Streets and the buildings that line them interact, but some interact better than others. Why? Because of the relationship between building height and street width, among other things.
This is a simple idea generally referred to as the “height to width” ratio.
So, if you have a 50 foot wide street lined by buildings that are about 50 feet tall, that’s a 1:1 ratio. But if the the buildings are only 25 feet tall, that’s a 1:2 ratio, because the street is twice as wide as the buildings are tall. There are numerous images on the internet that illustrate this idea, but here’s a good, succinct PDF that sums it up nicely.
So why does this matter?
Generally, getting these ratios right is thought to be a key to creating a strong sense of place. In urban areas, many people like to see at least 1:1 ratios. I’ve found that the places I like the most — Boston, Venice, Paris, villages in the Cinqua Terra, etc. — tend to have even higher ratios, with buildings much taller than the streets are wide.
This makes sense for a lot of reasons, which is probably why people have been building tall(ish) structures along narrow streets for millennia. Economically, for example, it saves on infrastructure costs when you have more people clustered along small streets.
But height to width ratios are also about the feel of a city. As Great Streets San Diego points out in this nice summary, the idea is that they give a necessary sense of enclosure to a street:
A Street requires the same good proportions as any room to make it feel good. It is the “walls” of the street that are key to creating good proportions and a sense of place. The buildings on either side of the street form the walls of the street “room”, and as such are called the “Street Wall”.
That paper goes on to argue that 3:2 and 1:1 ratios create a strong sense of place, while 1:3 ratios and lower offer “no sense of place to the street.” Unsurprisingly, those are the ratios seen in suburban areas.
These ideas are not uncontested, but I think the best argument in their favor comes from the streets themselves. Would you rather walk along a rowhouse street in Boston, or a street lined with strip malls in LA? Would you rather walking along a boulevard in Paris, or University Blvd. in Orem?
And if you think I’m just a biased city-lover, visit Disneyland and walk along Main Street; if my recollection is correct, the ratio there is about 1:1.5 or so. Main Street is an imitation of course, but its designers chose to use that form because it works and because people like it.
In other parts of Disneyland, such as near the Blue Bayou restaurant, ratios are closer to 2:1, which is quite urban. The result is that even though millions of tourist wander through those alleys, they still convey a sense of excitement and discovery.
My point is not that I like Disneyland — I don’t, actually — but just that successful places of all sorts display the same general height to width ratios.
Malls also use this idea; the ratios inside usually range from between 1:1 or 1:1.5 (University Mall in Orem) to 2:1 (City Creek mall in Salt Lake).
Finally, this idea is particularly important for Utah. As everyone knows, most cities in Utah have extremely wide streets, which were a feature of the Mormon grid. But what everyone may not realize is that if the streets get wider, the buildings have to get taller to produce the same effect.
So, in Portland, where streets tend to only be 50 or 60 feet wide, a five or six story building creates a comfortable 1:1 ratio. That gives Portland an exciting and engaging feel without it having to include many massive buildings. The skyline of Portland is even fairly unimpressive, but walking the streets is a pleasure.
But in Salt Lake City, where streets are in some cases twice as wide, buildings have to be closer to 100 feet tall to produce the same effect.
This is a huge problem for Utah cities, and one that is perhaps poorly understood. Tall buildings get more and more expensive the higher they go, for example, and more generally if streets feel inhospitable or lack a sense of enclosure people will avoid them.
The result is that even if Salt Lake managed to become as built up as Portland — something that won’t happen any time soon — it’d still feel much smaller because the height to width ratios would be completely different and more suburban. In fact, you could drop the exact same buildings from any major city onto a Utah street grid and the wider streets would radically alter, and diminish I think, the feel of the environment. (That’s true of any street grid of course — drop Seattle onto New York, Boston onto San Francisco, etc. and they all change — but Utah’s wide streets are an extreme case.)
There are ways to solve, or at least mitigate, this problem, which I’ll discuss in future posts this week. But for now, suffice it to say that this is indeed a problem. If we want our cities along the Wasatch Front to feel inviting and hospitable, we have to think about ratios. In the end, experiencing our cities should feel unique but it shouldn’t feel inferior.