At CarbonPositive ’19, Architects Single Out a Culprit: Big Buildings


For the offices of First Tech Federal Credit Union in Hillsboro, Oregon, Hacker Architects used ample cross-laminated timber, a material that sequesters carbon and is increasingly used in Pacific Northwest construction. Courtesy Jeremy Bittermann

Are big buildings the enemy? This wasn’t exactly the question posed by last week’s CarbonPositive’19 in Chicago, hosted by Architecture2030 and Architect magazine, but it might well have been, given a few of the somewhat startling statistics introduced there. More than one speaker at the two-day event—which gathered architecture and engineering CEOs, along with a hotel conference room full of practicing architects and sustainability experts—referenced Bucky Fuller’s classic query, “How much does your building weigh?”

And for good reason: Environmentally speaking, big buildings—though they range, we might single out business-district office towers—are a big problem. According to Edward Mazria, the organizer of the event and its chief cheerleader, all the steel, concrete, and aluminum that go into constructing big buildings account for almost half of the embodied carbon emissions in the built environment.

What does that mean in practical terms? There are two ways of measuring emissions in buildings: operational carbon (the emissions produced to run buildings) and embodied carbon (those produced to construct them). This breakdown contains a sliver of good news and a load of bad.

Let’s start with the good news. Thanks to programs like LEED and the Living Building Challenge, the building sector has in the past 14 years become more energy efficient. According to the U.S. Energy Information Administration, we’ve more or less flatlined our energy consumption, while significantly adding structures to the total building stock. But of course that in no way offsets the carbon emission increases elsewhere in the sector (and the world). A flatline performance for energy consumption constitutes real progress, but doesn’t even begin to get us to our goal of a carbon-free built environment.

The embodied carbon emissions story is more complicated, as many speakers pointed out. This measure is essentially the carbon footprint for the construction sector—and it’s a heavy one. Those three offending materials are the prime ingredients for most of our buildings, especially large ones. So, if we’ve begun accurately measuring the embodied carbon emissions of our buildings, as it seems we have, then we may need to phase out entirely the term “green skyscraper,” since the carbon emissions required to build them outstrip the operational efficiencies on the performance side. You can add all of the energy saving bells and whistles onto, say, an 80-story office tower—those moves will make the structure more efficient than other behemoths of the same size—but they can’t solve the embodied carbon emissions problem baked into the tower’s concrete slabs and steel structure.

As it turns out, these buildings aren’t a whole lot better on the performance side either. “In most cities, the building sector is responsible for 50% to 80% of total city emissions,” Mazria says, “so relatively few big buildings—1% to 4% of the total number of buildings—are responsible for 25% to 40% of a city’s total emissions.” They’re the architectural and planning equivalent of gas-guzzling cars, the SUVs of the built environment.

The event involved the expertise of many architects, including Stephanie Carlisle, a principal of KieranTimberlake. The firm’s Philadelphia office has been made into an “incubator” or laboratory testing sustainable strategies, including natural ventilation. Christopher Leaman

And yet that doesn’t mean we can’t begin to account for carbon emissions on a project-by-project basis. Stephanie Carlisle, a principal of the Philadelphia firm KieranTimberlake, runs carbon assessments for every building prior to design, using a Revit-based program (Tally) developed by her firm. “I think it’s time for us to own more of our emissions,” she said. This means accounting not just for the energy performance of the building, but the environmental impact of its construction. However, that’s an exceedingly deep and uncharted rabbithole. Most manufacturers haven’t really begun the hard work of measuring the embodied carbon emissions of their products. There is, for example, just one Environmental Product Declaration (EPD) for embodied carbon emissions, for the entire wood industry. A product grown, milled and shipped in a multitude of ways, by a myriad of manufacturers, has one emission impact assessment.

This is a huge missed opportunity for the wood industry, says Brad Benke of McLennan Design, given the increasing interest in mass-timber high- and mid-rise buildings. Cost and supply chains also remain ongoing issues. Still, mass-timber construction is a viable solution for mid-rise buildings, depending on how the wood is milled, and where it’s transported from. In fact, all things being relatively equal: timber trucked from the Canadian Rockies is still more sustainable than steel shipped from China (where more than half of the world’s supply is now produced).

How heavy is your building, indeed?

The summit, a meeting of longtime allies in the green building movement—what Mazria calls “the high ambition coalition”—is a precursor to a much larger meeting in Los Angeles, in March, when Mazria plans to announce newly aggressive climate and emissions targets for the built environment. “We’re in a full-blown climate emergency,” Mazria says. We have to do this quickly. We have about ten years to get this right.”

You may also enjoy “Why the Building Sector May Be Humanity’s Best Hope for Averting Catastrophic Climate Change.

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