Thursday, February 17, 2011

Skyscrapers, Height and Density

Going back the issue of skyscrapers, density and residential affordability once more, it seems to me that part of the problem with any discussion about density is a lack of a clear, consistent method by which to measure and understand it.  Population density does not tell us about urban form; units per acre does not disclose the average size of the units, the designed capacity of the units or how much of an area is actually devoted to residential use; and Floor Area Ratio (FAR) is typically only used to measure individual parcels, not whole neighborhoods, and again doesn't tell us much about form (as Andrés Duany has observed). 

The following "density quiz," part of a longer presentation by Redwood City, CA planner Dan Zack, highlights the inadequacy of the units per acre ratio as a measure of density given that the physical form in which similar levels of density are contained can vary widely:
One point which comes across for me in this segment is how building height, although it may be the most immediately noticeable building trait, and the one we instinctively associate with "high density," is far from the only, or even most important, contributor to overall density.  The compounded effect of high lot coverage, modestly-sized units and limited on-site parking can produce exceedingly high densities in the absence of great height, while the Corbusian towers-in-a-park design approach produces much lower density even where buildings are very tall.

The pro-density urban advocate who focuses on the relaxation of height limits to the exclusion of other factors such as parking requirements, mandatory setbacks, minimum street widths and minimum unit sizes addresses only one component of overall density, and one which, from a city-wide perspective, may not have an especially large impact on it. 

Finally, a mindset which holds up the increase of density, by whatever means, as an absolute good, ignores important non-economic costs and benefits of each means of increasing densification.  The negative impacts of very tall buildings on urban life, beyond the obstruction of views and natural light immediately noticed by city residents, have been covered at length by Nikos Salingaros and Léon Krier, among others.  Greater lot coverage and narrower streets, meanwhile, confer numerous benefits, both economic and not, in addition to their positive impact on density.   


  1. This brings up the interesting relationship between density and urbanism. Most assume that high density automatically leads to urban conditions and lack of density precludes it. Those Corbusian towers in a park may still be pretty high in density compared to suburban areas, but they're anti-urban in their lack of diverse street life and requirements for driving everywhere. Conversely, small towns or even farming hamlets that have a very low overall density but compact walkable centers are still quite urban.

    The misunderstandings about density (especially average density) and how they relate to urbanism are also the basis of fraudulent arguments that tout Los Angeles as being more dense than New York City. Los Angeles has denser sprawl, but even higher density areas made up of multi-story apartment buildings are still thoroughly car-dependent and those buildings have plenty of basement parking and no street life.

    As the video illustrates, it's all about how to lie with statistics. The qualitative differences in built form and other regulations have just as much, if not more, to do with the issues as raw density numbers.

  2. Thanks for the comment, Jeffrey. I agree that the potential for mischief with density statistics includes very large (city-wide) scales as well as the very small. In the absence of a clear idea of the form that density takes within smaller more localized areas, those numbers can mislead as much as they illuminate.

    I agree also with your point about urbanism -- if density alone is the goal, good urban qualities will not necessarily result, but if the goal instead is good urbanism (the approach taken by form-based codes), a high density environment will naturally flow from it.