The Goldilocks Zone of Urban Density

 

Why we like big cities with lots of very tall (skyscrapers) office and apartment complexes: Concentrations of jobs and servicing professionals, easier construction of mass transit to reach more people with shorter links, most efficient use of valuable urban-center real estate and easier access to a variety of urban amenities. Why we like suburban housing: space, space, privacy, space, pride of ownership, space, it’s the American dream. Suburban living may require longer commutes and absorb more energy use and water usage, but it is just so American. We know that individual detached housing is the least environmentally friendly urban approach, even as solar panels are helping… a bit. You might think, however, that the skyscraper model would carry environmental benefits to the max. Well, according to new research, that’s not really true.

The world, particularly China and much of modern urban Asia, is obsessed with taking a relatively small parcel of land and accommodating tons of people in that space by building upwards. Minimizing individual environmental footprints, maximizing heating and cooling, and building near jobs, restaurants and retail – often in the same buildings. Not exactly. At least according to a recent statistical study, summarized in a July 5th release (“Decoupling density from tallness in analysing the life cycle greenhouse gas emissions of cities”) in the newly created periodical, NPJ Urban Sustainability, an open access, online-only journal for urban scientists, policy makers and practitioners focused on high-quality research on sustainable urbanization.

Here’s the headline: “There is a growing belief that building taller and denser is better. However, urban environmental design often neglects life cycle GHG emissions [greenhouse gasses]. Here we offer a method that decouples density and tallness in urban environments and allows each to be analysed individually. We test this method on case studies of real neighbourhoods and show that taller urban environments significantly increase life cycle GHG emissions (+154%) and low-density urban environments significantly increase land use (+142%). However, increasing urban density without increasing urban height reduces life cycle GHG emissions while maximising the population capacity. These results contend the claim that building taller is the most efficient way to meet growing demand for urban space and instead show that denser urban environments do not significantly increase life cycle GHG emissions and require less land.”

There is another approach, one that requires more land but still relies on multistory offices and residential buildings, just generally not more than six or seven stories. We know that ultra-tall buildings can block sun and stymie airflow. That’s not the biggest issue. But the lower-rise model, one that has defined Paris for a very, very long time, seems to offer an ability to sustain high-density living with a more environmentally friendly impact. 

Nate Berg, writing for the August 18th FastCompany.com, provides more insight into the above study: “Taking into account the full lifecycle emissions of urban development, the study finds that high-density low-rise cities are more environmentally friendly than high density high-rise cities. (They’re both still better than the suburbs.) Paris, for example, with its mostly five- and six-story buildings, produces fewer overall emissions than both sprawling exurbs and skyscraper cities like Hong Kong. It’s the Goldilocks zone of urban density and height—just enough to get the efficiencies of urban living but not so much that the resulting emissions wipe out the other sustainability benefits.

“‘We’ve always been looking at this problem from a building perspective,’ says Francesco Pomponi, the study’s lead author and a professor at Edinburgh Napier University. ‘If you look at the building perspective and you analyze the footprint, of course a tall building is better. The high-rise building houses more people. But when you start looking at the bigger picture, you realize you cannot put two high-rise buildings as close as you can two low-rise buildings . . . To build tall, you need heavier structures, chunkier foundations and also, for a lot of good reasons like privacy, ventilation, and daylighting, high-rise buildings need to be further apart.’ Given the land required to build tall buildings and the carbon-intense building materials like aluminum and steel it takes to construct them, a neighborhood of skyscrapers would result in about 140% more total emissions than a Paris-like lower-rise area with the same population.

“‘If we need more materials and the buildings need to be further apart, maybe it’s not so straightforward that we need to be packing high-rise buildings together,’ Pomponi says.” We tend to examine the ecological realities of high rise living in an overall abstract analysis after the structures are built. There are very few studies, unlike the above report, that detail the entire impact, including the realities of construction. Time to take the big picture approach to just about everything we do.

I’m Peter Dekom, and to understand humanity’s impact on the earth requires a truly in-depth and total analysis… every time!