Too often, we talk about carbon as if buildings exist in a vacuum. Buildings are part of built and human systems, and emissions are associated with all aspects of those contexts—people and jobs, open space, vehicle miles traveled, adjacency of uses, and infrastructure and utilities.
SOM’s Yasemin Kologlu, Intl. Assoc. AIA, and Ellen Lou, FAIA, are interrogating carbon impacts in the context of building uses, density, transportation, and open space. I talked to them about their research projects—including Urban Sequoia and the in-progress Square Mile Carbon Study—which explore carbon ecosystems.
Kira Gould: Both of these investigations offer new insights on how we think about built form and carbon. Why are you looking at the topic in this way?
Yasemin Kologlu: The built environment is responsible for at least 40% of global carbon emissions. We believe that buildings and cities have the potential to become a solution to the emissions problem, rather than a contributor. The studies we’re talking about today approach this challenge in different ways. Urban Sequoia started with a concept for a single building and a question: How can we reduce the building’s carbon impact, while integrating carbon-absorbing materials? The result is a building design that captures more carbon than it emits. Expanding this approach to a city district, we can make an exponential leap in carbon absorption.
Ellen Lou: The Square Mile Carbon Study examines carbon emissions at a regional scale. We analyzed six different 1-square-mile parcels of land in the San Francisco Bay Area, each representing a typical development pattern—from the high-density, mixed-use downtown core to the single-use suburbs on the periphery. The goal is to understand which development and land-use patterns are most efficient when you take a holistic view of carbon impact per capita, including transportation, embodied carbon, and operational carbon. This perspective allows us to evaluate the trade-offs between different types of development in terms of density, uses, open space, and urban form.
KG: How do single- and mixed-use developments affect our understanding of the carbon calculations of neighborhoods and cities?
YK: As designers, we intuitively understand that mixed-use buildings and districts are more efficient than single-use districts because they create opportunities for different kinds of people and professions to flourish simultaneously. They provide a lifestyle that so many of us who live in cities enjoy—a lifestyle that’s less dependent on cars. And they allow buildings with different uses to share energy and infrastructure, which contributes to carbon efficiency at scale. The Square Mile Carbon Study provides the data to validate this intuition. Taking a holistic view of carbon impact, it shows that every type of mixed-use district—from mid-density to high-density—has a significantly lower carbon impact per capita than a single-use district.
EL: Our study shows, for instance, that the carbon impact per capita of a suburban office-park parcel is almost six times higher than a parcel in the downtown core. Transportation makes up a very large portion of overall carbon emissions, and bringing different programs and businesses together in the same district can reduce the number of trips and time spent in cars, which can have a big environmental impact while also improving quality of life.
YK: There are profound opportunities in using this district approach to right-size our resources and make them as efficient as possible. For example, sharing electricity becomes much more compelling when you have a mix of uses because the peak hours for energy use are different for residential buildings and for commercial buildings.
EL: Here’s a good example: A university campus we’re designing in southern China will require a lot of energy during the academic year. But in the summer, when there are very few people on campus, we can supply that energy to the neighboring community, which will have higher energy needs during that season. So, by taking a district energy approach, both the residential and university facilities can be used more efficiently.
KG: What are the implications for how we think about infill and adapting uses, especially for taking single uses to mixed use, for example?
YK: One of the best ways to reduce whole life carbon is to extend a building’s life span. The longer buildings remain useful, the less embodied carbon we will need to expend in the future to demolish and rebuild them. We designed Urban Sequoia to be transformed over time to accommodate many different uses.
EL: If we combine adaptive reuse with an infill development approach, rather than building on undeveloped land, we can be even more judicious about our collective carbon impact. This approach allows us to tie into existing infrastructures and systems, which opens up all of the opportunities for efficiency that we’ve talked about.
KG: You talk about carbon from a “per capita” and “per job” perspective. Can you explain that thinking and why that is important?
YK: Previous studies have calculated carbon per square kilometer or mile. This doesn’t give a proper representation of our carbon impact because it does not consider the human factor—population density. A dense downtown area would appear as having higher overall carbon emissions per square mile than in a sparsely populated suburban area. But this is misleading: When you divide up the carbon impact per capita, taking into account residents and people who work there, it’s clear that areas with higher population density are significantly more efficient in terms of overall carbon, considering operational, embodied, and transportation-related carbon emissions.
EL: This is true also when you consider single buildings. A high-rise building on its own might have a higher carbon impact than a low-rise structure, and that data is a crucial first step; we’ve actually just launched a service to accurately measure this for our clients. But we need to take this information and apply it further by considering these buildings in terms of efficiency and productivity. We believe that per-person carbon metrics have a lot of potential to shape the way we design buildings in the future.
This article first appeared in the July/August 2023 issue of ARCHITECT.
Read more on building a greener world: Now Is the Time for Radical Collaboration | Can We Halve Carbon in the Built Environment? | The Race to Decarbonize Buildings Is On. | Building on the Best of COP27
Design principal Yasemin Kologlu, Intl. Assoc. AIA, RIBA, LEED BD+C, is a leader in SOM’s efforts to respond to the climate crisis through sustainable design and construction. Her work at SOM–from carbon-sequestering high-rise proposals to the first carbon-neutral district in Paris–exemplifies her forward-thinking approach to design, operating at the intersection of occupant well-being, holistic environmental design, and the latest material and building technologies. She co-founded SOM’s Climate Action Group, which recently announced the firm as a net-zero carbon emissions business through strategic offsets. Beyond her work in the office, Yasemin is the co-chair of AIANY Committee on the Environment and serves on numerous sustainability-focused advisory groups.
Ellen Lou, FAIA, AICP, LEED-AP BD+C, works at the forefront of urban design and planning, advancing new development models and climate-adaptive design strategies to foster healthy, thriving cities for all. As a principal for SOM’s City Design Practice, she brings a global perspective to challenges of urban transformation: integrating priorities for cultural preservation, social equity, ecological resilience, and economic vitality into actionable visions. Ellen’s work has shaped new downtown districts from San Francisco to Shanghai. She was recently elected President of the Institute for Transportation & Development Policy and served on the board for San Francisco Urban Planning and Research.