Toronto is known for its tall buildings and its contrasting low-rise neighborhoods. More recently, we have seen a proliferation of mid-rise buildings along the city's "Avenues." This is despite the many challenges and costs associated with this building typology.

But I think it's pretty clear that a further evolution is also underway. Laneway housing, which is now permitted "as-of-right," is in the early stages of being adopted and built out all across the city. And eventually I think we'll see many of Toronto's laneways evolve into fully fledged residential streets; perhaps not all that dissimilar from what you might find in compact cities like Tokyo.

This is very exciting to me and I think of it as the city gaining a third hierarchy of residential streets. We'd have our major arteries and avenues. We'd have our residential side streets. And then we'd have our compact laneways. Dare I say that maybe some of these laneways could even house non-residential uses such as small-scale offices.

But along with this shift, I think it's time we look at another infill opportunity -- something that planners Blair Scorgie and Sean Hertel are calling "density transition zones." What these zones hope to be is a new middle transition zone between low-rise neighborhoods (where laneway suites are already permitted) and mid-rise avenues. A place where "missing middle" type housing might be built in close proximity to major streets and existing transit. Let's call it a 100-200m zone that sits right behind our avenues.

In my mind this is immediately beneficial for two reasons. The first is obvious. It could be a place for frictionless missing middle housing. Housing that's more dense than a single family home + laneway suite, but less dense than a typical mid-rise building.

The second immediate benefit is that this transition zone could be used to help improve the overall feasibility of mid-rise avenue development. The reality is that there are many blocks along Toronto's avenues where the lot depths are simply too shallow for proper mid-rise buildings. Density transition zones could help with this, which would be not that dissimilar from how "Enhancement Zones" were intended to work (they were never approved).

If this were to happen, I think there would also be a strong case for softening some of the "requirements" in the mid-rise design guidelines. Requirements like the 45 degree angular plane that new buildings generally need to conform to. All of this would only help the overall feasibility of more European-scaled developments along Toronto's avenues and, in my opinion, that would be a great thing.

But for the same reasons that Enhancement Zones were highly contentious, I would expect a lot of grouchy people and a lot of pushback on this idea. There will be concerns about encroaching on our single-family neighborhoods, and there will be the usual objections that come up with any new development (density, traffic, dog poo, etc.) But if we're serious about building more missing middle housing, we are going to need to find ways to remove the barriers to entry. This scale of housing is simply too small to support a great deal of friction.

To learn more about how density transition zones might work, I would encourage you to check out the great site that Blair and Sean have put together, over here.

Image: Density Transition Zones