How Multifamily Housing Gets Approved in Seattle

Washington State requires Seattle to allow middle housing on residential lots under House Bill 1110, layered on top of the city's Mandatory Housing Affordability program and a 2025 state law for housing near transit stations. Seattle's design review program, long paired with the Master Use Permit process, is temporarily voluntary while the city drafts permanent rules. The facts below come from the Revised Code of Washington and the City of Seattle's own construction and land use pages, read as of October 2026.

Middle housing under HB 1110

Washington's HB 1110 (2023) sets minimum density tiers for cities planning under the Growth Management Act (RCW 36.70A.635). For cities with population over 75,000, including Seattle, the law sets this floor:

• At least four units permitted on every residential lot.
• At least six units permitted on lots within one quarter mile of a major transit stop.
• At least six units permitted on lots where at least two of the units are affordable housing, maintained as affordable for a term of at least 50 years.

The statute also limits how cities can regulate middle housing: development standards may not be more restrictive than those required for detached single-family houses, only administrative design review may be required, and cities may not require off-street parking within one-half mile of a major transit stop (RCW 36.70A.635). Seattle adopted zoning for its Neighborhood Residential areas to meet these state requirements as part of the One Seattle Plan comprehensive plan update, with the required changes effective in 2025.

Mandatory Housing Affordability

Seattle's Mandatory Housing Affordability (MHA) program applies when the City Council approves a rezone that raises the maximum height or floor area ratio, or changes the zoning designation, in areas marked with an MHA suffix in the Land Use Code (SMC 23.58B for commercial zones, SMC 23.58C for residential zones). A developer in an MHA area chooses one of two paths: build a share of units onsite as affordable housing, the performance option, or pay into the city's affordable housing fund, the payment option.

The Seattle Department of Construction and Inspections (SDCI) program page lists current MHA payment amounts through February 28, 2027, and treats the program as an active permitting requirement. No primary source read today shows MHA has been invalidated. New areas rezoned under the One Seattle Plan, including land along transit arterials and in neighborhood centers, are also subject to MHA.

Station area housing under HB 1491

HB 1491 (2025) is in force. The governor signed it May 13, 2025; it became Chapter 267, Laws of 2025, and took effect July 27, 2025, codified mainly at RCW 36.70A.840. It applies to cities planning under the Growth Management Act, including Seattle. Within a station area, generally lots within one-half mile of a rail station entrance or one-quarter mile of a qualifying bus rapid transit stop, a city must allow multifamily housing wherever any other residential use is permitted, and must allow an average floor area ratio of at least 3.5 near rail stations and at least 2.5 near bus stations (RCW 36.70A.840). A city may not set a maximum residential density in units per acre within a station area, and a building that is entirely affordable, workforce or permanent supportive housing for at least 50 years receives an additional 1.5 floor area ratio. Most station area buildings must hold a minimum share of affordable or workforce units for at least 50 years, subject to listed exceptions. Cities must adopt conforming local regulations on a schedule tied to their comprehensive plan update cycle, generally by December 31, 2029, or the state's model ordinance takes over in that city.

Design review and the Master Use Permit

A Master Use Permit, issued by SDCI, is the city's land use approval for new multifamily buildings. Design review has historically been a component of that permit for larger multifamily and mixed-use projects, with a board-level track for the largest projects and a faster track for townhouses and small multifamily buildings.

As of this review, mandatory design review in Seattle is suspended. Washington's HB 1293 (Chapter 333, Laws of 2023) required statewide changes to local design review programs by June 30, 2025. In response, Seattle City Council adopted interim rules, in place since September 2025, that make design review voluntary while permanent legislation and new design guidelines are prepared; those interim rules have been renewed, most recently at a Council hearing in July 2026. A project can still choose design review, but it is not currently a required step before Master Use Permit approval in Seattle.

Questions

Is Seattle's design review currently mandatory?

No. Since September 2025, participation has been voluntary under interim City Council rules responding to Washington's HB 1293 (Chapter 333, Laws of 2023). Seattle has been renewing those interim rules while it writes permanent legislation.

Has Washington's station area transit housing law taken effect?

Yes. HB 1491 was signed May 13, 2025, and took effect July 27, 2025, as Chapter 267, Laws of 2025, codified mainly at RCW 36.70A.840. Cities, including Seattle, must adopt conforming local regulations on a set deadline.

Is Seattle's Mandatory Housing Affordability program still in effect?

Yes, based on Seattle's own program page, which lists current payment amounts through February 28, 2027. No primary source reviewed here shows the program has been invalidated.

Sources