The Transect, a model form-based zoning system based on urban intensity rather than what goes on inside buildings. Image by Duany Plater-Zyberk & Company used with permission.

Zoning is the single most important power in deciding what buildings can and cannot be built, and where. To solve the housing shortages that plague America's cities, zoning will need an overhaul. That overhaul would be more likely if cities had a guide.

Zoning rules the landscape

All over the United States, in virtually any city of any size, zoning rules the landscape. These few seemingly mundane chapters of city code decide how tall buildings can be, what sort of uses can occupy them, how much of a yard they must have, how many people can live in them, sometimes even obscure things like what sort of fonts can go on business signs.

But existing zoning, by and large, is written to exclude. Zoning codes list out strict rules for what kind of development is allowed, and everything else is off limits. And in most cities, the majority of land is reserved for single-family housing. As a result, many cities face a "scarcity of zoned units," meaning they have plenty of land but the zoning does not allow enough housing units to meet demand.

To solve that, people in the YIMBY movement often talk about upzoning—taking a property (or a neighborhood) and changing its zoning to allow denser buildings. The problem is, that strategy turns every property into a zoning battle, every development becomes a prolonged civic engagement struggle. It takes a lot of energy that advocates have to repeat over and over. And it doesn't accomplish enough to solve the overall scarcity.

Meanwhile, since development can only happen in small areas, and since advocates have to struggle for every rezoning, most new development that does happen takes the form of very large buildings, leaving out the kind of "missing middle" small apartment buildings that are best at providing affordable middle class housing.

American cities need a lot more of these.  Image by Google used with permission.

To really enact large-scale change, reform the zoning system that's responsible for the base problem. In particular, reform zoning to allow small apartment buildings in a much larger area of the city, where they're outlawed today.

Obviously that kind of large-scale reform is a heavy lift. Maybe it's impossible. But there's at least one good step the YIMBY movement could take in 2018 to move in that direction: Write an ideal model zoning code from the ground up, to offer to cities for their own use as a guide.

Model zoning codes have worked before

This idea doesn't side-step the difficulty of reform. Convincing cities to adopt new zoning is no easy task.

But it has worked twice before. Much of the zoning that's in place today is the result of model codes that advocates offered up, and made it easy for cities to adopt.

Model codes were instrumental in the original spread of zoning through the mid-Twentieth Century. Towns, particularly fast-growing suburban ones, would buy a model code and adopt it for themselves.

Model zoning codes made suburban development the law of the land. Public domain image by Daniel Lobo.

Then more recently, with the growth of New Urbanism in the 1990s and early 2000s, it happened again. New Urbanist firms like the famous Duany Plater-Zyberk & Company (DPZ) found that existing zoning outlawed the type of communities they were trying to build, so they offered up New Urbanist-friendly replacements like the now open-source DPZ SmartCode.

Countless American cities adopted them as part of their zoning, if not as complete replacements. That fueled the growth of infill and suburban town centers all over the country.

Obviously New Urbanism has not completely replaced traditional suburban development. But there is a lot of it around the country, and model codes have been instrumental in making it happen.

Model codes also legalized New Urbanist developments, like Kentlands, MD. Image by the author.

What would a model YIMBY zoning code look like?

What would YIMBY zoning actually say? Presumably it would be form-based rather than use-based, meaning it would base different zoning categories primarily on the size and look of buildings rather than on what the inside of buildings are used for, (e.g. "commercial" or "residential").

That sort of zoning is fairly common, if not exactly ubiquitous. Among many examples, Arlington uses it along Columbia Pike, and Sarasota, Florida is considering it this year.

An excerpt from Sarasota, Florida's form-based code. Image by City of Sarasota.

Beyond their form-based structure, YIMBY zoning would presumably focus on walkable urbanism. For example, urban zones would have minimal-if-any setback or parking requirements. In this regard, a YIMBY zoning system would look a lot like New Urbanist SmartCodes.

But YIMBY zoning would need to be different from New Urbanist zoning in other key ways, to accommodate the scale of housing development our cities need.

Upzoning triggers would legalize urban evolution

A key concept that YIMBY zoning might include would be triggers that automatically upzone properties once they pass some threshold.

California's recent (but defeated) SB 827 proposal would have used the presence of high-quality transit nearby as a trigger to upzone core parts of San Francisco and Los Angeles. That's one potential trigger method.

Another is land value. If land in a lower-intensity zone passes a certain price threshold—perhaps 150% the median value per acre for that zone citywide—it's automatically upzoned to the next more intense zone.

Another method could be housing affordability itself: If housing inside a certain radius becomes too expensive compared to incomes, all land inside that radius bumps up one intensity zone.

There are any number of potential triggering methods, each with its own positives and negatives. What's important is the triggering concept itself, whereby city zoning is reformed to automatically evolve based on changing conditions.

Or at the very least, to make building enough homes easier. SB 827 proposed state control over what's now local zoning, which might be one way to get enough homes built. Japan takes that idea even further, with national zoning laws. Another intriguing method proposed by London YIMBY would make zoning decisions hyper locally, at the block-by-block level, to give landowners a more direct financial incentive to zone for more housing.

To make this happen, research the details

As with all things, the devil is in the details. It's all well and good to publish a blog post suggesting America needs upzoning triggers, but what should they actually look like?

Actually developing a model code would be a big project. It would take the resources of an entire firm, including economists, city planners, lawyers, and more.

But the pay-off could be substantial, both for any firm that completes the project and for American cities more broadly. A model code could help spread the legal underpinning for YIMBYism in a new and highly-effective way. And, like the DPZ SmartCode, it could become the tent-pole product for a planning firm hoping to make a name for itself.

What do you think YIMBY zoning should include? Tell us in the comments.

Credit for the model zoning idea goes to Bjorn Swenson. Credit for the triggering idea goes to Dan Keshet.

Tagged: housing, yimby, zoning

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Dan Malouff is a transportation planner for Arlington and professor of geography at George Washington University, but blogs to express personal views. He has a degree in urban planning from the University of Colorado and lives in northeast DC. He runs BeyondDC and contributes to the Washington Post .