Urban Wire A Framework for Analyzing How Different Zoning Approaches Can Allow for More Housing
Andrew Trueblood
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The United States has a growing national housing shortage, which research has shown is connected to restrictive zoning. Policymakers and advocates nationwide are evaluating zoning changes that could allow for more housing, such as eliminating single-family zoning, increasing transit-oriented development, and increasing the “missing middle” housing typology of small apartments. But the various and often overlapping approaches can make it challenging to compare policy changes’ potential effectiveness and make a data-driven case for moving forward with the right reforms.

When I directed the DC Office of Planning, we were tasked with changing our land-use map to support more housing and had to decide where best to focus additional potential density. We ended up focusing on providing more density along major corridors that already allowed for multifamily housing, but a more robust comparative analysis would have been helpful in conversations with communities and stakeholders. As such, developing a framework for quantitative analysis of the effects of different zoning changes is vital for supporting an outcome-oriented, evidence-based approach to our land-use and housing challenges.

Building a comprehensive way to structure analyses of zoning reforms

To fill this analysis gap, the Urban Institute recently published a report comparing existing and potential zoning changes for transit-accessible housing throughout the Seattle region. To model the effects of potential zoning changes on housing production across various jurisdictions with a wide variety of land uses, the analysis synthesized upzoning approaches into four mutually exclusive and collectively exhaustive categories:

  1. “Plexify”: Allowing up to four units on existing single-family parcels.
  2. “Missing Middle”: Allowing up to 12-unit apartment buildings on existing parcels with four units or less.
  3. “Multiply”: Doubling the allowed density of multifamily housing parcels.
  4. “Legalize”: Allowing residential buildings on commercial parcels that currently restrict housing.

These categories focus on upzoning or increasing density allowances but don’t include other potential zoning changes that could allow for more housing, such as parking-minimum reductions. Because the analysis spanned across the region mapping parcel-level zoning, it showed how these approaches could yield more housing in different types of communities across the Puget Sound region. By looking at every location close to transit, including both urban and suburban areas, the analysis illustrates that every single community can support more housing using one of the four reforms.

Many communities are debating allowing for two-, three-, or four-unit “plexes” in areas that have required single-family housing. The analysis quantifies how this change could be effective in the Puget Sound, especially in communities that have the most restrictive zoning rules. At the same time, the analysis shows that additional density in an urban context through the “multiply” reform could yield the most significant amount of additional housing. In other communities, the “legalize” reform—by allowing housing in areas that do not allow it now, such as strip shopping centers with large parking lots—could yield significant additional housing in transit-rich areas.

The policy potential moving forward

The quantitative analysis paints a compelling picture of which types of zoning changes could best add much-needed housing to specific communities, but the discussions that dictate the addition of this housing historically happen at the community and block level. Often, proposed upzoning ends with opposition to changes in “neighborhood character.”

To demonstrate how each of these reforms could integrate into the existing neighborhood, the framework also provided archetype visualizations. Providing illustrations of how each reform could look and feel will help community members understand how these reforms could respect and support neighborhood context. The framework could also help the growing range of state governments that want to make changes demonstrate how changes would affect their communities while minimizing negative effects.

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Illustrations showing new housing with missing middle (left) and legalize zoning reforms.
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By outlining the reform options and aligning the most effective regional reforms with the neighborhood context (including visualizations), the report provides a framework for policymakers at various levels to facilitate better conversations and refute common arguments against zoning reforms. At the state level especially, opponents claim that zoning reforms are a one-size-fits-all approach, which the framework dispels, instead offering a better understanding of the options and ultimately better outcomes.

Already, this analysis has been used to guide legislation in Washington State and has supported conversations in the Puget Sound region about zoning reforms. When I directed DC’s Office of Planning, this report would have been a vital tool for working with policymakers, advocates, and residents to plan for more housing. Hopefully, this framework can be a model for future analysis in other states, regions, and localities who are considering how to address their systemic housing shortages.

Research Areas Neighborhoods, cities, and metros
Tags Housing affordability Housing markets Infrastructure Land use and zoning Multifamily housing Transportation
Policy Centers Metropolitan Housing and Communities Policy Center
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