One of the most controversial recommendations from Seattle’s affordable housing task force, or HALA, was to reform zoning laws that only allow single-family homes in certain neighborhoods. That was always going to be a challenge—as Sonia Hirt argues in her history of American zoning, Zoned in the USA, prioritizing and protecting single-family-home-only neighborhoods from other kinds of uses, including multi-family apartments and condos, is possibly the defining feature of American urban planning. Unsurprisingly, opponents launched a campaign warning their fellow single-family-home dwellers of impending doom: multi-story apartments towering over quiet streets, bringing traffic, shadows, and all sorts of unsavory renter types.

But the HALA suggestion was much more modest than that vision of catastrophe. Rather than building highrises, or even midrises, in previously suburban-looking streetscapes, they wanted to allow a kind of housing that’s become practically extinct in many cities: duplexes and triplexes.

Extinct, anyway, in new construction. This kind of mid-density, low-rise housing—including duplexes, triplexes, townhomes, and other low-density multi-family buildings—has been called the “missing middle”: American cities build lots of single-family homes, and (in a certain places) some larger apartment complexes, both in the form of sprawling suburban “apartment communities” and downtown highrises. What we don’t build are the kind of human-scaled, moderately-dense housing that has historically made up the bulk of America’s urban neighborhoods.

Neighborhoods in Chicago, San Jose, and New Orleans with a traditional mix of single-family homes and lowrise multi-family.
Here, for example, is the breakdown of all new construction in the Seattle metropolitan area over the last ten full years:

  And it’s not just a Seattle thing. Cities across the country have the same issue:


Why care about housing’s “missing middle”?

Why does any of this matter? Several reasons. In places where housing prices are an issue, small multi-unit buildings can provide lower-cost housing at market rates—and lower construction costs for nonprofit developers building subsidized housing. These buildings can be placed in single-family districts, many of which are low-poverty “opportunity areas,” without disrupting their lowrise character.

Second, duplexes and triplexes can be a low-visual-impact way to add people to a single-family-home neighborhood. The added density, in turn, can make those communities viable for walkable neighborhood commercial districts, or high-frequency, “show up and go” bus service.

In other words, the “missing middle” is a way to diversify and urbanize low-density neighborhoods without drastically changing the appearance or character of quiet, “suburban”-looking streets that residents of single-family-home areas often value. Charles Marohn of Strong Towns has written about this extensively as a kind of gradual “maturing” of residential neighborhoods, rather than “leapfrog” construction that jumps from mostly single-family homes to midrises or highrises right away.

And missing middle housing can be one key to helping older Americans age-in-place, staying in the same community that they’ve been in, but trading a larger, single family dwelling, for a smaller, but still very much in character unit in a duplex, triplex or other one of these “middle” type housing units.  Many aging baby-boomers live in suburban, single family tracts where there are few alternatives to down-size in their current neighborhoods.  As we’ve noted, all of the net growth in home-ownership in the next two decades is expected to be among households whose heads are aged 65 and older.  Many of these households would no doubt enjoy being owners of smaller scale properties in their own neighborhoods–if they were available.

Of course, denser forms of building are still important. Midrises and highrises allow lots and lots of people to live near major commercial corridors, job centers, and transit hubs, all of which is crucial for giving our cities’ residents economic and social opportunities. High-density buildings also minimize disruption in their own way—a 100-unit highrise downtown might only take up a street corner, but 50 duplexes would take up several whole blocks.

Still, it seems like too many of our cities, including Seattle, have just two settings for urban growth: sprawl and full-on urban density. Figuring out exactly where the roadblocks are to a more moderate kind of density—regulation, financing, and so on—may help keep neighborhoods open to more (and more diverse) people, while respecting the look and feel many residents of relatively low-density communities would like to keep.