The middle-housing law is no longer theoretical.

We've written about what HB 1110 and HB 1337 allow more than once on this blog. What's changed by August 2026 is that the allowing is mostly done. Statewide adoption has passed the tipping point, and Seattle's own rules have been live for over half a year. Here's what's actually buildable now, not what's theoretically coming.

Where implementation actually stands

As of mid-April 2026, 84% of Washington jurisdictions required to comply with HB 1110 have adopted their middle-housing rules. Central Puget Sound cities — King, Pierce, Snohomish, and Kitsap counties — were on the earliest compliance track, with a mid-2025 deadline, so the great majority of the cities in our own service area are past this milestone already. This is no longer a pending policy change to plan around; for most lots we work with, it's the zoning that applies today.

What actually changed in Seattle

Seattle's permanent middle-housing zoning took effect January 21, 2026. The practical result, lot by lot:

• Every Neighborhood Residential lot in Seattle now allows at least four units — a duplex, triplex, or fourplex is legal by right on land that was single-family-only a few years ago.
• Lots within a quarter mile of a major transit stop allow up to six units. That's a meaningfully larger number of Seattle parcels than it sounds — light rail and RapidRide corridors reach deep into neighborhoods that never expected this kind of density.

This sits alongside HB 1337's separate expansion of ADU and detached-ADU rights, which we covered in an earlier post — the two laws stack on the same lot in many cases.

What this means if you already own

If you own a Neighborhood Residential lot in Seattle, or in one of the Eastside cities that adopted on the same timeline, it is worth an actual conversation about what your specific parcel now allows — not a generic one. A DADU addition, a lot split, or a small multiplex conversion can change what a property is worth well beyond what a simple renovation would, and the zoning question that used to require a variance fight now often just requires a permit.

What this means if you're investing

The window where this was priced into very few listings is closing. Eighty-four percent statewide adoption means most sellers, and most agents, now know their lot allows more than it used to — but pricing that in consistently, especially outside the handful of neighborhoods that get attention for it, still lags. That gap is where the opportunity is: a lot valued as a single-family teardown that is legally a fourplex site is not correctly priced, and those mispricings get rarer every quarter as the market catches up.

As always: zoning is applied lot by lot and jurisdictions vary in exactly how they implemented the state minimums. Nothing here substitutes for confirming your specific parcel's allowances with the city before you commit to a plan.

Figures: Washington State Department of Commerce middle-housing implementation tracking, April 2026; City of Seattle Office of Planning & Community Development, HB 1110 implementation guidance.