[paytonc]

The near northwest side famously has apartments which have many, but tiny, bedrooms. (Good luck finding a vintage studio apartment in Wicker Park!) I'd always heard that attributed to it having been built for large immigrant families back in the day, but that explanation would have applied to Pittsburgh or Boston, too.

Here's a potential culprit that's unique to Chicago: the freestanding building on a 25' x 125' lot. The result is a 20' wide building, with a 5' gangway between buildings. Given a 20' width, you can either fit:
- one 20' wide room, like a nice "front room"
- two rooms side by side, maybe 12' + 8'; without a hallway, one of these can't be a bedroom (e.g., a kitchen)
- two 8.5' rooms on either side of a 3' hallway
Since the bedrooms are often along the "bowling alley" in the middle of the plan, the last situation often applies.

By comparison, DC/Baltimore/Philly rowhouses benefit from being smaller structures. There's no possible way to attempt to squeeze two rooms side by side, so instead the single rooms are wider; since there aren't dark side windows, the houses can only be about two rooms deep. Even if a rowhouse is also 20' wide, there's no way to have the "bowling alley" down the middle because those rooms wouldn't have windows -- unlike Chicago's side-lit bedrooms.

25' lots are also common for New York City tenements, but... there aren't gangways, so the plan can comfortably fit two 11' wide rooms on either side of a 3' hallway.