The Missing Middle Bill 1110 and what it means for Washington State

written by Carmel Gregory, Planner

Recently, House Bill 1110 passed the Washington State legislature and was signed into law by the Governor. This bill would allow at least 2 dwelling units on lots in most cities and in some cases 4 or 6 dwelling units. The bill is informally known as the Middle Housing Bill because it requires cities to implement some of this increase in density through middle housing types.

What is middle housing?

In a nutshell, middle housing types are multi-unit residential buildings that are closer in scale and character to a single-family home than a large apartment building. Examples include duplexes, triplexes, and other multiplexes, courtyard apartments, townhouses, and cottage housing. It is sometimes called “Missing Middle Housing” because in many communities across the United States, there are very few options available between detached single-family homes and large apartment blocks. In the Pacific Northwest, population growth continues at a steady pace, but available land for new housing is becoming harder to find, and rising home costs have delayed or prevented first home purchases. Middle housing is an important tool to help address the housing shortage by providing:

  • Starter homes for people looking to make their first home purchase and enter the housing market
  • More housing density without losing the feel of a residential neighborhood
  • Walkable communities close to employment, shopping, and services
  • Options for retirees and empty-nesters to downsize without necessarily needing to leave their communities
  • More housing options in general, including more rental and purchase options for all types of households

There are many communities that already have middle housing options that don’t look much different than an average detached single-family home. MRSC has a good run-down of what middle housing looks like:

Missing middle housing graphic

What is happening in Washington State?

Currently, a significant portion of urban land in Washington state is zoned for single-family residences, allowing only one dwelling unit per lot. However, House Bill 1110[1] requires most jurisdictions with populations over 25,000 to allow up to 6 dwelling units per lot across the state, with the exact number of dwelling units varying depending on location.

How many residences will be allowed per lot?

The number of residences that will be allowed varies depending on the size of the jurisdiction and the location of the lot:

  • Cities with populations of 25,000 to 75,000 must allow:
    • 2 dwelling units per lot
    • 4 dwelling units per lot within 1/4 mile walking distance of a major transit stop*
    • 4 dwelling units per lot if at least one unit is affordable housing**
  • Cities with populations of at least 75,000 must allow:
    • 4 dwelling units per lot
    • 6 dwelling units per lot within 1/4 mile walking distance of a major transit stop*
    • 6 dwelling units per lot if at least two units are affordable housing**
  • Cities with populations less than 25,000 but that are within a contiguous urban growth area with the largest city in the County with a population of more than 275,000
    • 2 dwelling units per lot

See examples of multi-plex housing at the Washington State Department of Commerce.

*The bill defines a “major transit stop” as a stop for high-capacity transit such as light rail or bus rapid transit.

**Affordable housing, when it’s required to be provided, must be maintained as affordable for at least 50 years. It can be rented or sold as long as it continues to meet the affordability definition.

The Department of Commerce has provided its understanding of the list of cities that must comply with the Middle Housing Bill[2]:

Cities with populations greater than 75k Cities with population between 25k and 75k Cities with populations < 25k contiguous with the UGA of the largest city in a county with population >275k
4-6 dwelling units per lot allowed 2-4 dwelling units per lot allowed 2 dwelling units per lot allowed
Seattle Redmond Kenmore
Spokane Marysville Tukwila
Tacoma Sammamish Mukilteo
Vancouver Lakewood Mountlake Terrace
Bellevue Richland Mill Creek
Kent Shoreline Covington
Everett Olympia Arlington
Renton Lacey Washougal
Spokane Valley Burien Port Orchard
Federal Way Bothell Lake Forest Park
Yakima Bremerton Woodinville
Bellingham Puyallup Newcastle
Kirkland Edmonds Edgewood
Kennewick Issaquah Liberty Lake
Auburn Lake Stevens Fife
Pasco Lynnwood Airway Heights
  Wenatchee Sumner
  Mount Vernon DuPont
  University Place Milton
  Walla Walla Pacific
  Des Moines Fircrest
  SeaTac Normandy
  Maple Valley Steilacoom
  Camas Brier
  Mercer Island Black Diamond
  Tumwater Algona
  Moses Lake Clyde Hill
    Yarrow Point
    Hunts Point
    Beaux Arts


Cities are offered some flexibility in how they implement these rules – for instance, they can delay implementation for some areas that lack infrastructural capacity, are near an airport, have a high displacement risk, or are environmentally sensitive. Cities are not required to allow multiple dwelling units on lots less than 1,000 SF in size. And lots with critical areas and buffers are exempted from these requirements.

Which middle housing options will be allowed?

Cities can decide which housing types to allow, but must allow at least six of the following types:

  • Duplexes
  • Triplexes
  • Fourplexes
  • Fiveplexes
  • Sixplexes
  • Townhouses
  • Stacked flats
  • Courtyard apartments
  • Cottage housing

Cities can also allow accessory dwelling units to be used to meet the residential unit count.

Cities are still allowed to permit detached single-family homes to be built.

When will this happen?

The law will become effective on July 23, 2023, but most Washingtonians may not see the effects of this law until 2025 or later. That is because the law requires local jurisdictions to pass ordinances to comply with the new housing requirement within 6 months after their next comprehensive plan update is issued. Jurisdictions in Snohomish, King, Pierce and Kitsap Counties are required to complete their comprehensive plan updates by the end of 2024, so in those counties, middle housing ordinances may not be passed until mid-2025. Other counties are scheduled to complete their updates in 2025, 2026, or 2027[3].

What are the local jurisdictions doing?

It’s still early, but some local jurisdictions had already been studying how to implement middle housing. See links to information on their efforts here:




City of Snohomish:






What else does HB 1110 do?

It limits how much parking cities can require for middle housing:

  • Cities cannot require off-street parking for middle housing within 1/2 mile walking distance of a major transit stop
  • They cannot require any more than one off-street parking stall per unit for lots smaller than 6,000 SF
  • They cannot require any more than two off-street parking stalls per unit for lots larger than 6,000 SF

It also states that any design review that is applied to middle housing must be administrative only, which means the design of middle housing will not be subject to approval by a design review board.

What can you do as a landowner, homeowner, or developer?

There is a lot that we don’t yet know about how this bill will play out at the local level. Jurisdictions need time to study the requirements and potential impacts and to draft and approve ordinances implementing middle housing. However, if you are interested in this issue, it’s a great time to get involved in your local jurisdiction to help shape how middle housing gets implemented in your community. Contact your local planning department to find out if they have begun studying middle housing, and ask to be put on the notification list for updates. Sign up to be notified of City Council and Planning Commission meetings in your community to keep an eye out for discussion items around housing, and attend or provide input at those meetings.

Eventually, when local ordinances begin to be updated to align with state law on middle housing, CG Engineering can help you determine what you can build and how best to use your property.

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1910 Bickford Ave Suite G Snohomish, WA 98290