New Law: Making Missing Middle Housing


So your big house is feeling just a little too big? And those hip urban villages seem just a little too edgy? Where to go? How about a nice bit of “middle housing”? If all goes well over the next 18 months, the region should see a surge in construction of attractive new homes aimed at neglected segments of the market.

In its last session, the Washington Legislature passed the most significant housing legislation in a generation. House Bill 1110 requires that at least 77 cities in Washington, including all cities in the Seattle urbanized area, change their zoning codes to allow significant increases in densities in single family areas. In addition, House Bill 1337 mandates that all cities in the state, as well as unincorporated areas inside urban growth lines, allow at least two accessory units on a single family lot. 

What is middle housing? 

Diagram of missing middle housing types showing the scale between single-family homes and mid-rise buildings. (Opticos Design on Flickr)

Middle housing fills the gap between the two primary types of housing we have: single-family homes, and large multi-family complexes. HB 1110 specifies nine types of middle housing, at least six of which must be allowed: duplex, triplex, fourplex, fiveplex, sixplex, townhouse, stacked flat, courtyard apartments, cottages. This is a bit of an apples/oranges list, since the “-plexes” can be configured as townhouses, stacked flats, or courtyard apartments. But the idea is clear: a lot of proximity and common walls.

The size of the city determines how much more density it will be required to allow, with small and medium sized cities having to allow two units where one is allowed now and large cities having to allow four units on a single lot. Midsized and large cities must also allow bonus units if some units are kept affordable or the project is near a transit station.

The bill tries to head off loopholes cities might try to exploit. Parking requirements and development regulations are hemmed in and only administrative design review is allowed. Current restrictions by homeowners’ associations are grandfathered in, but new restrictions are not allowed. New codes in the Puget Sound area must be in place by June 30, 2025, or the state will impose its own code language.

Within the housing market, middle housing offers the chance to live in a quiet neighborhood setting without the large investment in a traditional single family house. New housing being built in the region consists overwhelmingly of large multi-family complexes in busy urban settings, and not everyone is attracted to that lifestyle.

Middle housing has the potential to free up single family homes and get them into the hands of young families. In the Seattle metro area, 63 percent of households over age 65 live in detached housing that they own, and one quarter of all homeowners over age 65 live alone. Middle housing offers those older homeowners a chance to downsize to a smaller, newer, ground-related home while staying in their neighborhood.

The really big deal 

The truly radical part of the bill is the provision that cities must allow existing single family lots to be legally subdivided so that cottages and attached homes can be sold as fee-simple properties (stacked flats can be sold as condos). This constitutes a huge theoretical expansion of buildable land for ownership housing.

There is ample evidence that lot size is just not that important to homebuyers, and suburban lots have been shrinking for years. Through the 1980s, 10,000 square foot (roughly quarter acre) lots were common, and single family parcels rarely fell below 7,200 square feet. Since the advent of growth management, 4,000 square foot lots have become common for detached homes, and attached homes come with even smaller parcels. 

So splitting an old 10,000-square-foot lot presents few marketing difficulties, and putting a duplex on a split 7,200-square-foot lot seems quite feasible. Cottages in clusters have always had small footprints, but now can be sold on individual lots rather than as condos.

The ability to create new lots offers the potential to greatly expand ownership opportunities for ground-related homes for those who have been frozen out of the market by high prices. This provision also allows land-rich-cash-poor households to turn a large backyard into instant cash.

How, exactly, the economics of land prices plays out is unknown, since we don’t know how many property owners will be eager to sell off parts of their property and how many properties will come on the market for full redevelopment. We also don’t know how aggressively builders will be seeking those opportunities. But it would be reasonable to assume that the abundance of potential new lots will have at least some depressing effect on lot prices.

A long way to go 

To get from this promising legislation to large scale construction of new middle housing a lot of things have to go right. Local codes must be written so that builders find attractive opportunities and can work profitably at a small scale. The kinds of small local builders who got washed out 15 years ago need to be lured back. And these small projects will need new, creative-financing tools. A subsequent article at Post Alley will flesh out these and other challenges that lie ahead for local governments and the housing industry.

Michael Luis
Michael Luis
Michael Luis is a public policy consultant who has been wrestling with housing, growth and economic development issues around Washington State for over 30 years. He is author of several books on local history and served as mayor of Medina.


    • Love it – one triplex per block. So our block has 8 triplexes out of 14 lots, and the other 6 are 2s. Can we get the city to opt us out of the coming 65′ high no-setbacks from the property lines rules that are coming when they write the requirements for the 6x housing in 1110? Because we also have significant solar on our block, and we are seeing mulitple 55′ high and 45′ high new housing on Wallingford Ave that are blocking the solar on 30′ high craftsmans.

      What’s not great is those people spent $40k each, plus battery walls.

      Could we get solar installations paid back, as Oregon requires, if a developer blocks any of your solar?

      And all these new $1million to $1.2million townhouses (SF + Adu + DADU) took out a ton of trees.

      And the city and various developer-paid-YIMBYs suggest we have quality transit, when 1 year ago we had our only bus reduced 70% (in terms of frequency and carriage capacity). So everyone who was taking the bus to work (a dozen people on our block) stopped and started driving.

      Seems like there are a few things to consider here, before we just willy nilly get 3s on every block (BTW all the surrounding blocks around us have 2s at min and +3s on every block. But they also have trees and solar.)

      Or actually 6s — the 1110 number of houses when you have “quality transit” — one bus per hour in each direction during the day. 6s are allowed on each lot now, without parking, and upzone for that to make developers more profitable, and take out all the remaining trees. And yet we know from watch the neighbors, that each and every person living here, with a job, will have a car. On the street.

  1. I continue to believe that the City Council massively screwed up when, as apodment construction was booming, it tightened regulations on their construction to the point that it completely choked off new construction of those micro-apartments. There was (obviously) a huge market for them.

  2. This isn’t more density, it’s less.

    Seattle’s existing zoning, designed by local urban planners instead of developer lobbyists in Olympia, is based on an “urban village” concept – focusing development around a set of urban core areas, along with the transportation and services they need to offer a somewhat urban settlement pattern.

    That’s density – literally, a higher population density in some places than others, because Seattle has been allowed to use zoning to make that happen. Mass transit, pedestrian access, the kind of thing we used to supposedly care about as the attractive part of higher population density.

    It’s true that Seattle has been short on housing … despite 10-15,000 units a year every year. Seattle will continue to be short of housing if it keeps growing the way it did in the preceding decade, because there isn’t any kind of zoning that’s going to bring on significantly more development. But now, thanks to Olympia, Seattle will have to give up on density. Development will surely take advantage of the windfall represented by lots newly available for multifamily housing and build market rate housing far away from the nearest shopping and transportation, and Seattle will take one more step towards being just another expensive West Coast city, this time with a distinctly California style. I’m so glad I’m just reading about this from afar.

  3. This seems akin to closing the barn door after the horse escaped. Remote work just completely changed the economics of how the housing market works in Seattle. There used to be this huge pull of talent to office jobs here — talent that that earned very high incomes. That no longer is happening. Indeed, that tide is ebbing with all the layoffs. That lack of future demand for housing, coupled with higher interest rates suggests the hoped-for “missing middle” demographic cohort that would occupy ‘plexes throughout Seattle won’t materialize.

  4. Attractively presented argument, (though thin on evidence ) and blissfully neglects any mention of how these new lot sizes you like so well are ruining Seattle’s famous tree canopy….the feature of living in the Northwest that has always set this region apart. I can understand why developers are rubbing their hands together.


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