The Missing Middle Housing Reform Sweeping Through City Zoning Codes

A wave of zoning reform aimed at legalizing duplexes, triplexes, and small apartment buildings in traditionally single-family neighborhoods is spreading across cities and states, driven by a shared conclusion that restrictive zoning is a core cause of the housing shortage.

Zoning codes that restrict entire neighborhoods to single-family detached homes have come under sustained pressure from researchers and policymakers who argue those rules are a significant, self-inflicted contributor to housing shortages, by legally prohibiting the small-scale multi-unit housing that once filled the space between a single house and a large apartment building.

Several cities and states have responded by legalizing duplexes, triplexes, and small multi-unit buildings in areas previously zoned exclusively for single detached homes, a category of reform often described as missing middle housing, aimed at filling a gap in housing types that zoning had effectively eliminated over previous decades.

Legalizing it doesn’t guarantee it gets built

Early results in cities that have implemented these reforms show real but modest uptake so far, since construction costs, financing availability, and local permitting processes still shape whether developers actually build the newly-legalized housing types at meaningful scale, independent of the zoning change itself.

“Changing the zoning code is a necessary step. It is not, by itself, a sufficient one. You still need someone willing and able to build.”

Supporters of the reforms generally view them as one necessary piece of a larger housing affordability strategy rather than a complete solution on their own, with construction cost, financing, and local permitting speed all remaining significant factors in how much new housing actually results from the zoning changes over time.