I'm new to the term "ADU", but if you're referring to coach houses those are some of the most desirable apartments in the city, and you can't build more of them

I'm new to the term "ADU", but if you're referring to coach houses those are some of the most desirable apartments in the city, and you can't build more of them. The most egregious zoning ordinance in Chicago is that in many residential districts an existing structure cannot be subdivided into multiple units, but multiple units can be combined into a larger unit. This is a legal bias in favor of rising prices and falling access.