KWCIMBY, or Kowloon Walled City in My Backyard, is a refrain used by some YIMBYs to make it clear that we favor high density and not the missing middle self-compromise. This is not about the literal KWC, which was poor and hideously overcrowded – the floor area ratio from photos looks like it averaged around 8 counting open space, so the density meant it had maybe 6.5 square meters of built-up space per capita. Rather, it’s about the concept of going as high as possible, using higher floor area ratios (the Upper East and West Sides of New York have 12 residential FAR on the avenues) and generous first-world urban living arrangements to create high urban density. This post is about how it might look.
One possible built form is this:
This is 100*100 meter blocks, with 20-meter wide streets; this is not intended to be a city for cars, but at high residential density it’s useful to widen the streets somewhat to provide ample walking and cycling space and to allow very tall buildings while keeping the building height-to-street width ratio reasonable. The buildings are in dark gray, in euroblock form with the courtyards denoted in green.
Internal building layout
The building is 20-meter thick, which is wider than normal for Berlin euroblocks but compensates by not having internal wings, so that the apartments’ area-to-window frontage ratio is about 9 meters, which figure exists in Berlin and Paris. The inner corners feature elevator lobbies, depicted as 10*10 meters, but they can safely be made smaller. Let’s Go LA’s post about high-rise floorplates in Los Angeles, Seattle, and Vancouver shows some examples of elevator lobbies with scissor stairs and some extra corridor space at 63 m^2, and here scissor stairs aren’t needed for fire safety because each of the corners is redundant with the other three.
The footprint of the built-up area is 4,800 m^2. Of that, 722 are circulation space, or 15%; this is not amazing, and it’s possible to do better by having somewhat narrower corridors than 2 meters and somewhat smaller elevator lobbies, reaching about 90% efficiency instead of 85%. If the lobbies remain 10*10, they may include additional functions, such as trash rooms with chutes, or maybe laundry rooms in cities where it’s not normal for people to own washing machines.
The apartment floor plates are forced to be rectangular and not terribly interesting, with rooms opening to windows. My presumption is that each window space is 2.5 meters wide, so a bedroom or an office occupies one window, a living room one to two windows, and unusually large bedroom two. Kitchens can take a full window or be in an open plan with the living room. Bathrooms don’t normally get window space, and the depth of the apartment is such that every bedroom can have an attached bathroom.
An austere apartment is around one window per person, or around 22.5 m^2 per person; a spacious one is around two per person if it’s a family, or 45 m^2 per person, or even three for a single person who wants a guestroom. 45 is normal by Northern European standards and if anything on the low side by American ones, but it’s in practice degressive in household size and American NIMBYism is such that families rarely live in big cities, a household in which half the people are children and therefore do not work not really being able to compete for scarce urban land with a household in which all members work. If there’s abundant space, then middle-class families will take 8-window, 180 m^2 apartments in such buildings, and working-class ones will take 4-window apartments.
So what’s the density?
The courtyard is fully enclosed, so the limit to how much sunlight the bottom apartments get is the ratio of the building’s height to the courtyard width, which is 40 m. In Berlin and Paris one finds many euroblocks with wings such that the ratio of the height to the courtyard width is around 1.8, and a fair number in the 2-2.5 range. Our building can have 25-30 floors, or a height of 75-90 meters, while respecting this ratio. This is a building height-to-street width ratio of about 4, which is not common in Paris and Berlin (I see a bunch of 2 but not 4), but does exist in central residential areas in Tokyo and I think also Taipei, and in commercial ones in New York and London.
25 floors times a little more than 4,000 net m^2 per floor is 102,000 net m^2. If it’s 30 floors, make it 122,000. Figure exactly 45 net m^2 per person, with the more austere floor plans canceling out with vacant apartments, with empty nester apartments, and with three-window, 67.5 m^2 singles. This is 2,265 people per hectare at 25 floors, or 2,718 at 30 floors. Per km^2, this is 226,500, or 271,800 at 30 floors.
The vast majority of built-up space is residential, but with buildings this tall, the ground floor is presumably retail. One trick that can be done is to have retail, such as a supermarket, occupy the entire 80*80 block not including the street, and then put the courtyard on the roof of the supermarket, allowing one or two more residential floors.
A percentage of the buildings is entirely non-residential, such as schools, hospitals, office buildings, and emergency services. Schools are, in British standards, 5.13 m^2/primary student (p. 9), 7.81 m^2/secondary student (p. 10), and 9.28 m^2/16+ student (p. 11), all assuming maximum school size. Schools can be bigger than the maximum assumed in the UK – New York’s Specialized High Schools are each around 1,000 students per grade, and Singapore’s secondary schools and junior colleges have around 700-800 per grade. A 12-story euroblock will fit 6 grades generously at 1,000 students per grade, which is compatible with a base population of around 80,000 at equilibrium, so a square kilometer with 200,000 people needs 2.5 primary and 2.5 secondary schools, or 5 out of 100 blocks used for non-residential purposes. This is the biggest nonresidential, noncommercial use, I believe – everything else is probably 1 building out of 100 each, and maybe a handful of blocks can be parks, with a total of 10 blocks in 100 neither residential nor commercial.
Instead of euroblocks, it’s possible to use building forms without internal courtyards. For example, one can break each 100*100 block into 50*50 blocks, still with 20 m street width, giving 30*30 buildings:
Instead of 4,800 m^2 of built-up area per hectare one gets 3,600, but the floor plate efficiency, again stolen from the standards in the Let’s Go LA post (this time, with scissor stairs), is more than 90%, and the building sizes are completely standard for high-rises in Tel Aviv or Vancouver. With no internal courtyards, one can get 30 floors or so, which at 45 m^2/person is 222,900 people/residential km^2, or maybe a little less because of ground floor retail.
There’s also the modernist form of linear buildings, typical of communist-era blocks in Eastern Europe, and some postwar public housing projects in the Western Bloc, especially France (but the United States preferred cruciform buildings).
The street width in the direction parallel to the building widens, which in cities that retrofit such forms can be seen as generous setbacks, allowing the same amount of light to reach the lower floors with taller buildings. The overall built up area is 3,200 m^2 per floor, of which 2,864 is net. If we keep to a 4-to-1 height-to-street width ratio we can reach 40 floors now, which is 254,600 people per residential km^2.
The streets in this case can be set up to create long parallel blocks, or to do the opposite, alternating the orientation of the buildings to break the wind. And of course, all building forms can be mixed, so one block is a euroblock, the next is four 30*30 buildings, the one after is two linear blocks, and perhaps the one next to that is two 30*30s and a linear block.
Where is this appropriate?
Construction costs for buildings are not entirely linear in building height. The reason one would build 30-story buildings one after the other rather than single-story houses is that the area has high demand. So your town of 200,000 people has no chance of fitting in one km^2 with such buildings – nobody needs such a built form, even if there are no cars, because if there are no cars then every street is automatically a bike lane and then the town’s range is maybe 10 kilometers and it doesn’t really need multistory apartments except maybe right near the center.
So this is a way of organizing large cities. The use of buildings that are not just tall but also big reinforces the size of the city as well – a city of 100 buildings is a city with severe monopoly problems among developers and landlords, whereas one with 5,000 is one where people are upset at large developers but there is meaningful competition for tenants. Cities that are large but not hug would presumably use the 30*30 building form in preference to the euroblock just because it can be done by smaller developers.
In practice, it’s also a way of organizing large, growing cities, or cities that will grow if development is liberalized. One doesn’t easily replace heterogeneous blocks with big buildings without a lot of demand. Tel Aviv and Vancouver have 30*30 skyscrapers because they are medium-size, high-demand cities, so any site near city center with a few small buildings can be redeveloped; of note, neither uses this building form much outside city center, except perhaps at transit-oriented development sites around designated town centers like Metrotown.
So the isotropic picture at the beginning of the post is an abstraction. In practice, there are always gradients in density, and that’s fine. Some areas get 40-story buildings, other gets smaller ones, or no redevelopment at all; that’s why, even in environments with liberalized zoning like Tokyo and Seoul, neighborhood-scale zones do not reach 200,000/km^2 at developed-world crowding levels. KWC was a unique situation, a tiny no man’s land, and even though Hong Kong is the developed world’s overcrowding capital and has tall buildings to boot, its built-up density has not recurred.
That said, KWCIMBY building forms remain valuable for urban design. City centers genuinely need more development, and while the very center of the city should mostly have offices, one doesn’t need to go too far to get to areas that are mostly residential and mostly very desirable. Tall, densely spaced buildings reaching 200,000 people/km^2 would facilitate comfortable living in the post-car city, and it’s useful to plan for them in the near future.