The Dreaded Density Issue

Having worked in communities big and small across the continent, we’ve had ample opportunity to test ideas and find approaches that work best. Urban design details. Outreach tactics. Implementation tricks. Many of these lessons are transferable, which is why we’ve created “Back of the Envelope,” a weekly feature where we jot ’em down for your consideration.

A number of recent conversations with Stefanos Polyzoides, Howard Blackson, and Matt Lambert regarding density and residential types has me thinking about building typology as one solution to visualizing and embracing density.

The Lincoln Institute has done a good job of making the touchy subject more approachable on their website and the wonderful aerial photography of Alex S. MacLean goes a long way to clarifying the difference between similar densities that ultimately prove more or less desirable in their final built form. For example, compare the similar densities from San Francisco and Boston below. The narrow buildings around Louisburg Square are human scaled and very approachable from the view of the pedestrian. In contrast, the monolithic buildings in San Francisco create a canyon at the street level and contribute very little to the effort to promote sustainable densities.

San Francisco – South Beach neighborhood at 52.5 units per acre: Bing Maps

Boston – Louisburg Square at 52.9 units per acre: Bing Maps

San Francisco – South Beach neighborhood street view: Google Maps

Boston – Louisburg Square street view: Google Maps

Instead of debating the number of units per acres, planners and city staff should consider addressing types of buildings that are permitted within different zoning categories. Not only is this the most understandable approach for the lay person, it’s the most predictable for the builder and the city. This method of addressing density is supported by the latest zoning technologies including the SmartCode and a number of other Form Based Codes, particularly those authored by Moule & Polyzoides Architects & Urbanists. The units per acre on the basic housing types for a mid-size U.S. city are as follows:

Single family house 50’ x 100’ lot

8.5 DUA


Townhouses with 2 car garage

18 DUA


Walk up flats parking 1.5 cars per unit

36 DUA


Andrés Duany makes a good case for considering density at the scale of the neighborhood rather than the individual building. He states that the types listed above, in the context of a neighborhood reflecting the average United States market for need and choice results in roughly thirds: or one acre of apartments per two acres of townhouses per four acres of single family houses. This delivers a net density of 10 units per acre for a complete neighborhood. Next time you’re faced with a frightened crowd of density opponents, try turning the conversation to types of buildings, and allow that discussion to evolve into addressing the neighborhood as a whole, rather than simply a sum of its individual parcels.

–Susan Henderson

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Filed under Back of the Envelope, Planning and Design, Theory and Practice

15 responses to “The Dreaded Density Issue

  1. Love your posts! Great to hear such good sense once in a while.

  2. Reblogged this on Stupidityflowering and commented:
    Refreshing good sense!

  3. Reblogged this on Poetries of Place and commented:
    I’ve always thought density analyses were misguided. “Density” is, to me, cold data. Crowds, however, are people engaged in activity. When I think high density I think skyscrapers. Crowded places are good and pleasnt to be in especially when these places are abuzz with street-level activity. While it’s tough to define a concept like “human-scale architecture,” the contrasting photos between residential areas in San Francisco and Boston illustrate it to a certain extent.

  4. Pingback: Think Building Types, Not Units Per Acre | APA News Feed

  5. THREE WORDS I learned in planning school, that always need to go together, (don’t know the origin of the quote/concept)-
    “Density, Diversity, Design”

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  7. Thanks for the reblogs Steve and brickshire! I agree the activity at the street level makes all the difference, but I’d also make the case that the most active and engaging streets tend to be in the more “human-scaled” environments. Think West Village vs. Midtown Manhattan. And Paul, you summed it up. Diversity and design are the keys to making density desirable.

  8. Pingback: The Dreaded Density Issue | PlaceShakers and NewsMakers | DFW REimagined – The future of real estate

  9. Can you clarify how it comes out to 10 DUA? My math came out to about 15 DUA (using the 8.5/18/36 DUA over 4/2/1 acres). Are you including streets and other non-residential uses when you say “complete neighborhood?” (not trying to be a stickler, just genuinely interested in your method)

  10. Pingback: visualizing density « thedensityproject

  11. Pingback: Residential Density | urbanexus

  12. Hi Scott,

    Yes, I was calculating the neighborhood as a whole, including streets. If you limit it to parches, you will get about 15 DUA.

  13. Pingback: Density can be either “monolithic” or “approachable and humane”, difference is scale «

  14. I have to say that you’ve picked the least typical neighborhood in all of San Francisco! Nice post though, the photos illustrate it well.

  15. Susan,
    Can you show us comparisons at 100+ units per acre?

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