8 Density interactions and the density threshold
Buildings can get higher. But land devoted to cars spreads outward and consumes more and more land, gobbling up its available percentage points, as density gets higher — except in the rare cases where garages can be built, which is feasible only with the highest densities and the highest land values.
Usable space, gardens, and courtyards are strongly affected by the height of the buildings that surround them. Except in very hot climates, where small outdoor spaces can be made cool and therefore pleasant, outdoor spaces need to be surprisingly large in order to be really pleasant and genuinely alive.
So space is at a premium. Each of the four colors needs to be bigger, to deal with needs and pressures. Ideally, then, one might hope the density could be reduced. But in fact, in most urban areas, density is typically increasing, thus making it more and more difficult to reach a balanced state where the four colors are in effective functional harmony.
The success and humanity of such an urban environment is extremely sensitive to small changes in density. For example, in the situation described 2,400 dwellings of the size stated can be made to work very well. However, 2,700 dwellings (an increase of only 12%) create dramatic reductions in pedestrian space, the social glue which binds the neighborhood. The reason is simple. Building footprint goes up. Car footprint goes up. The green space, too, probably needs to keep pace with the building area, to keep up with more buildings. If anything, for higher buildings garden space needs to be bigger, not smaller. If green space is increased, too, the result is that pedestrian space gets sacrificed, and ends up far less able to carry the burden, and less able to perform the functions that public space and paths ought to perform.
Because of this interaction among the four percentages, a density of 16 dwellings (or units) per acre is roughly the upper limit of what can be achieved while keeping the environment humane.
#book/The Nature of Order/3 A Vision of a Living World/9 The reconstruction of an urban neighborhood#