County Superior Court.
The People Who Decided This Case
State agency. Unanimous council.
Each actor below is documented in the public record — council blog posts, the OPCD memo, and contemporary reporting.
Mayor Bruce Harrell
Mayor, City of Seattle
Seattle, Washington
Documented Record
Executive leadership on both the interim ordinance and the broader comprehensive plan update. The comprehensive-plan appeals target SEPA review of Mayor Harrell's proposal.
Harrell's administration treated the HB 1110 deadline as a non-negotiable constraint. The interim ordinance was designed to preserve executive flexibility on the comprehensive plan while meeting the state mandate on time.
Select Committee on the Comprehensive Plan
Seattle City Council Committee
Seattle, Washington
Documented Record
Unanimous May 21, 2025 approval of the amended interim HB 1110 bill.
Unanimity is the most useful signal here. It tells applicants that the political baseline for middle housing in Seattle is now settled — the fight is over the comprehensive plan, not the four-unit minimum.
Councilmember Cathy Moore
Seattle City Council — At-Large / District 5
Seattle, Washington
Documented Record
Proposed and announced amendments to the interim Middle Housing legislation in May 2025 addressing concerns about rental property ownership.
Moore's amendment work is an indicator of how affordability politics intersect with middle-housing implementation. Her concerns did not block the bill but did shape final language — a pattern worth watching in other HB 1110 cities.
Seattle Office of Planning and Community Development (OPCD)
Implementation Staff
Seattle, Washington
Documented Record
Published the implementation memo describing how the interim legislation satisfies HB 1110 and what the Department of Commerce model-code fallback would have imposed absent local adoption.
OPCD's memo is the authoritative administrative document for applicants. The model-code fallback language is the leverage explanation every developer should read before assuming that local politics can delay HB 1110 compliance.
Hawthorne Hills, Mount Baker, Madison Park appellants
SEPA Appellants — Comprehensive Plan
Seattle, Washington
Documented Record
Six individuals and groups filed appeals challenging the environmental review of Mayor Harrell's comprehensive plan. The Urbanist reported that many of the claims are “likely to be found invalid under state law.”
The appellants target the comprehensive plan, not the interim ordinance. Applicants should separate the two: HB 1110-mandated middle housing stands on its own; the long-range upzones depend on the appeals outcome.
Washington Department of Commerce
State Agency — Middle Housing Model Code
Olympia, Washington
Documented Record
Issued the HB 1110 model code that automatically applies to cities failing to adopt their own implementation by the statutory deadline.
The fallback mechanism is what converts HB 1110 from aspiration to operational. Seattle knew that inaction would produce the Commerce model code — and the Council acted accordingly.
The Pre-Filing Research
What the cited research surfaces in Seattle.
Before the first middle-housing application is filed. Before the comprehensive-plan appeals wind through King County Superior Court.
Jurisdiction Risk Profile
Seattle — Interim Middle Housing
King County, Washington
Applicant-Favorable Conditions
- Four units allowed on all residential lots citywide under the interim ordinance
- Sixplexes allowed near bus rapid transit and light rail stations
- If Seattle had failed to adopt its own code, Washington's Department of Commerce model code would have applied automatically
- Select Committee unanimous approval May 21, 2025; full Council unanimous May 27, 2025
- Comprehensive-plan appeals affect long-term growth questions but not the interim middle-housing floor
Statutory Basis
Washington HB 1110 (2023) — state middle-housing mandate; June 30, 2025 deadline for Seattle-tier cities
Fallback Mechanism
Department of Commerce model code applies if a city fails to adopt — eliminating the “do nothing” off-ramp
Residual Risk
Hawthorne Hills, Mount Baker, Madison Park appeals of the broader comprehensive plan SEPA review remain pending
Approval Pathway
Administrative permit under the interim ordinance; additional design review applies in certain overlays
Precedent Flag
Washington’s HB 1110 follows the Oregon HB 2001 / Minneapolis 2040 pattern: state (or regional) middle-housing mandates with automatic fallback mechanisms if local action fails. The fallback is what changes the leverage profile.
Recommendation
The interim ordinance is the near-term zoning floor. Track the comprehensive-plan appeals separately — they affect long-term upzones, not the HB 1110-mandated minimums.
Source Documentation
All claims on this page are sourced.
Seattle Council Blog — Select Committee approval
Official council blog post confirming unanimous Select Committee approval of the amended interim HB 1110 bill on May 21, 2025.
Seattle Council Blog — Moore amendment announcement
Councilmember Cathy Moore's May 20, 2025 amendment announcement.
Seattle OPCD — HB 1110 implementation memo
Office of Planning and Community Development implementation memo on HB 1110 and the Department of Commerce model-code fallback.
The Urbanist — interim bill coverage
March 12, 2025 coverage of the interim legislation process and comprehensive-plan SEPA appeals.
Capitol Hill Seattle — deadline compliance
Contemporary reporting on the Seattle Council meeting the HB 1110 state deadline and the remaining comprehensive-plan questions.
Hoodline — Unanimous committee vote
Coverage of the May 21 Select Committee unanimous approval.
Cited research summary · Not legal advice · Verify independently before making investment decisions.
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Cited research summary · Not legal advice · Verify independently before making investment decisions