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Urban Economics & Housing Policy

Zoning Laws and Why Housing Costs What It Does

How local rules about what can be built where directly shape housing supply, and therefore housing prices.

Housing prices are ultimately a story about supply and demand, like any other market - but the supply side of housing is shaped by something most other markets don’t have: local laws that dictate, parcel by parcel, exactly what can legally be built. Those laws are called zoning, and understanding them is essential to understanding why housing costs so much in some cities and so little in others, even when demand looks similar on paper.

What zoning actually controls

Zoning laws divide a city into districts and specify what’s allowed to be built in each one - a single detached house, a duplex, a mid-rise apartment building, a shop, a factory. They also often set rules within those categories: minimum lot sizes, parking requirements, height limits, and how far a building must sit back from the street. None of this is inherently good or bad; zoning exists in some form in almost every city, originally created to separate incompatible uses, like keeping a chemical factory away from a school.

The economic issue arises when zoning becomes highly restrictive specifically about housing. Single-family zoning - rules that permit only one detached house per lot, banning duplexes, triplexes, and apartment buildings outright - covers the majority of residential land in many American cities. When that’s the rule across a wide swath of desirable land, builders are legally barred from adding significantly more housing units even in neighborhoods where demand to live there is extremely high.

Supply elasticity: why some cities respond to demand and others don’t

Economists describe how easily supply can expand to meet rising demand using the idea of supply elasticity. In a market with elastic supply, a surge in demand mostly gets absorbed by new construction, and prices rise only modestly. In a market with inelastic supply - where zoning makes it difficult or illegal to build more - a surge in demand has nowhere to go except into price, because the quantity of housing simply can’t expand to match it.

This is a big part of why two cities with similar job growth and population growth can have wildly different housing costs. A city that allows dense construction near its job centers can add supply as demand rises. A city that restricts most of its land to single-family homes effectively caps supply, so the same rise in demand shows up almost entirely as higher prices rather than more housing.

Two cities, same demand shock

Imagine two similarly sized cities that both add 50,000 new tech jobs in a decade. City A allows apartment buildings near its job centers and, in response, roughly 40,000 new housing units get built over that period. City B restricts almost all of its land to single-family homes, and only 8,000 new units get built in the same period, mostly through slow, difficult approval processes. Both cities experience the same rise in demand, but City B's inelastic supply means nearly all of that demand pressure shows up as sharply rising rents and home prices, while City A absorbs much more of it through new construction.

Exclusionary zoning and who bears the cost

Some zoning restrictions have historically been described as exclusionary zoning - rules that, whatever their stated purpose, function to keep housing scarce and expensive enough to exclude lower-income households from a neighborhood. Because construction costs and zoning rules make it hardest to build the cheapest types of housing, tight zoning tends to raise prices most severely at the lower end of the market, pricing out exactly the households with the least room in their budget to absorb it.

"Rising housing costs are just about population growth"

Population growth and rising demand are real, but they aren't a full explanation on their own, because plenty of fast-growing cities keep housing relatively affordable by allowing supply to expand alongside demand. The sharpest, most persistent housing cost increases tend to show up specifically where demand is rising and zoning simultaneously prevents supply from rising with it. Growth by itself doesn't have to mean unaffordability; growth combined with restrictive zoning reliably does.

Key takeaways
  • Zoning laws legally determine what types of housing can be built on any given parcel of land.
  • Single-family zoning restricts the majority of residential land in many cities to one house per lot.
  • Supply elasticity explains why some cities absorb rising demand through construction while others absorb it almost entirely through price.
  • Restrictive zoning tends to hit the lowest-income households hardest, since it disproportionately limits the cheapest types of housing.
  • Housing costs are shaped by both demand and how easily zoning allows supply to respond to it.
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