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Increasing Local Housing Supply Through Missing Middle Housing

Image credit: Steve Butler

Local governments throughout Washington State are wrestling with the issue of affordable housing. For some communities experiencing high growth rates, it may be an issue of how to accommodate an increased number of housing units. For others, it may be the desire to create a variety of housing options to accommodate the differing needs and household income levels of all residents.

One direct method to allow for more residential growth is to “upzone” land to accommodate a greater amount of housing (i.e., change the zoning of some land from a lower to a higher density level, such as from single-family to medium-density multi-family zoning). This approach is usually controversial, with the public often being concerned about the compatibility of multi-family buildings right next to single-family homes.

As an alternative, several communities are looking at other, less dramatic methods to encourage a type of residential infill development that is lower scale than mid-rise multi-family housing and intended to be more compatible with adjacent properties. This is when “missing middle housing” may be an option worth considering.

This blog is the first of a two-part series, with the first describing some of the different types of missing middle housing (MMH), while the second will provide more details on the actions that local governments may take to encourage MMH within their communities.

What is Missing Middle Housing?

MMH fills the gap between single-family residences and mid-rise, multi-family development and includes the following housing types:

  • New housing on small lots
  • Duplexes, triplexes, and fourplexes
  • Townhouses,
  • Cottage housing
  • Courtyard housing
  • Live/work units

missing middle housing diagram

Image Credit: © Opticos Design, Inc. | Missing Middle Housing term created by Daniel Parolek | For more information visit

More communities in our state are exploring MMH as an approach for increasing the diversity of housing options in their communities. While MMH will not address the housing affordability needs of lower income households, MMH units are typically more affordable to moderate income households (for example, 80-100% area median income, or AMI) than more traditional single-family housing units.

If you are interested in increasing your community’s housing supply by promoting neighborhood-compatible infill development in your community, the following options are some MMH approaches to consider.

New houses on small, existing lots


Image credit: Steve Butler

In most communities, there are always existing lots created prior to current minimum lot size standards, with the result being that they are nonconforming. Instead of having those small lots stand vacant, some cities have taken steps to encourage development on them.

Duplexes, triplexes, and fourplexes


Image credit: Steve Butler

Duplexes, triplexes, and fourplexes provide the opportunity for smaller scale residential development to fill in the gaps between a mid-rise type of multi-family development and single-family residential areas. The units can be side-by-side or stacked on top of one another. Good design can soften the visual impact of the extra number of dwelling units.

The photograph above is an example of a well-designed residential fourplex that would visually fit in and be accepted within most single-family neighborhoods.

Gig Harbor’s Design Manual includes design standards for duplexes (as well as for other residential types).


Photograph of rowhouses

Image credits: City of Shoreline

In certain parts of the U.S., a large percentage of a city’s multi-family dwelling units are made up of townhouses. Until recently, this housing type has not historically been as popular in Washington State.

Townhouses are usually individual dwelling units (on their own parcels of land) that share walls with other residential units, have front stoops/porches and backyards, and are typically owner-occupied. To maximize a positive connection with the surrounding neighborhood, it is important that townhouses be oriented towards the public street (for example, having the primary entrances doors face the street and not towards an interior parking area).

The cities of SeaTac and Wenatchee have good townhouse regulations.

Cottage housing


Greenwood Avenue Cottages, Shoreline WA. Photo courtesy of The Cottage Company

Cottage housing usually consists of a grouping of small, single-family dwelling units clustered around a common outdoor space and developed as part of a master site plan.

Early successful examples of this development type may be found in the cities of Langley, Shoreline, and Redmond. More recently, Kirkland has encouraged cottage housing.

Courtyard housing


Image credit: Steve Butler, MRSC

Some cities allow the development of “courtyard apartments,” which consists of several attached dwelling units (either rental or owner-occupied) arranged on two or three sides of a central courtyard or lawn area. This type of housing is usually one or two stories in height and sometimes serve as buffers between arterial roadways and single-family neighborhoods.

Live-work buildings


Image credit: Steve Butler

Small-scale, live-work buildings typically contain one or more residential units either attached or detached from a non-residential space. The non-residential workspaces are usually located on the first floor of a building, have tall floor-to-ceiling heights, and can have a storefront appearance.

Live-work options are good for connecting jobs and housing and may become increasingly popular as more people decide to permanently work from home. The non-residential space also provides an opportunity for more small-scale retail to be provided within or next to an existing residential neighborhood.

Tacoma is one of several cities that are encouraging this development type.

What about accessory dwelling units?

Accessory dwelling units (ADUs) are an important type of infill residential development but are often not categorized as fitting within the MMH definition. This situation is primarily due to ADUs being located on a residential lot with an existing single-family home (and therefore not within the “missing middle” area between single-family and multi-family residential zones.

General Methods for Encouraging MMH

Here are a few ways that local governments can encourage the construction of MMH:

  • Change your regulations: This step could include revising your zoning code to allow MMH in more locations within your community.
  • Revise your permitting procedures: It is important that your development project review procedures for MMH proposals (and other types of development projects as well) be clear and user-friendly, which will make it easier for both applicants and permit staff to successfully navigate the development review process.
  • Provide educational information: The reasons for encouraging MMH development should be clearly articulated and explained to the public, to address any concerns that people may have about this type of housing. Many communities, such as Bellingham’s Infill Housing Toolkit and Tacoma’s tip sheet on live-work units, have easy to understand guidebooks and information on their websites.
  • Consider financial incentives: If your community has enacted a Multi-Family Tax Exemption (MFTE) program, consider whether some types of MMH would be eligible for your MFTE program and determine whether there is a good public policy reason to do so. Other financial incentives may be available for MMH development with units affordable to lower-income households.
  • Offer pre-approved plans: This approach has been gaining popularity for encouraging ADUs and some communities are now exploring using the same approach for MMH. The City of Wenatchee is considering creation of pre-approved plans for some types of MMH.

The Washington Department of Commerce’s Growth Management Services Division administers a Middle Housing grant program to local governments in King, Kitsap, Pierce, and Snohomish counties, and recently hired three experienced planners (Shane Hope, Dave Osaki, and Joe Tovar) to provide resources and technical assistance to help encourage new moderate-density, middle housing options within Washington State.

Conclusion and Webinar Invite

Taking steps to increase options for infill development by a local government may sound easy, but that is usually not the case. Neighborhood concerns about density, increased traffic, and parking impacts are likely to be voiced. Development costs for these new types of infill development may be greater than expected, resulting in a low number of units being constructed.

If you want to diversify your housing options and/or accommodate new residents into your community, exploring ways to achieve well-designed infill development is an important task to undertake. Specific strategies and actions that local governments can take to encourage MMH will be the subject of a future blog. However, if you are interested in hearing more about this topic, you may wish to register for our Making “Missing Middle” Housing Work in Washington State webinar, scheduled for September 27, 2022, 12:00-1:30 p.m. It will feature speakers with the cities of Bellingham, Kirkland, Olympia, Spokane, and Wenatchee.


MRSC is a private nonprofit organization serving local governments in Washington State. Eligible government agencies in Washington State may use our free, one-on-one Ask MRSC service to get answers to legal, policy, or financial questions.

Photo of Steve Butler

About Steve Butler

Steve joined MRSC in February 2015. He has been involved in most aspects of community planning for over 30 years, both in the public and private sectors. He received a B.A. from St. Lawrence University (Canton, New York) and a M.S. in Urban and Regional Planning from the University of Wisconsin-Madison. Steve has served as president of statewide planning associations in both Washington and Maine, and was elected to the American Institute of Certified Planner’s College of Fellows in 2008.