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
BRANDON DONNELLY 
Dear Brandon,
You may remember us meeting at a Larry Richards convened panel a few years ago.
I have been following your blog with interest for some time now, and have been particularly interested in your recent observations on the subtle relationship of urban density and building height. But in your blog today referring to Paris and Barcelona, you betray, in your conclusion your (developer’s?) bias towards height.
It would be more accurate to conclude that for any given urban density, the most environmentally responsible building height will be the lowest one that still allows for acceptable facing distances .
Thanks for your attention,
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Hi George, nice to hear from you. I was actually trying to be agnostic on height and simply point out that mobility is a key consideration. But one of the challenges in Toronto is that there are relatively few places to build and so, when you can build, I will admit that there is a bias towards height.
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Brandon,
I’m one of your silent followers who appreciates your thoughts on the developing city, but I have to speak up on this one. I agree with you that many in Toronto do not understand that density and building height are related, but that tall buildings are not better density. As someone who lived in London, UK for 8 years, I returned to Toronto in 2016 with a new perspective on this. I look around the city and see so many examples of how the city is getting this wrong.
While London is getting more tall buildings, most of the city is evenly distributed in height. When you get on the Tube and travel around the city, you don’t pop up to find a sudden concentration of towers. It’s about the same everywhere we go. The exceptions to this are places like Canary Wharf (ironically developed by Canadians). As a business core in London, the GLA now has to find ways of getting tons of infrastructure to a concentrated part of the city to support all those people in super high density. The congestion you get in that one part of the city is unlike everything else there (and will lead to higher GHG through inefficiency including in transportation). It looks exactly like what we do here in Toronto.
Toronto continues to cram tall towers into pockets of free land that benefit developers as it maximizes the profit per square meter of land. I don’t think anyone can argue that isn’t why this happens. What I don’t understand is why the city doesn’t shape their planning to encourage even distribution of lower buildings. Concentration of super tall buildings in small pockets creates congestion of people, utilities, shopping, and the issue of transportation. Humber Bay Shore is a perfect example of this as the area is suddenly demanding new transportation, shopping and utilities, while 5 km west down Lakeshore Blvd, the main street struggles and stays at 2-storey. Downtown continues to tower while Bloor Street (as you pointed out across from High Park) continues to stay below 2-3 floors.
While I agree not everything in London is better, I do feel if the City of Toronto spent more time experiencing what their European cousins have been doing all this time, they might wake up to the idea that even distribution of density would benefit the whole instead of current practices that I feel only benefit a few.
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