Reading Alon Levy's recent post on transit and employment centralization started me thinking about the urban consumption of space, at home and at work. Does an office district, during working hours, contain an even denser concentration of people than its tall buildings might outwardly suggest? And what implications might this have for commutes, and for proximity of homes to workplaces?
Census figures tell us that Manhattan, which Alon discusses, has 2.30 million jobs and 1.59 million residents. What we want to know here, however, is how much space each person occupies, on average, both at home and at work. This requires determining the total amount of residential and non-residential square footage in Manhattan.
For commercial space, the task is easy, as the New York Property Tax Report catalogs it by gross square footage, showing a total of 591.6 million square feet of office and other non- residential space. Residential property poses more of a challenge, since the Report only lists the number of housing units, rather than the total square footage of residential space. What we do know, from 2010 Census Data, ACS information and real estate records, is 1) the total number of housing units in Manhattan; 2) the distribution of these housing units among studios, 1 BRs, 2BRs, etc., and 3) the average square footage of each type of unit sold over the past several years.
In combination, these three factors permit a rough estimate of the total square footage of residential space on Manhattan: 975.3 million square feet (representing the average apartment of 1151 square feet multiplied by 847,090 total residential units). Adding so-called "non-yield" space – including a building's hallways, lobbies and utility rooms, estimated at between 15 and 30 percent of an apartment building in colder climates – results in a gross residential area of 1.258 billion square feet. To find the square footage per person, all that remains is to adjust for vacant offices and apartments, again using census data:
What significance do these numbers have for the distribution of offices and residences in a city? They do suggest the difficulty of achieving high proportions of commutes by foot or bike in a city dominated by a compact central business district of office towers, as a single tower will require more than triple its total square footage (in fact, more than that, as population figures include non-working age persons) in residential space to achieve a 1:1 match of living to working space on a per person basis. Yet, even in Manhattan, residential space is overwhelmingly mid-rise. The very dense Upper East Side can supply only a fraction of the workers, within walking or biking distance, needed to fill the office buildings of Midtown. At its best, it will be a transit city; far more often, in the United States, it will be a car-dependent city.
As urban living becomes increasingly desirable, however, this balance can shift. Conversions of Class B or C office buildings into condos can swiftly change the resident/employment ratio, as has happened in lower Manhattan. Could the same ever happen in Midtown? A little employment decentralization, after all, might not be such a terrible thing.