I'm confused by your last point. Are we to assume that people living in denser constructions would otherwise have lived in grass huts? Or, less ridiculously, only pre-existing buildings? I would imagine that the alternative between people living in new apartments in a dense area would be sprawl, where they would instead live in new houses, which are going to (per person) have much higher amounts of concrete and steel used.
As an “urbanist”, the kind of “dense urban construction” I would like to see is (some proportion of the) suburbs currently full of single family detached homes on large lots replaced by 3–6 story timber-framed apartment buildings / condos near transit and zoned to allow ground-floor retail. Ideally with narrower roads, fewer parking lots, more public green space, and more land outside of cities left as forest.
Many of the densest neighborhoods in the world have no buildings taller than 5 or 6 stories.
But I would be surprised if a 40-story apartment building and the infrastructure to service it required more concrete than housing the same number of people in a low-density suburb. Consider all of the sidewalks, sewers, parking lots, concrete foundations, elevated highways, bridges, .... involved in building and servicing a low-density car-commuter neighborhood.
The “one plus five” buildings you’re talking about typically have concrete first floors.[1]
You make good points about sidewalks etc. but at the same time that stuff needs to be built bigger and stronger and renewed more in dense urban areas. All I’m arguing for is let’s run the numbers. Don’t just assume city living is more ecological because it’s denser.
The technology now exists to construct buildings in excess of 80 meters entirely out of wood.
With that in mind, it's now possible to construct dense urban areas without relying on carbon-emitting concrete or steel going into the structure. Only wood, which is a carbon sink and can be sourced sustainably.
Given that this is fairly well-known - and that the impact of concrete on the environment well-studied - what is it that leads you to think that the numbers have not in fact been run?
I would not say any of that is fairly well known. Nor that it’s clear whether you’re claiming the general consensus urbanist vision is all wood, or that it’s concrete but the emissions are ok because they’ve been “well-studied”.
I'm imagining that there's an element of truth to what you say - but one would guess that the slabs for these houses are still made up of concrete, not to mention the driveways (as well as all the other infrastructure running to said houses - sidewalks, curbs, etc). Apartments being smaller, I would be surprised if there's a huge difference in materials and construction energy input per capita between apartment living and house living. The economies of scale of an apartment building are pretty big; for example, it has one roof and one slab (obviously way bigger).
It's of course possible to construct all sorts of weird versions of this comparison (tiny houses vs McMansions, ultra-modern mid-rises made from timber, etc. etc).
I suspect it's all moot given that transport is such a substantial component of energy use and these houses/apartments should last a long time.
Lower/moderate density could still mean apartments, just constructed without much concrete or steel. You don’t necessarily neeed concrete slabs with smaller buildings. Transportation could be solar powered. It’s at least plausible that moderate density villages networked by sustainable transport could be more ecological than high density concrete/steel structures.
All I’m saying is I don’t hear urbanists talking about the carbon footprint of construction. It’s like an article of faith that high density is ecological.
you're not including all of the concrete to pave the roads, sidewalks, etc to get to that sprawl. Nor all the plastic and sh*t used on siding suburban houses. Nor all the malls and other sprawl buildings which are also, by code, required to use steel studs and similar construction to dense urban environments. Nor all of the gas / carbon involved in all of the in-efficient travel in those locations.
Eg just becuase it's short doesn't mean it's efficient, and tall doesn't mean inefficient.
What it means is we're all just arguing based on no data and instead preferences.
All good points, but none of us are arguing for doing things they way they’re done now. My question is what we should be aiming for. Is it greener to build max density, given the strength required for those buildings (as well as the transport of food, water and resources into cities)? Or is it greener to build moderate density towns that can be constructed from greener materials and co-located with food and water sources? (Not necessarily single family homes and suburban sprawl.)
I would think the goal is to provide the most efficient building in the places people are providing needed social and economic value. Not to force people into the most efficient space possible. So you're going to have different answers where different climates, industries, and needs are present.
Hyper density isn't going to work in rural/farm/resource areas where people essentially need to spread out. Nor does super low density work where everyone essentially comes together to do things.
In the end I think you need to assume that all of the arrangements exist for a point on the multi-variate optimization curve, and just figure out commonalities that make them all more efficient overall, instead of re-aligning all living on a current single local optima.
