HB 1110

Key Takeaways

• HB 1110 (2023) is codified at RCW 36.70A.635 and sets minimum residential densities that cities planning under the Growth Management Act must authorize.
• A city of at least 25,000 and under 75,000 must allow at least two units per lot on lots zoned predominantly for residential use, and at least four within a quarter mile walking distance of a major transit stop.
• A city of 75,000 or more must allow at least four units per lot, and at least six within a quarter mile walking distance of a major transit stop.
• Middle housing is a defined term in RCW 36.70A.030 covering nine building types, and a city must allow at least six of the nine to reach the required density.

What It Means

HB 1110 is the 2023 Washington bill that ended single-family-only Zoning as the default in the state's larger cities. It now lives in the Growth Management Act as RCW 36.70A.635, and the operating idea is simple: a city may no longer cap an ordinary residential lot at one house.

The law works through minimum densities rather than through any duty to build. A city has to authorize a set number of units per lot in areas zoned predominantly for residential use, and that number scales with the city's population and with how close the lot sits to transit. What fills those units is middle housing, defined in RCW 36.70A.030 as buildings compatible in scale, form, and character with single-family houses: duplexes, triplexes, fourplexes, fiveplexes, sixplexes, townhouses, stacked flats, courtyard apartments, and cottage housing.

Two points get missed constantly. First, nothing in the statute forces a homeowner to build, and RCW 36.70A.635(9) says nothing in the section prohibits a city from continuing to permit detached single-family houses. Second, the density floor arrives with process relief attached: a city must run middle housing through the same permit and environmental review it uses for a detached house, and it may not impose development standards on middle housing stricter than those it applies to a single house. The wider 2026 picture is in our roundup of Washington market shifts and statutory changes.

How It Works in Washington

RCW 36.70A.635(1) sets the floors by population tier. In a city of at least 25,000 and under 75,000: at least two units per lot on lots zoned predominantly for residential use, rising to at least four within a quarter mile walking distance of a major transit stop, or where at least one unit is affordable housing. In a city of 75,000 or more: at least four units per lot, rising to at least six near a major transit stop, or where at least two units are affordable. The statute also reaches smaller cities. Under RCW 36.70A.635(1)(c), a city under 25,000 that sits inside a contiguous urban growth area with the largest city of a county over 275,000 must allow at least two units per lot.

Affordable units bought with the density bonus are not a one-year promise. RCW 36.70A.635(2)(a) requires them to stay affordable for at least 50 years, secured by a recorded covenant or deed restriction. RCW 36.70A.635(6) then limits the friction a city may add: design review must be administrative only, no development standard may be stricter than the one applied to a detached single-family residence (a city may still apply objective rules such as Setback, lot coverage, stormwater, and tree retention), and no off-street parking may be required within a half mile walking distance of a major transit stop. RCW 36.70A.635(8) exempts critical areas and their buffers and several other narrow categories, and RCW 36.70A.635(11) ties each city's compliance date to its next periodic Comprehensive Plan update, which is why the effective date differs city by city.

Example

The Ortegas own a 7,200 square foot lot in Everett, a city over 75,000, zoned single family before 2023. Under RCW 36.70A.635(1)(b) the city must now authorize at least four units on that lot. Their lot sits about a third of a mile from the nearest bus rapid transit station, so the six-unit tier for lots within a quarter mile walking distance does not reach them. They build a fourplex. Because the lot is larger than 6,000 square feet, the city may require up to two off-street parking spaces per unit. Design review runs administratively rather than going to a board, as RCW 36.70A.635(6)(a) requires. The Ortegas also use a zero lot line short Subdivision, which RCW 36.70A.635(5) requires the city to allow up to the required unit density, so each of the four homes can be sold separately. Their listing broker prices the four units at $529,000 each instead of marketing one $1,050,000 house. Whether that math works depends heavily on the submarket, as our comparison of Washington submarkets shows.

Common Mistakes and Exam Traps

• HB 1110 says what a city must allow, not what an owner must build. RCW 36.70A.635(9) preserves a city's ability to keep permitting detached single-family houses.
• The unit counts are floors, not ceilings. Where existing zoning already permits higher density or intensity, the higher zoning still controls.
• Two units is not the universal answer. The baseline is two units in cities of 25,000 to 75,000 and four units in cities of 75,000 or more, before any transit or affordability bump.
• Middle housing is a defined nine-item list in RCW 36.70A.030, not a loose synonym for apartments, and a city must allow at least six of those nine types.