Chicago expanded its accessory dwelling unit (ADU) rules on April 1, 2026. In the first five and a half months under the new regime, the city recorded 495 ADU preapproval applications across 42 of 50 wards, including 215 in April alone. After that initial surge, monthly applications remained above the busiest month recorded in 2025 under the prior program. Of the 495 applications, 446, or 90.1%, were pre-certified.
The data capture an early response to the rule change, not completed housing. Preapproval is an upstream administrative step; applicants must still obtain building permits, construct the units, and ultimately place them in service. The before-and-after comparison therefore establishes a sharp increase in people seeking to exercise the newly available development right, but not how many additional ADUs the reform will ultimately produce.
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If a land-use restriction has been limiting activity, we should expect some response soon after it is lifted. Chicago’s recent ADU application experience suggests that response can appear almost immediately.
Applications are not completed housing, and not every reform will produce the same response. But the speed and volume of new applications are informative. If a rule change removes a material constraint on otherwise viable housing activity, some market response, such as applications, permits, land transactions, or project proposals, should become visible well before new homes are built. Those early indicators can help tell us whether the reform is actually changing behavior.