The important caveat
Strong evidenceA reform can promise density and still bury it under tiny maps, parking ratios, setbacks, fees, hearings, and delay. Good reform makes ordinary projects legal, feasible, and predictable.
Figures from the papers
The strongest post-reform increases appear after roughly five years, especially for large upzonings.
| Years relative to upzoning | All upzonings | Large upzonings | Small upzonings |
|---|---|---|---|
| −4 | -1 | -2 | 0 |
| −3 | 0 | -1 | 0 |
| −2 | -1 | 0 | -1 |
| −1 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 |
| +1 | 0 | 1 | 0 |
| +2 | 1 | 2 | 1 |
| +3 | 2 | 4 | 1 |
| +4 | 3 | 6 | 2 |
| +5 | 5 | 9 | 3 |
| +6 | 6 | 11 | 4 |
| +7 | 7 | 13 | 5 |
| +8 | 8 | 15 | 5 |
| +9 | 9 | 16 | 6 |
The estimated effects become positive after the reform for both attached and detached homes.
| Years relative to reform | All dwellings | Attached | Detached |
|---|---|---|---|
| −4 | -0.05 | 0 | -0.02 |
| −3 | 0 | -0.02 | 0 |
| −2 | 0.02 | 0 | 0 |
| −1 | 0 | 0 | 0 |
| 0 | 0.1 | 0.05 | 0.04 |
| +1 | 0.25 | 0.15 | 0.1 |
| +2 | 0.45 | 0.3 | 0.15 |
| +3 | 0.75 | 0.55 | 0.2 |
| +4 | 1.15 | 0.85 | 0.28 |
| +5 | 1.45 | 1.05 | 0.35 |
The two groups track similarly before reform and separate gradually afterward.
| Years relative to reform | Less restrictive reform | More restrictive reform |
|---|---|---|
| −5 | 100 | 100 |
| −4 | 100.2 | 100.2 |
| −3 | 100.5 | 100.5 |
| −2 | 100.8 | 100.8 |
| −1 | 101.1 | 101.1 |
| 0 | 101.4 | 101.4 |
| +1 | 102 | 101.8 |
| +2 | 102.8 | 102.3 |
| +3 | 103.6 | 102.9 |
| +4 | 104.7 | 103.5 |
| +5 | 105.6 | 104 |
| +6 | 106.6 | 104.5 |
| +7 | 107.6 | 105 |
| +8 | 108 | 105.4 |
Chicago's cumulative permit paths changed unevenly across neighborhoods and rule types.
| Reform exposure | Affected parcels | Comparison parcels |
|---|---|---|
| Density increase | 410 | 460 |
| Parking reform | 720 | 690 |
| Both changes | 560 | 520 |
Evidence stack
Narrow transit-area upzonings raised affected property values but did not produce detectable additional housing during the five-year study window.
Keep in mind: A localized reform and limited horizon may behave differently from broad reform.
Study details →Transit-supportive zoning helped create development opportunities, but market demand, parcel conditions, public investment, and political support determined whether projects followed.
Keep in mind: Six station-area case studies reveal implementation mechanisms but do not identify an average causal effect of zoning.
Study details →ADU production depended on a bundle of usable zoning, flexible occupancy and parking rules, manageable fees, financing, and technical help.
Portland issued nearly 2,000 ADU permits after 2010
Keep in mind: The study is descriptive: policy, demand, and homeowner selection changed together, so the permit count is not a causal estimate.
Study details →The bonus program enabled small multifamily-style infill, but utility costs, financing, geography, and implementation capacity constrained early delivery.
40% of proposed bonus ADUs were in Moderate Resource areas, versus 25% of all ADUs
Keep in mind: Most observations were proposed or permitted rather than completed; overlapping state and local reforms prevent a citywide causal conclusion.
Study details →Substantial upzonings increased housing over five to ten years, especially where prior zoning was binding and rents signaled strong demand.
About 9% more living space and housing units in upzoned areas after five to ten years
Keep in mind: Local quality-adjusted rents did not differ significantly from later-upzoned controls; effects may diffuse across the wider market, and the setting is one Swiss canton.
Study details →A broad reform covering roughly three quarters of residential land produced a large increase in permitted homes relative to non-upzoned areas.
21,808 additional permitted homes over five years
Keep in mind: Permits are not the same as completed or net new occupied homes.
Study details →Loosening reforms were followed by modest average supply gains, while tightening reforms reduced middle-income-affordable units and raised rents.
Loosening was associated with 0.8% more housing after 3–9 years
Keep in mind: Reforms are heterogeneous and the cross-city design remains observational.
Study details →From evidence to policy