Efficient by what metric? By energy usage, sure, but the one metric that seems to override all others in the US is capex, not opex considerations (which over the long haul can overshadow initial capex acquisition costs).

The rule of thumb I've heard about construction is stick-built SFR is considered relatively baseline cost. Multi-Family Residential (MFR) with a few stories that requires some more robust structural elements is about 2X SFR per square foot. Mid- to high-rises are about 2X MFR (4X SFR) and up per square foot.

Economically living in high-rises is a non-starter in most of the US for many working-class and middle-class families, and you won't see Krugman's touted beneficial effects unless that middle of the population bell curve is in high-rises. I advocate dense urban development, but I have yet to figure out how it can be economically implemented without compromising quality of life, especially with the multi-decade long asset inflation we're experiencing in real estate that is ongoing.

We tried this - most urban centers in America are designed around elevators (and little else), and they've largely been failures that have been defined by blight, decay, and crime.

"Just build tall buildings" is a necessary but insufficient condition for an effective city. Manhattan works not just because it builds up (in fact many parts of it are limited to 6-story buildings) but because it has mastered the complexities of creating livable, workable spaces.

The other downtowns across America saw Manhattan, and took only "build tall buildings" away as a lesson, and they are for the most part deserted, ill-occupied spaces. Simple density and height is not the most important factor - it's not even among the top-10. "Manhattanization" became a dirty word across the country not because Manhattan is bad, but because so many places copied it thoughtlessly and incompetently.

A study of what makes New York City tick that examines Midtown over long-standing neighborhoods like Greenwich Village, the Upper West Side, and even more outlying ones like Harlem and Washington Heights, is doomed to fail, because you're seeing a complex, functional city and the only lesson you're seemingly taking away is "density = good", despite nearly every other urban center in the US being evidence otherwise.

tl;dr: Density is a necessary component of a functional city, but you don't need Midtown Manhattan-level density, and having density is not enough. High-density failed urban spaces are a dime a dozen.

[edit] Side note: elevators aren't actually very efficient at high density. They are great for low-mid buildings because they add a lot of floor area and don't occupy much space themselves.

For very tall skyscrapers it inverts - the number of elevators needed to properly serve the building starts increasing dramatically, eating up valuable floor space. There is a level at which you lose overall floor space for each floor you add to the building.

Some of the supertall skyscrapers currently in existence/being built are in fact taller than they economically should be - and this is subsidized by pride, ego, government, rich benefactors, or some combination of the above.

Tall skyscrapers make all kinds of optimizations to minimize this - destination-based elevators (where you punch in your destination before getting in) are popular, as are express elevators segmenting certain floors, but all of these grant modest gains in elevator capacity at best, and in modern times skyscraper heights are limited not by materials or architectural engineering but by this function of elevators vs. floor space.

It doesn't help that most cities outside Manhattan have parking requirements and often quite high ones, to the point where the parking for an office building takes up as much floor space as the offices themselves. And since elevators can't really transport cars very efficiently, your 100 story building will need to be surrounded by 10 10-story parking garages (or, more typically, you'll have a 30 story building with lots of surface parking around). If you factor in all the surface parking, you don't end up with very much density in the end.

> "If you factor in all the surface parking, you don't end up with very much density in the end."

More important than the reduction in density (which IMO for the most is not actually particularly bad), is the disruption in the street graph that parking lots represent.

Parking lots are awful places that are psychologically destructive on top of being literally hazardous to pedestrians. A parking lot is a good way to make sure you remove any trace of pedestrian travel in the area, and they represent black holes in the street.

One thing I alluded to in the earlier post is that graph connectivity is tremendously more important than density. If the street graph is disconnected (or just too difficult or hazardous to traverse), people will stop doing so, and there goes your urban life.

Small American towns (that resisted the suburban blight of the 50s) have very low density but manage to be extremely livable and functional by virtue of being well connected. Density is truly a red herring - livable, walkable spaces can be created at most densities short of completely rural.

Some New Urbanist developments have moved towards a model where the buildings directly face the street with parking lot "courtyards" in the middle - this model works. It's still heavily dependent on car culture, which is unfortunate, but is tremendous more functional than the suburban American status quo that is the opposite arrangement, where parking lots face streets and there might as well be a cavernous canyon between the sidewalk and the building (if there even is a sidewalk).

Absolutely. One thing that I've noticed personally (and that studies confirm) is that the distance I am willing to walk depends a great deal on what walking is like: whether it's interesting, safe, etc. Parking lots are thus a double whammy, because the both push actual destinations apart, and reduce the distance that people are willing to walk. And if nobody's walking anywhere anyway, why bother building tall buildings in expensive city centers instead of cheaper ones in suburban office parks?

Since you mention New Urbanism, have you heard of the Old Urbanist movement? New Urbanism is an attempt to return to 19th century American patterns, while the Old Urbanists advocate going back to an even older pattern of low-rise and mid-rise buildings on really narrow streets, which is a pattern that has worked well for millenia, and indeed still works well in places like Japan. The narrower streets mean there can be more of them for the same usage of land area, which can mean a much better connected network at a pedestrian scale.

Hopefully skyscrapers will build more inter-building bridges in the future. I wonder if the confluence of telecommuting, robotic goods delivery, and the penchant for urban living might mitigate the skyscrapers' elevator-to-floor optimization challenge by shifting the utilization pattern to one that sees more inter-floor and inter-building travel instead of ground-to-floor travel. There has to be some fascinating data collected by the elevator companies on the statistics of elevator service (mass, destinations, etc.).

> the number of elevators needed to properly serve the building starts increasing dramatically, eating up valuable floor space.

I assume that assumes that every time I take the elevator I am going take the trip to the ground floor to exit the building. But work and stores and cinemas could be on floor 40 of an 80-story building meaning the average distance traveled in elevator would be shorter than if I need to get out to the street every time.

> ... are in fact taller than they economically should be

No doubt there is an optimum height somewhere there. And it's not only about building up, but building closer in general. When people work and live closer together there is less need for transportation overall.

Is there really no reason not to grow foods - is this a researched opinion of yours or just conjecture? The last article posted on HN about the trend of rendering skyscraper designs with greenery noted many of the problems with actually building them (irrigation, water proofing, the ability to support the extra weight of the soil/plants, sunlight/shadows, high winds, etc), I would imagine the problem being even greater if you had to grow edible foods rather than just a green plant.

Well yes I may be wrong on that, maybe its best to grow the greens outside Manhattan. It is a technical issue which should be explored if it seems economically feasible. But surely it's a good idea to grow something on the roof which grows there, I read it also helps insulate the building requiring less AC.