My bad habit is looking at pictures of beautiful streets. I can stare at them for hours in a state of total wonderment. Because they feel comfortable, safe, welcoming, alive… and nobody seems to know why.
But recently, I began to notice a pattern; the best streets all fit the same basic form with regard to width and height (width between -and height of- building facades).
The best streets are about 20 feet wide, and the enclosing buildings are between 1.5 and 2.5 stories in height. Full Stop. No ratios.
If these rules are deviated from, keep in mind:
- Streets narrow than 20 feet usually maintain the human-scale naturally; streets wider than 20 feet must have plenty of people and plenty of trees.
- Buildings above 2.5 stories don’t seem to have any adverse effects besides blocking sunlight; buildings below 1.5 stories pose a serious threat to the comfort and livability of the street.
- Never ever go below 1 story (i.e. setback or parking lot). None of these Great Streets have parking lots, empty fields, or other forms of “missing teeth”.
But we often see references to a “width:height ratio”. Let us examine some contemporary thinking and literature, and see how they went wrong.
J. Speck says:
“…the comfortable walk has to do with the fact that all animals seek, simultaneously, prospect and refuge. We want to be able to see our predators, but we also want to feel that our flanks are covered. And so we’re drawn to places that have good edges, and if you don’t supply the edges, people won’t want to be there. What’s the proper ratio of height to width? Is it one to one? Three to one? If you get beyond one to six, you’re not very comfortable anymore. You don’t feel enclosed.”
This concept of prospect and refuge is quite powerful. But where does this “one to six” come from?
“The threshold when pedestrians first perceive enclosure is a 1:4 ratio of building height to thoroughfare width—typical of low-density environments. In denser urban contexts, height-to-width ratios between 1:3 and 1:2 create an appropriate enclosure on a thoroughfare (Figure 4.2). Highly walkable thoroughfares do not require tall buildings.”
~Designing Walkable Urban Thoroughfares (henceforth DWUT)
According to DWUT, people don’t even begin to feel a sense of enclosure until the height exceeds 1/4 of the width. But is a ratio the correct metric? The illustration referenced by DWUT gives the lie to this concept (illustration source: Community, Design + Architecture):
“Human scale ratios fall between 1:3 and 1:2 as measured from the building fronts.” ~DWUT
A couple stark realities confront me when I look at these two cross-sections:
- The wider+taller cross-section doesn’t look remotely like any of the Great Streets from the Lewis and Boxall photo collections. My personal experience too includes quite a number of wonderful streets, and I don’t recall any of them looking like this.
- The narrower+shorter cross-section has two sides, and the left side looks obviously more comfortable than the right side!
- Both cross-sections are so wide that they don’t feel like a single street; the buildings on the far side of the street make no contribution to one’s sense of refuge. They actually feel like independent “half streets”:
“Street trees may be used to provide a similar sense of definition and enclosure in contexts with lower height and less dense buildings.” ~DWUT
The four “half streets” are defined not by two building facades, but by one building facade and one row of trees.
Viewed, this way, we can easily see that all four sections have basically the same width. Their width is the same not in the sense of a ratio, but in an absolute sense. It is about 15-20 feet.