Where the Law Comes From
- HB 1110 (2023) created the middle housing requirements, codified at RCW 36.70A.635 through 36.70A.638.
- ESHB 2321 (2024) adjusted them: it tightened the definition of a major transit stop, set the transit radius at a quarter-mile walk and clarified the parking limits.
- SB 5258 (2023) required cities to offer unit lot subdivision, so middle housing can be sold as individual homes.
Cities in King, Snohomish, Pierce and Kitsap counties had until June 30, 2025 to adopt compliant codes. Where a city falls short, the state's model ordinance applies in place of conflicting local rules.
The Three City Tiers
| Tier | Who | Minimum homes per residential lot | Near major transit (¼-mile walk) | With affordable units |
|---|---|---|---|---|
| T1 | Cities of 75,000+ | 4 | 6 | 6 (if 2 affordable) |
| T2 | Cities of 25,000 to under 75,000 | 2 | 4 | 4 (if 1 affordable) |
| T3 | Cities under 25,000 within a contiguous urban growth area that includes the largest city of a county over 275,000 | 2 | — | — |
"Tier" is the Department of Commerce's shorthand; the statute itself describes the three groups by population.
What Counts as Middle Housing
The law lists nine building types, and cities must allow at least six of them:
What Counts as a Major Transit Stop
For middle housing, a major transit stop is a stop on a high-capacity transportation system, a commuter rail stop, a stop on a rail or fixed-guideway system, or a stop on a bus rapid transit route. In our area that means Link light rail stations, Sounder stations and Swift and RapidRide stations. Regular bus stops and ferry terminals do not count. Bus rapid transit stops under construction are treated as major transit stops for the quarter-mile minimums.
Parking Limits
| Lot situation | Most a city can require |
|---|---|
| Within a ½-mile walk of a major transit stop | No off-street parking |
| Lot of 6,000 sq ft or less | 1 space per home |
| Lot over 6,000 sq ft | 2 spaces per home |
The lot-size test uses the lot as it existed before any unit lot subdivision or split.
Standards Cannot Be Stricter Than for a House
A city may not apply dimensional, infrastructure or environmental standards to middle housing that are stricter than those for detached single-family homes — including setbacks, lot coverage, stormwater, clearing and tree retention rules. Where a city uses design review, it must be administrative rather than a hearing-based process.
What the Law Does Not Change
How Middle Housing Differs From ADUs
ADUs (accessory dwelling units) are governed by a separate law, HB 1337, and are secondary units attached to a primary home. Middle housing is a set of primary homes. Some cities count ADUs toward the middle housing unit total and some do not.
What This Means for Your Lot
Start with your city's tier, then check walking distance to the nearest major transit stop, then check site conditions. The quickest way to do all three is the lot tool → What Can I Build?