Single Stair Reform in Chicago
Removing a second stairway and the corridor connecting it can recover ~10–25% more livable space per floor. Chicago's building code currently requires two stairs in most residential buildings over a certain height. Single stair reform would let builders use that space for actual housing. Cities like Seattle and New York have already adopted this change. The zoning map and floor plan tool below show where this matters most in Chicago.
This map highlights the parts of Chicago where single stair reform would have the biggest impact. These are zoning districts that allow enough housing density that a second stairway wastes significant total space.
The two color groups show fully residential zones (green), which allow housing on every floor, and ground-floor commercial zones (blue), which require a business at street level with housing above.
The numbers (7, 10, 15) are density caps, labeled "du/sl" (dwelling units per standard lot). A standard lot in Chicago is 25 x 125 ft, or 3,125 sq ft. Larger lots allow proportionally more units. The higher the density cap, the more units in the building, and the more total space lost to a second stairway.
Every lot in Chicago has a zoning code like RM-5 or B3-3. The code controls how many units can be built and how big the building can be. For example, RM-5 requires 400 sq ft of lot area per unit, so a standard lot fits about 7. RM-6 requires 300 sq ft per unit, so a standard lot fits about 10.