Vancouver seems to have developed its own style of plex, which cannot easily trace its roots back to one of the original Scottish families. The “Vancouver special,” as it is called, is a two-apartment plex with a large setback and a garage or carport on the bottom level. It appears to be formed from the unholy marriage of the San Francisco single-family terrace and the 1950s-1960s Saint-Leonard/LaSalle plex.

I also don’t think Scotland > Boston > Chicago tells the whole story. It accounts well for the “prairie Victorian” style of two-flat or three-flat in Chicago, but many plexes of that size in Chicago–especially in areas contemporary to the “bungalow belts”–have a prairie style that doesn’t resemble anything in Boston. They are flat-roofed with no front stoop (or a small front stoop) and feature large bay or box windows in the front. Once again, porches are in the back. Unlike many Chicago styles, which reproduced themselves over much of the Midwest (Minneapolis, St. Louis, Cleveland, and Milwaukee all have six-flats that look like Chicago’s) this form appears to be unique to Chicago. It is also the only form of Chicago plex found in large numbers in inner Chicago suburbs such as Rosemont, Niles, Summit, and Skokie.

Scotland > Montreal

Scotland > Boston > Chicago

Scotland > Richmond, VA > St. Louis

Chicago, at least the innermost two-thirds of it, is a city of plexes. We call them “x-flats,” where “x” is the number of units in the building. The most common types are the two-flat, the three-flat, the four-flat, and the six-flat. Two-flats and three-flats look like single-family homes, with the apartment entrances (one up, one down, and possibly one in the basement) inside a front door, although their prairie detailing means we get flat roofs rather than pitched ones. Four-flats and six-flats are larger and have a single indoor staircase leading to the apartments, two on each level. A variation of this type of building slices it down the middle to make a two-flat or three-flat.

We don’t have separate entrances, outdoor staircases, or front balconies in Chicago. Instead, we have substantial back porches and front stoops. This makes for interesting differences in the summer street life of the two cities; Chicagoans have back-porch parties instead of hanging out on the balcony. In many neighborhoods, it is not uncommon to see entire families congregating on the front stoops around sunset (the setting sun hitting a row of brick two-flats is one of the most beautiful images I’ve ever seen), drinking beer and watching the children play.

Even some of our more recent constructions resemble those found in Montreal. We have a type of building called a “four-and-one” that appeared around the 1960s, especially near the lake. It’s not a plex (rather, it’s a large, 24-unit building with four floors of apartments and an elevator), but it shares some of the design characteristics of the examples you posted from LaSalle/Saint-Leonard/Chomedey. Namely, four-and-ones share the underground garages, light-colored brick, and California-style architectural details of Montreal postwar plexes. Even more recently, the condos that are going up in most Chicago neighborhoods are drawing on the form of the plex. You can see both three-flat and six-flat styles that resemble their vintage neighbors in most inner Chicago neighborhoods.

In both Montreal and Chicago, the plex is the perfect scale and design for urban life. The balconies and outdoor staircases (or front stoops) create public space, and the scale is dense enough to be lively without being overwhelming (like the grim six-story walk-ups that populate many New York City neighborhoods, or the ten-story faux-Parisian apartment buildings of Buenos Aires).

The plex still appears to be a much more resilient form in Montreal than in any of the American cities where it once proliferated. Chicago’s plex neighborhoods give way to two single-family (but high-density) “bungalow belts” (1920s and 1960s-vintage) and then the low-density forms of the suburbs. But what strikes me about Montreal is the persistence of the plex even in the suburbs. The newer plex forms (condoplexes, mostly) are still being built off the highway in places like Longueuil, Mirabel, and Fabreville.