July 16, 2010

The challenges of "in-between densities"

Density is a strange word, especially as a description of human settlement. It's a planner's abstraction, a quick way of saying how many houses, apartments, or sometimes people are placed in an area. After decades of Americans seeking out places to live at lower density, we seem to be in a period of reversal, where higher densities are somewhat more popular and definitely promoted as more virtuous.

I don't think, though, that either pole - "low density is good" or "high density is good" - really captures the dynamics of how people actually live in housing of various densities. It's far more complicated than that, which unfortunately will make this post longer than I'd like it to be. That complication, though, is at the heart of a lot of conversation.

At extremely low densities, where a household might have a hundred acres or more, people are isolated. While it's still certainly possible to get into trouble, that vast amount of space provides a buffer between people. Density can increase from there to probably one unit per four or five acres before other people even become visible. Below one dwelling per acre neighbors are generally visible, though interactions with them may still be more optional. The quarter-acre lot was kind of a suburban standard for a while, providing lots of space while bringing neighbors into closer views. Eight dwellings per acre is closer still, smaller, more city like. (I understand that the Fall Creek neighborhood in Ithaca is around seven units per acre.)

Something happens between those densities and the intense density of a big city, though. I quoted Jane Jacobs' Death and Life of Great American Cities earlier about the importance of neighborhoods, but she also has something to say about the transition from lower densities to higher ones that rings true even in the much smaller-scale world along Dryden Road, from Route 13 to Collegetown.

(Anything in square brackets [...] is me commenting.)

We ought to look at densities in much the same way we look at calories and vitamins. Right amounts are right amounts because of how they perform. And what is right differs in specific instances.

Let us begin at the low end of the density scale [not exactly, by Dryden standards, but...] to understand, broadly, why a density that may perform well in one place is poor in another.

Very low densities, six dwellings or fewer to the net acre, can make out well in suburbs. Lots at such densities average, say, 70 by 100 feet or more. Some suburban densities go higher, of course; lots at ten dwellings to the acre average just under, say, 50 by 90 feet, which is a squeeze for suburban living but, with clever site planning, good design and genuine suburban location, can yield a suburb or a reasonable facsimile.

Between ten and twenty dwellings to the acre yields a kind of semisuburb [the Garden City ideal was around 12], consisting either of detached or two-family houses on handkerchief plots, or else of generously sized row houses with relatively generous yards or greens. These arrangements, although they are apt to be dull, can be viable and safe if they are secluded from city life; for example, if they lie toward the outer edges of a big city. They will not generate city liveliness or public life - their populations are too thin - nor will they help maintain city sidewalk safety. But there may be no need for them to do so.

However, densities of this kind ringing a city are a bad long-term bet, destined to become a gray area. As the city continues to grow, the character that makes these semisuburbs attractive and functional is lost. As they are engulfed and embedded deep in a city, they lose, of course, their former geographical closeness to true suburbs or countryside. But more than that, they lose their protection from people who do not "fit in" to each other's private lives economically, and they lose their aloofness from the peculiar problems of city life. Swallowed in a city and its ordinary problems, they possess no city vitality to contend with these problems.

[Discussion of twenty units per acre and above as city densities...]

Unfortunately, however, densities high enough to bring with them innate city problems are not by any means necessarily high enough to do their share in producing city liveliness, safety, convenience, and interest. And so, between the point where semi-suburban character and function are lost, and the point at which lively diversity and public life can arise, lies a range of big-city densities that I shall call "in-between" densities. They are fit neither for suburban life nor for city life. They are fit, generally, for nothing but trouble.

The "in-between" densities extend upward to the point, by definition, at which genuine city life can start flourishing and its constructive forces go to work. This point varies. It varies in different cities, and it varies within the same city depending on how much help the dwellings are getting from other primary uses, and from users attracted to liveliness or uniqueness from outside the district. (209-10)

For successful city life, she sees around 100 units per acre as a key point for vitality, a long way from the 100 acres per unit this story started with.

The part that most interests me here, though, is the notion of "in-between" densities, a range of densities that create problems without creating solutions for them. At low densities - below the roughly 6 dwellings per acre she cites in an age where citizens were perhaps more fond of density - 'city problems' don't really happen. At 10 dwellings per acre, it's more difficult: "clever site planning, good design and genuine suburban location, can yield a suburb or a reasonable facsimile".

Between 10 and 20, new problems emerge:

apt to be dull... will not generate city liveliness or public life... nor will they help maintain city sidewalk safety... a bad long-term bet, destined to become a gray area... lose their protection from people who do not "fit in" to each other's private lives economically, and they lose their aloofness from the peculiar problems of city life.. they possess no city vitality to contend with these problems.

And densities between there and much much denser are "nothing but trouble", unless some other positive features can save them.

When residents worry about increasing density above 8-10 dwellings per acre, it's not just that they know less than the wise planners encouraging density. It's that they can feel the challenges to come.

Posted by simon at July 16, 2010 12:06 PM in
Note on photos


Mark C. said:

I came across this doing some research. Your observations of what causes city liveliness to occur are interesting. There are certainly other thresholds - 7 units per acre to support minimal bus routes and to meet the LEED-Neighborhood Design sustainability crtieria; 15 units per acre to support neighborhood retail, coffeeshops, vibrant parks, as well as more decent bus service, etc.

But I have to disagree with 2 points:

1.) I do not believe the "in between densities" of 10-20 units per acre are undesirable. In fact, I belive they produce one of the most livable city forms, providing row houses with some green space, allowing families to feel comfortable living "in the city" rather than moving to the suburbs. These homes could potentially be affordable as well. If the streets are tree-lined, its particularly pleasant. If rear yards are tight, consider shared internal green courtyards in each block. One of my favorite row house cities is Montreal, but of course they exist throughout the eastern U.S. and in San Francisco. New ones, like Orenco Station in Portland, are being built.

2.) "Urban problems" you mention have generally been found to have little or nothing to do with density, but rather are symptomatic of broken societies, disparities in wealth, education and resources, etc. There are many extremely safe, dense neighborhoods and cities, and many dangerous sprawling suburbs. Some "urban problems" are common in rural areas.

Well, first I'd strongly encourage you to read this in the original - these are not so much my ideas as my agreement with Jane Jacobs' nearly 50-year-old Death and Life of Great American Cities. If you're researching planning, it shouldn't be difficult to track down.

Jacobs wouldn't disagree with you on point 2, the importance of high densities. The chapter this comes from is titled "The Need for Concentration". She looks at these issues from the perspective of Manhattan's densities, and finds them more very workable. I agree that high densities solve at least as as many problems as they create, and that there certainly are dangerous sprawling suburbs.

On point 1, though, I'm quite certain that Jacobs would shake her head and wonder sadly that you'd fallen for the mystique of the Garden City movement she fought so strongly against.

However, context matters most of all. Are those "in-between densities" placed in areas where the surrounding life of the city will help them to thrive? Or are they placed on the edge, where their own development may be slow and their connection to the city tenuous? Are they purely residential, or is there more happening in the neighborhood? What kind of traffic - particularly pedestrian traffic - flows through the neighborhood?

The same questions apply to the LEED density. 7 units/acre on an isolated parcel, even the 15 suggested for more vibrance, just isn't a great idea unless the context fits the development. (100 units/acre wouldn't be smart there either, but developers aren't likely to be _that_ stupid.)

The context I inhabit includes a city of 29,000 in a county of 10,000, spread over 460 square miles of land. It's not exactly Montreal, San Francisco, or even Portland. In this area, I suspect that "in between densities" will fare even worse than Jacobs describes. We don't entirely lack the other positive features that can help, but don't have them in the abundance we'd need to avoid these problems.

(Jacobs mentions North Beach-Telegraph Hill in San Francisco as having density around 100 units per acre. The activity of that dense core could certainly help support lower densities around it.)

Anyway, I definitely encourage you to track this down in the original. I suspect you'll find it at least somewhat compatible with what you're looking for, and the places it disagrees with you might provoke good ideas.