Zoning Supply Elasticity: The Math of Missing Middle Housing
Upzoning is not a silver bullet, but it is mathematically necessary to arrest rent growth in high-demand metro areas. Our analysis of localized supply elasticity data reveals stark differences in how markets respond to regulatory relief.
The Elasticity Chasm
In evaluating housing markets, we look at the elasticity of housing supply—the percentage change in housing stock resulting from a 1% increase in price. Academic consensus (e.g., Saiz, 2010; Glaeser & Gyourko, 2018) demonstrates that physical geography and regulatory environment dictate this elasticity.
| Metro Area | Estimated Supply Elasticity | Regulatory Restrictiveness (Wharton Index) |
|---|---|---|
| San Francisco, CA | -0.4 (Highly Inelastic) | 1.94 (High) |
| New York, NY | -0.5 (Inelastic) | 1.82 (High) |
| Chicago, IL | -0.8 (Moderate) | 0.12 (Low) |
| Houston, TX | -1.2 (Elastic) | -1.41 (Very Low) |
Translating Upzoning into Units
When a city legalizes "missing middle" housing (duplexes, triplexes, ADUs) by right, it effectively flattens the supply curve. However, the short-term impact is constrained by construction capacity and financing costs.
Take a hypothetical 5% expansion in allowable density in San Francisco. Due to its highly inelastic nature (bound by geography and remaining subjective review processes), our models indicate this translates to only a 2% reduction in median price growth over a 5-year period compared to the baseline. In Houston, a similar regulatory easing yields a 6% price reduction effect.
The "Filtering" Effect Takes Time
Critics of market-rate construction argue that luxury apartments do not help lower-income renters. While it is true that new construction is largely priced at a premium, the arithmetic of "filtering" is robust over the medium term. When a higher-income household moves into a new unit, they vacate an older unit, which absorbs demand that would otherwise bid up the prices of C-class workforce housing.
According to a 2023 working paper by Evan Mast (W.E. Upjohn Institute), 100 new market-rate units create approximately 70 units of vacancy in lower-income neighborhoods within five years, purely through migration chains.
Common Mistakes in Analysis
Mistake: Treating "Upzoning" as Immediate Construction
Legalizing missing middle housing expands the capacity for housing, but does not guarantee it. Financial conditions (interest rates), construction labor shortages, and remaining discretionary review boards (design review) act as severe bottlenecks.
Mistake: Ignoring Filtering Timelines
Expecting market-rate construction to immediately lower rents for bottom-quintile earners is mathematically unsound. The "filtering" effect—where new luxury builds create vacancy chains—typically takes 3 to 5 years to materialize in lower-income neighborhood data.
Frequently Asked Questions
Run the Zoning Impact Model
Model the impact of by-right zoning expansion on median housing prices across different metropolitan statistical areas.
Launch Housing ModelCommon Mistakes in Analysis
Mistake: Treating "Upzoning" as Immediate Construction
Legalizing missing middle housing expands the capacity for housing, but does not guarantee it. Financial conditions (interest rates), construction labor shortages, and remaining discretionary review boards (design review) act as severe bottlenecks.
Mistake: Ignoring Filtering Timelines
Expecting market-rate construction to immediately lower rents for bottom-quintile earners is mathematically unsound. The "filtering" effect—where new luxury builds create vacancy chains—typically takes 3 to 5 years to materialize in lower-income neighborhood data.