Monday, July 11, 2011

A Tale of Two Densities

Apartments, Rowhouses and the Spatial Logic of Narrow Streets

In Hoboken, New Jersey, the fourth densest incorporated place in the United States, there is a two-block stretch between 6th and 7th Streets where the "hypertrophic" fabric of the great majority of the city, consisting of walk-up apartments and large brownstones on wide streets, abruptly gives way to a series of smaller rowhouses on narrow streets cut through a single larger block.

The five-story brick apartments lining the block to the right are the so-called tenements of the type which Jacob Riis wrote about and which menaced the Little House in the animated Disney film of the same name.  They are emblematic of New York's urban growth in the 19th century and are still abundant throughout the city. Occasionally mixed among them, up large and ornate stairways, are brownstone townhouses with garden apartments.

To the left, the standard Hoboken city block has been subdivided into three smaller blocks by use of two narrow streets along which, with no setback, are built a series of modest two- and three-story rowhouses more typical of Philadelphia or Baltimore than the New York area.  The apartments across the street tower over these small houses, certainly giving the visual impression of much greater population density:

The stark juxtaposition of these characteristic urban forms virtually begs a comparison of the densities in play here.  Since population figures aren't available, I use the objective substitute of bedrooms instead, counting northwards from where the rowhouses begin:

Rowhouses: 2.5 blocks of 32 rowhouses each = 80 total units
80 x 3 bedrooms apiece = 240 bedrooms

Apartments: 17 apartments (10 and 8 unit) + 13 brownstones (2 unit) = 182 units
182 units x (169 1br + 13 4 br) = 221 bedrooms

So, despite the height advantage of the apartments, the rowhouses actually contain a slightly greater number of bedrooms, due mainly to 1) the spatial efficiencies of having multiple bedrooms per unit, compared to one bedroom units, and 2) the narrow streets, which by subdividing the block more than double the number of street-fronting rowhouses which can be accommodated in the same space.  Adding street frontage has the potential to add both value and density to the land, but is dependent on the use of narrow streets lest the benefits be canceled out by the loss of space to new rights-of-way.

Consider also that while 3 bedroom units are capable of hosting both families and individuals (as roommates), the typical American family will find it intolerable to live in a studio or one bedroom apartment as their immigrant forebears did, no matter what urban amenities are nearby.  Given that family households, averaging 3.2 persons each, continue to outnumber non-family households more than 2-1 in the United States, the rowhouses are better suited to contemporary American demographics and living preferences. 

One option for the apartments, rather than building higher, would be to simply combine one-bedroom units on each floor to create larger 2 or 3 bedroom units (resulting in a decrease in the number of units, but an increase in the number of bedrooms*).  An older New York Times article describes this process, the economics indicating a severe mismatch between supply and demand for larger apartments in New York:
"A two-bedroom apartment priced at $450,000, when added to a one-bedroom apartment priced at $250,000, could easily be appraised as a new four-bedroom apartment worth $1 million, a relatively painless way to increase value by almost half.
Broker after broker offers stories of combinations that typically increased value by 30 percent to 50 percent, relating the details as if they were prospectors in a new gold rush. In one instance, a mortgage broker says, a client put together five studios at a cost of $1.1 million that when renovated were appraised for $2.7 million."
The pattern seems to hold true in Hoboken, as well, given that a renovated rowhouse on the block pictured recently sold for $727,000,  far above Hoboken's mean of $417,000. 

As for overall population density, a neighborhood built of such rowhouses could potentially exceed 50,000 people per square mile, assuming one person per bedroom.  This is a density comparable to Paris and higher than Brooklyn or the Bronx.  If higher densities are possible, they may not necessarily be desirable for various reasons relating to infrastructure, transportation and overall crowding.  All this is not to advocate for a particular type of urban form, though, but as one more way to think about the issue of street width, building height and density.

*This has implications for the usefulness of the "units/acre" metric for density, which will tend to reward neighborhoods of one-bedroom units while penalizing those with more multi-bedroom units.

Related Posts:
Glazer v. Glaeser on Density
Skyscrapers, Height and Density
Can New York Build Its Way Up To Affordability?
More On Density


  1. By the way, a "tenement" is another word for an apartment. There is no difference between a "tenement" and an apartment. In Scotland, the source of the term, the word "tenement" is used to describe an apartment of any price and level of luxury. In the U.S., the word "tenement" is a derogatory term applied to apartments in which poor people live. Thus, when people complain about "tenements," in effect they are complaining about poverty. For example, people say that "I don't want to live in a tenement" means that they don't want to live in an apartment with poor people. Give them a floor-through penthouse on the Upper East Side, however, and they might just be happy.

  2. In San Francisco there is actually a legal distinction between tenements and apartments: apartments have their own bathrooms but tenements have shared bathrooms. (And flats are like apartments but have their own separate entrance from the street instead of a shared hallway.) I don't know whether this distinction is applied everywhere though.

    The census population counts for these blocks don't make any sense. The larger block has 309 residents, which seems believable, but the smaller three are said to have 0, 5, and 114, which is a hard distribution to believe.

  3. Eric -- the Census numbers do not seem credible, I agree. Not sure how to account for that.

    As far as "tenement," I was using it in the derogatory sense applied to the walk-up, shared-bathroom apartments of late 19th century American cities, although the buildings shown have long since been retrofitted with modern plumbing and separate baths. But tenements they were, when built.

  4. The one-bedroom vs. three-bedroom issue can just as well be argued the other way, once you account for the fact that a couple will usually share a bedroom. Where housing prices are high, the comfortable limit for a household with n members is n-1 rooms, not n. A one-bedroom can hold a DINK couple; a three-bedroom will hold a four-person middle-class family, not a six-person family.

    Also, re: Paris, Brooklyn, and the Bronx, you should never compare densities on a single block with densities in a region, which contains parkland, unpopulated hills, and commercial or industrial areas. One is net residential density, the other is overall density. It's how Manhattan has 25,000 people per km^2 while the bulk of its residential areas are at or above 40,000.

  5. Alon, good point on the household v. bedroom issue. The trend does run counter for one-person households, who will tend to double and triple up when prices are high, but it does seem doubtful that would outweigh the trends in the other direction. With 60% of households either one or two person, that's a large market for one bedrooms and studios.

    On the other hand, a market with few 3 br's essentially excludes families (the 40 percent with 3 or more persons, and we may assume that many of the 3s are soon planning for a 4th or 5th). My underlying thought was that overcorrecting for larger households would be an inducement to families while not excluding singles, a situation preferable to a glut of small 1 brs).

    As far as density -- I ought to have made it clear, but I adjusted the density I initially came up with (roughly 75k/sq. mi.) downwards by a third to reflect the factors you mentioned. That assumes a city of mainly narrow streets, though, rather than Hoboken's broader thoroughfares.

  6. Charlie: you're right, apartments with 3+ bedrooms are essential for families. The issue, I suspect, is one of efficiency from the developer's perspective: a 3-bedroom has perhaps twice the area of a 1-bedroom, but the users (3-4-person families) do not have twice the purchasing power of the users of the 1-bedroom (DINKs, singles). It's essentially the same reason why all new construction in New York is luxury and usually high-rise: the land prices are such that you're only going to sell to the rich, so you might as well accessorize for the rich.

    As a corollary, it means the main problem is not zoning - New York could relatively painlessly upgrade each zoning district to the next category over, i.e. R7 (3.43 FAR) to R8 (6), R8 to R9 (7.5), etc. - but the onerous permit process. An "adding floors to existing buildings is free" rule would go a long way toward making it easier for small developers to add density by turning 20 5-story buildings into 7-story buildings rather than requiring large developers to turn two such buildings into 25-story towers.

    As for density: do you mean the net residential density is 75,000/mi^2 including the streets, or excluding? The 40,000/km^2 number I quoted above includes streets - it's the number of people living in a mid-rise residential block divided by the area of the block from street midline to street midline (i.e. 900*260 ft. on the West Side, rather than 800*200).

  7. Rather than a Dickens allusion, this reminds me of a song by Genesis, "Get'em Out By Friday", where Peter Gabriel sings:

    I hear the director of genetic control,
    Has been buying all the properties that have recently been sold,
    It's said now that people will be shorter in height,
    They can fit twice as many on the same building site.

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