The single biggest reason the Missing Middle has declined is that it is literally illegal in most places. This can be true even in urban neighborhoods that have a lot of duplexes or small apartment buildings: in many of these neighborhoods, zoning codes were changed in the 1960s or 1970s to prohibit the new construction of anything other than single-family homes. The older apartments that are part of the neighborhood's fabric are grandfathered in, but can't be replaced or imitated.

Fortunately, there's a movement to re-legalize the kind of eclectic neighborhoods, with a variety of home types for ownership and rental, that we used to build nearly everywhere. The city of Minneapolis and the whole state of Oregon are prominent examples of places that have recently passed laws to make normal neighborhoods legal again.

2. Make Sure the Rest of Your Zoning Code Isn't Putting Up Obstacles.

Even if non-single-family uses aren't banned in your neighborhood, there are a lot of other ways that cities can make these buildings practically impossible to build. These include setback requirements and minimum lot sizes. In a classic article, Strong Towns contributor Sarah Kobos teaches you how to Kick the Tires on Your Local Zoning Code to figure out what is actually, practically allowed in a given location. You'll likely be surprised by all the barriers.

Backyard Accessory Dwelling Units (ADUs) (which we'll lump in with Missing Middle because they result in two homes on a single residential lot) also face a ton of barriers, sometimes including maximum size or owner-occupancy requirements. These should also be reduced; they create situations where something is legal in theory but nearly impossible in practice.

3. Eliminate Parking Minimums

If you're building a huge building, you can handle the cost of a big parking lot, or even a multi-story parking garage. You can pass this cost—which can be in the tens of thousands of dollars per parking space—on to your eventual renters or buyers. For a small building on a small lot, though, parking quickly becomes prohibitive, as it requires a disproportional share of the lot to accommodate it. And it's rarely all that vital: in a neighborhood with missing-middle housing (as opposed to huge apartment complexes), existing on-street parking is almost always adequate for those who need space for their cars.

There is no reason cities should require building owners to provide more parking than their residents actually need or want. People are more than capable of figuring that out for themselves if you let them. This is why we urge every city in America to end parking minimums.