Building height and density are not one and the same. You can have tall buildings configured in a low-density way (think post-war towers in the park). And you can have low/mid-rise buildings configured in a high-density way (think Paris and Barcelona). This is one of the reasons why it is important to decouple density and tallness when thinking about our cities.

This line of thinking is the approach that a recent study took when trying to determine the optimal built form for minimizing climate impact. In the study they define four building typologies: 1) high density, high-rise, 2) low density, high-rise, 3) high density, low-rise, and 4) low density, low-rise.

What they found was that taller environments tend to have higher life cycle GHG emissions, but that lower-density environments are (obviously) far more land consumptive. To determine life cycle GHG emissions they looked at both embodied and operating emissions, which is why the taller stuff didn't score as well under their methodology. There's typically a lot of concrete and steel in tall buildings.

This lead the team to conclude that if you want to optimize around climate impact, you should probably aim for that perfect middle ground: dense, but not super tall.

But as Joe Cortright (City Observatory) rightly pointed out in his email newsletter, one of the big limitations of this analysis is that it does not consider transportation-related impacts. And since we know that transportation is one of if not the largest source of GHG emissions and that how we get around is heavily dependent on land use patterns, it is probably an important piece to consider.

Photo by Alfons Taekema on Unsplash

I was recently having a discussion on Twitter about midrise buildings and architect Dermot Sweeny raised the important distinction between creating "spines" and creating "districts."

What he was referring to with "spines" was the way in which Toronto is intensifying its "Avenues" with midrise buildings. It is a kind of linear form of intensification which almost always means that each building must transition in some way to the low-rise housing that typically abuts our Avenues. This is far less relevant in districts.

We have started to increase housing supply in our "Neighborhoods" through things like laneway houses and garden suites, but in most cases, we are arguably not creating urban districts.

This is of course a touchy subject. But I think it's an important discussion to be having for a number reasons:

• Increasing housing supply is a good thing

• Angular planes and other transition measures make housing more expensive

• Urban places are, I would argue, better defined through districts rather than spines

• Mixed-use (employment) becomes more viable with districts

• Transit infrastructure is better utilized with radial density around its stations

Can you think of any others?

Photo: Old Montrêal (Shot on iPhone)

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