Published on Dec. 2, 2020 by Steven Vance
Updated on Dec. 3, 2020
The Daily Line reported on a new ordinance that the Chicago Department of Housing intends to propose that would ban deconversions on many blocks near the Bloomingdale Trail west of California. A deconversion is the change of a multi-unit house to a single-unit house. It is a practice rampant on the North Side of Chicago, and it has led to the loss of tens of thousands of unsubsidized and relatively affordable housing.
The ordinance is not yet introduced, so I’m making these maps based on what was reported.
As reported by Alex Nitkin, “In single-family zoning districts in the 606 area, the ordinance would only allow the construction of single-family homes on blocks where detached homes make up the majority of buildings”. In other words, the zoning ordinance would set a minimum density for the number of units on a property.
Minimum densities don’t exist in Chicago , but they should, at a minimum, exist around train stations and the bus corridors identified in the zoning code.
The area, shown on the map below, is bounded Armitage, California, North, Kedzie, Hirsch and Kostner. It is approximately 1.4 square miles in area and about 63.4 percent of the zoned land allows only single-unit, detached residences — despite what kind of building is currently there.
The map shows only parcels with multi-family buildings (two-flats and larger). Whichever block has a majority of its parcels shown , then deconversions would not be allowed on that block, and new construction single-unit houses wouldn’t be allowed.
It takes a minute to figure out how to find the blocks that would be protected from having deconversions: There are many supermajority  multi-unit blocks across the area. Check out the northwest corner by Armitage and Kostner, and the 1900 blocks of Kimball and Spaulding; look for several blocks of Karlov west of the north-south railroad tracks.
 Okay, there’s one place where there’s a minimum density: the “Downtown Core” zoning district doesn’t allow single-unit detached houses; the minimum density would be a single-unit above a ground floor commercial space. See 17-4-0207 in the Chicago zoning code.
 I don’t have a quick GIS method to find the blocks where the majority of properties are detached houses, but it’s somewhat simple to find these blocks visually. Additionally, I don’t have a copy of the ordinance so this map may be imprecise.
 I’m also curious how the ordinance will define “majority”. In one part of the Chicago zoning code, a block that’s zoned single-family-only but has 60 percent or more (more than a simple majority) two-flats on the same side of the block will also allow new two-flats.
Chicago prepares a deconversion ban near the 606 [you're reading this one]