In parts of Arlington where townhouses are currently allowed, they often look something like these, north of the Ballston Metro. The new missing middle rules won’t allow this pattern of development because some of the units don’t face the street, among other reasons. Photo by the author.

Arlington County has become the latest jurisdiction to cast off single-family zoning, legalizing up to six units on residential lots starting July 1. This is the latest step for a county that has generally been accepting of urban growth compared to peer jurisdictions, but has historically failed to allow densification in most of its single-family neighborhoods which occupy the majority of its land area. County officials have described the practice to reap the benefits of growth in limited areas while walling off most neighborhoods as a “pact,” one that’s given way for a more inclusive future.

Other recent missing middle reforms have so far delivered an underwhelming amount of new housing. In some ways Arlington conditions are more supportive of missing middle being built and in other ways less so, so the amount of construction we’ll see remains to be seen.

What will the new rules allow?

Across the county, residential lots will be allowed to accommodate duplexes, three townhouses, or multiplexes with up to six units. In general, missing middle buildings can be as large, and as tall as what’s currently allowed for single-family homes, plus a 5% bonus. Arlington uses height, setback, and lot coverage limits to regulate the size of single-family houses. On small lots, these rules combined allow a new house to be roughly the same square footage as its lot, so a missing middle structure on a 6,000 square foot lot can be close to 6,000 square feet.

In Arlington, single-family houses are allowed to be much larger than what’s allowed in Minneapolis or Portland. Fundamentally, the concept of “the same box with more units” is more viable in Arlington than in other places that only permit relatively small “boxes.” Arlington has a median house price 50% higher than Portland’s and double Minneapolis’, so its larger housing supply shortfall will also incentivize more missing middle construction. A county study using 2019 data finds that the average new single-family house in Arlington was 4,750 square feet and sold for $1.7 million. Missing middle will allow for smaller new houses with smaller yards that sell for less.

However, a tangle of rules still threaten the feasibility of widespread missing middle infill in Arlington. Unlike some other localities that have legalized missing middle, Arlington requires parking for these new units. Missing middle units within three-quarters of a mile of a Metro station or half a mile of a stop on a Premium Transit Network will be required to have 0.5 spots per unit, while units elsewhere in the county will be required to have 1 spot per unit.

Further, the rules limit how this parking can be provided. The interior width of garage walls may not make up more than half of a building’s street-facing facade. Only two surface parking spots are allowed between a building and the street on smaller lots and three spots between a building and the street on larger lots. The parking requirements combined with limits on how parking can be provided may put a squeeze on construction.

The rules require all new missing middle units to be oriented toward the street, limiting how builders can fit new units on existing lots. Like many suburban jurisdictions, Arlington is full of deep lots without alley access. In this context, infill housing oriented toward a shared driveway, like slot houses or Houston townhouses, just makes geometric sense, but the Arlington rules won’t allow them.

These townhomes in Clarendon, shown in 2008, face a courtyard. Arlington's new rules would require homes to face the street. Image by Dan Reed.

Following Portland’s lead, Arlington has imposed gross floor area caps that vary depending on the number of units in a missing middle structure. The intent seems to be to encourage builders to provide smaller, less expensive units in multiplexes rather than larger townhouse-style units. Relative to Portland’s caps, they are large, ranging from 4,800 square feet for an up-down duplex to 8,000 square feet for five or six units, compared to 3,000 square feet to 6,000 square feet in Portland.

Unlike Portland, however, which caps single-family houses at 2,500 square feet, Arlington has no gross floor area cap for single-family houses beyond what height, lot coverage, and setback requirements dictate. On some small lots, single-family houses will be permitted to be slightly larger than duplexes, and on large lots, in some cases, single-family houses can be larger even than five- or six-plexes. The viability of missing middle thus depends on the premium for square feet divided across multiple units being larger than the return to more square footage that homebuilders can get from building larger single-family houses.

On top of these limits, the county has imposed an annual cap of 58 lots being converted to missing middle housing in the program’s first five years. The 58 permits have to be spread across large, medium, and small lots. From a market perspective and a planning perspective, it makes the most sense for missing middle units to be built in the county’s most amenity-rich neighborhoods close to transit but where everything other than single-family housing has been prohibited historically. But the cap requiring more than one-third of missing middle permits to be issued on large lots mean that some of them can only be built in the far reaches of the county.

Anti-townhouse bias

What’s missing in Arlington? Relative to many peer jurisdictions, Arlington has allowed a lot of multifamily construction, resulting in a relatively large supply of small studio, one- and two-bedroom units. But there’s a big leap both in price and square footage between renting one of these apartments and buying a house in the county’s single-family neighborhoods. Reducing this gap requires starter-home construction, which missing middle is intended to facilitate.

Relatively small units in multiplexes would be the least expensive type of missing middle, but they’d also have to compete more directly with apartments and condos in the county’s large multifamily buildings. In other high-cost jurisdictions, like DC, we see that new missing middle construction tends to be owner-occupied rather than rental. For owner occupied housing, fee-simple ownership is generally preferable to condo ownership if possible because it enables lower-cost financing for construction and mortgages, and it means the owners can avoid dealing with the headaches of shared ownership down the road.

It’s likely that the type of missing middle construction that will be most attractive to Arlington home builders and homebuyers are units similar to townhouses that are bigger than typical high-rise units, smaller than new detached single-family units, and well-suited for owner-occupancy.

In some ways, Arlington’s rules support this type of construction well. Unlike Minneapolis, for example, Arlington allows lot splits for new side-by-side duplexes or groups of three townhouses. In other ways, the rules stymie the type of townhouse construction that’s already working in Arlington. Townhouses with tuck-under parking can’t be built with the missing middle limitations on garages. Frequently townhouse developments include units oriented parallel to their lot lines, as shown above. The missing middle rules require all units to be facing their lot line, so this won’t be allowed either. We’ve commonly seen that missing middle reforms don’t legalize already-existing missing middle, and Arlington’s is no exception.