Calculating the Ecological Footprint of the Built Environment

Researchers across disciplines continue to seek an accurate method for measuring the carbon footprint of buildings.

Today I took the Footprint Calculator quiz. The results were appalling.

Specifically, I visited the Global Footprint Network’s online quiz to determine my ecological footprint (EF), which is the biologically productive area required to support my individual lifestyle. The brief questionnaire determines how many Earths would be necessary if everyone were to adopt my lifestyle. The alarming result: 6.5 Earths.

The quiz also forecasts my personal Overshoot Day, or the date by which I “would have used as much from nature as Earth can renew in an entire year.” In 2017, humanity’s Overshoot Day was Aug. 2. According to my quiz results, mine was Feb. 26. Ouch!

Why is my environmental track record so poor? The calculator asks only a dozen questions, two about food, five concerning housing, and five regarding transportation. Examples include “How often do you eat animal-based products?” and “Do you have electricity in your home?” I anticipated that because I eat meat occasionally, live in a condo that is only moderately well-insulated, and drive 45 miles per week in a vehicle with unremarkable fuel efficiency, my EF would have room for improvement.

The Global Footprint Network’s efforts to provide a relatable measurement for one’s resource consumption is laudable, particularly given the inherent complexities of such calculations. Today, the nonprofit regularly calculates the ecological impact of individuals as well as nations (the United States apparently requires five Earths to maintain the average American lifestyle). What about buildings? Unfortunately, the organization does not publish data on elements other than the world, its countries, and their citizens. Presumably, national data may be interpreted at a state level—perhaps even at a regional scale. But we are currently clueless about the EFs of buildings.

The brilliance of the EF metric is its inherently obvious goal: one Earth, and no more. The approach establishes a clear, memorable benchmark based on directly correlated outcomes. In this sense, it is similar to popular health-related metrics for fitness, such as the need to take at least 10,000 steps a day. Common green building programs do not take this approach. What does LEED Silver really mean, for example? Or meeting seven petals of the Living Building Challenge? How many Earths would buildings constructed to these or other standards require? If the fundamental goal is sustainability for the planet, what is the target that informs us—definitively—that a building is doing its fair share of work towards environmental sustainability?

One impediment is the use of terms and methods that are easily confused. One example is “environmental footprint,” a term that is more or less interchangeable with environmental impact and lacks the specificity of EF. For instance, the Building and Environment Journal article “Environmental Footprint Assessment of Building Structures: A Comparative Study” evaluates life cycle assessment (LCA) approaches, not EFs. A term in U.S. Green Building Council circles is “carbon footprint,” an LCA measurement that is part of conducting a whole building analysis for LEED version 4’s Materials and Resources first credit (MRc1). While carbon footprint is related to—and part of—a biocapacity calculation, it does not tell the whole story. Nor is it commonly used to refer to an actual physical area.

Researchers in Italy and Spain are working on methods for calculating the EFs of buildings. Scientists in the Department of Chemical and Biosystems Sciences at the University of Siena, Italy, published a chapter in The Sustainable City IV entitled “The Ecological Footprint of Building Construction,” which analyzes two types of buildings and their impacts on biocapacity. According to the authors, EF methodology is applicable to buildings because one can track most of a building’s materials and calculate their embodied energy as well as the consumption of construction-related fuels. Furthermore, the total embodied energy in materials “can be converted into the biologically productive area required to absorb carbon dioxide emissions or to produce materials.” A comparison of a detached house and four-story condominium building in Italy reveals that the house requires 39 times the bioproductive area of its site—versus the four-story building, which demands a footprint 59 times greater than its site (EFs of 20,636 square feet and 31,053 square feet, respectively). On a per capita basis, however, the story changes. A house has an average of 5.2 occupants, each requiring 0.122 global hectares (gha) equivalent EF; whereas a four-story building’s 10.4 inhabitants only need 0.091 gha per capita.

Scientists at the Department of Building Construction at the University of Seville, in Spain, have published their own study of local buildings. Also based on the Global Footprint Network’s approach, “The Ecological Footprint of Dwelling Construction in Spain” attempts to establish accurate calculations for a comprehensive set of factors including construction machinery, construction laborers’ food consumption, water consumption, municipal solid waste, and demolition waste. The study projects the average EFs of multistory residences in Spain by number of floors above ground level. For example, the EF per person for a one-story building is 10.8 gha, versus 4.2 gha for a resident of a 10-story building. Interestingly, the sweet spot appears to be around four stories, with a result of 4.1 gha per resident. Does this finding suggest that the ideal building height, from an environmental standpoint, is similar to a pre-20th-century walk-up apartment?

Such insights point to the future debates and controversies that will inevitably accompany a significant adoption of EF calculations for buildings. Zoning laws could be questioned for their environmentally inappropriate floor area ratio and height restrictions, for example. Housing developers might feel public pressure to conform to specific population density targets, while builders of single-family suburban homes would bear the brunt of environmentalists’ scorn. Any metric that indicates a rationing of material and energy resources will most certainly arouse the ire of political conservatives. Yet targets are fundamentally necessary as an accurate reference for human development—something we currently lack.

I tried the footprint calculator again, this time modifying my answers to see how low my EF could be. I decided to remain in my condo but make significant home improvements to reflect “efficiency-centered design with passive heating/cooling, advanced temperature control and ventilation” and “low electricity use.” I decided to forego all meat and any food grown beyond a 200-mile radius. I also decided to eliminate all automobile and airplane travel, using public transportation exclusively for my commute. How did I do? I now only consume 2.5 Earths, and my overshoot day is May 24. Seriously? What will it take to reach one Earth living?

I am tempted to question such punitive results—something audiences will likely do as EF methodology becomes more widespread. Questions aside, this simple tool reveals a marvelous capacity: the ability for users to make adjustments—and receive instant, quantifiable feedback—to reach a crucial goal. Architects lack this capability entirely for the buildings they design. Considering the massive impact of the built environment, however, such a methodology is necessary to achieve one-world sustainability.

Blaine BrownellArchitect Magazine

(*) Blaine Brownell, AIA, is an architect and materials researcher. The author of the three Transmaterial books (2006, 2008, 2010), he is the director of graduate studies in the school of architecture at the University of Minnesota.