Chicago’s Northwest Preservation Ordinance (NPO) aimed to reduce displacement pressures in Logan Square. Some provisions (like tenant-focused rules and demolition-related fees) were contentious, but one section offers a clear, map-friendly idea.

Preponderance of the block limits conversions of multi-unit homes into single-family homes on blocks that are already largely multifamily. Thresholds vary by zoning: RS-3 is mostly single-family, while RT-3.5 allows more small multi-unit buildings (like two-flats). Use the below map to explore where similar rules could help preserve housing options citywide.

See the explainer boxes below for background and a quick “How To” guide for the map. For more detail, read our methodology here.

Preponderance of the Block: Citywide Map (NPO)

    • It restricts deconversions (changing multifamily housing into single-family housing) when a block is already meaningfully multifamily.

    • Under the ordinance as written:

      • In RS-3, deconversion is prevented if more than 50% of the block is already multifamily.

      • In RT-3.5, deconversion is prevented if more than 40% of the block is already multifamily.

    • To help neighborhood organizations evaluate whether a similar policy makes sense given their local housing patterns and “neighborhood character.”

    • Strong Towns Chicago’s broader position is to support multifamily and diverse housing options citywide, not only single-family housing.

  • Use the left-side filters to choose (1) what multifamily-percentage thresholds trigger the rule and (2) which zoning districts the rule applies to, so you can see how different settings would affect different blocks.

    • “More than 50% RS3 or more than 40% RT3.5 (Ordinance As Written)” shows where the ordinance thresholds would apply across the city as originally drafted.

    • Other threshold options let you test stricter or looser rules:

      • More strict (prevents more deconversions): e.g., “more than 10% RS3 or 0% RT3.5” — blocks trigger the restriction more easily, so more deconversions would be blocked.

      • More lenient (prevents fewer deconversions): e.g., “equal to 100% RS3 or 90% RT3.5” — only blocks that are almost entirely multifamily would trigger the restriction.

    • The ordinance as written applies only to RS-3 and RT-3.5 districts.

      • Choose “Only RS-3 and RT3.5 districts (Ordinance As Written)” to mirror the original scope, which would then only show blocks in RS-3 and RT3.5 districts.

    • Do not select this toggle if you want to see how all blocks would be affected, even if a block is not in an RS-3 or RT3.5 district.

For questions about this map, contact Aaron Feldman.