The energetic response by multiple organizations indicates that EC management is not a transient trend but an enduring aspect of design and construction practice. It also suggests that aligning different measurement and reporting systems, assumptions, and responses can create confusion. No single industry standard for EPDs or LCAs has emerged, though the CLF and other professional organizations (including the U.S. Green Building Foundation, AIA, SEI, and Architecture 2030) have formed an Embodied Carbon Harmonization and Optimization (ECHO) Project aimed at clarifying carbon reporting standards and practices. Cropper notes that it is too early for “a consensus yet on what the right tools are for the right project stages, and for the right projects, and for the right design professionals,” though EC3 has enough adherents to be approaching the status of a standard. Though preferences among these instruments vary widely, “the math is very simple,” says Driscoll: “quantity of material times the GWP of the product equals carbon footprint.... It’s actually simpler and more manageable than people think it is.”

As an aphorism attributed to the Nobel Prize-winning cognitive scientist and economist Daniel Kahneman holds, “No one ever made a decision because of a number. They need a story” (Lewis 250). While LCAs provide essential quantitative information, placing it in the context of a persuasive narrative about what a building can accomplish is up to architects and engineers. Though some clients may cite immediate economic justifications for declining to support the work involved in carbon accounting and reduction, the larger story of a built environment transformed from linear and wasteful to circular and sustainable may ultimately be more persuasive. Cropper points out that the multipart mission of SE 2050 calls for not only EC reporting and reduction in projects but communication with architects and “internally educating our engineers and disseminating strategies and knowledge about how to do this, like with our Communities of Practice.”

“The EC3 is basically a database of EPDs,” notes Johnson. “It’s a great idea to help harmonize where information is housed and how it’s collected. In general, though, you have to be aware of what data you’re using: within that tool, you have to have gone through some sort of design. If you just go in there and you want to compare, say, steel to concrete, just looking at the numbers within a tool, you don’t really have a sense of which one could create a lower-embodied-carbon structure, because you haven’t taken it through a design; you’re just comparing EPD values.”

“We always have to be careful to compare apples to apples,” Johnson continues. “For us that means comparing a building with a building, or a system with a system.” Specialists he has worked with find that “all the data points within a building are very difficult. I heard one person say once that there might be up to 2,800 components that could go into a building, and that’s everything: electrical, carpeting, paints, structure, all that sort of stuff. For an architect [who] has to go through and collect all these data points, that’s a really daunting task.... Even within steel, if you just take a wide-flange section and a rebar, you can’t really just compare those EPD values, because the way that those items function within a building is not the same, and the same quantity of material is not used to make it a functional piece of the structure.”

As an example of a comparability challenge, Johnson describes a design that includes a 15-foot column, either a wide-flange section or a hollow structural section (HSS). “Both have equivalent axial capacities; I think it’s around 370 kips. If you multiply through the embodied carbon for the wide-flange column, it comes out to be 440, and if you multiply it out for the HSS section, it’s like 434, very close. But if you look at the EPD values, it’s 1100 versus 1550. So if you just looked at the HSS one, you’d say, ‘Well, this one’s 40 percent higher,’ but if you carry it through a design and get a quantity and a takeoff, they’re pretty much comparable materials at that point.” Comparisons outside the steel domain can become incoherent, he adds: “Steel reports usually in tons within an EPD; wood reports in cubic meters of material. It’s a volume versus a weight, so comparing those is just impossible to do.”

Driscoll cautions that when a design team performs an LCA, gets carbon-reduction figures for specified components, and obtains a LEED credit, that step is not the end of the story. The USGBC does not require firms to demonstrate how much of the materials mentioned in an LCA are actually procured and used onsite, he says, or how designs evolve. “Our role is important: to take the baton and deliver on what that LCA said the project was going to deliver—if not do better, because the LCA doesn’t often get the procurement nailed to the level of accuracy that we’re going to have, because we’re actually buying the material.”

Francesca Meola, principal and senior project engineer at HOK, and her colleague Mark Hendel, engineering practice leader, both emphasize the value of early coordination among members of the full team of design professionals, engineers, sustainability consultants, and contractors. Having worked with steel, concrete, timber, and hybrid structures, they note that the different materials and associated trades have different requirements and that estimates of GWP can inform design decisions at each stage of the process, from initial conceptualization and material choices through schematic design (SD) and detailed design (DD), when architects and engineers still have the bandwidth to make changes to the design ensuring they can achieve their EC goals. “There is a benefit with doing LCA at the very beginning to understand if it would be better to go with a timber construction versus steel versus concrete,” Meola says. “Of course, you don’t have final numbers, but you have an order of magnitude, and you know what would be the best solution in general.” LCA information remains important after a structural material is selected, she adds, informing the details of bay spacing, foundations, floor-to-floor heights, curtain-wall dimensions, and other components. Meola and Hendel allocate EC-reducing decisions to three categories, ranging from low-hanging fruit with no added cost to ambitious maneuvers that can bring dramatic improvements in overall GWP if clients are receptive. “Basket One,” as Hendel terms it, “is stuff that we don’t even want to talk about; we’re doing it, and it’s not going to cost you anything, and you’re going to be happy for it.... It doesn’t even come up; we write them into our spec. The client has no issue with it. The contractor follows the spec. Done.” Examples from Basket One might be choosing steel manufactured with an electric arc furnace (EAF) rather than a blast furnace, or concrete masonry units using recycled glass pozzolan rather than coal fly ash as a cement binder (Meola, Cropper, and Paull all cite Pozzotive, a ground-glass product by Urban Mining Industries of New Rochelle, NY, as an example of an affordable material whose benefits include EC reduction). “You can take a big leap forward just by paying attention,” Hendel says, “just by looking at it and saying, ‘Okay, let’s make sure we’re at least doing the easy ones.’” “When we have our drawings and the specs,” Meola adds, “we do specify the GWP, the content of your target for concrete, for foundations, for steel, and so on. And so, by putting numbers on our drawings and our specs, we are basically saying we want to achieve these GWP contents. And implicitly, you’re saying who can do it and who cannot do it, but that doesn’t have any impact on cost.”

Basket Two comprises green choices with a slight cost premium that might be offset by sacrificing finishes or other details deemed noncritical. On the structural side, material replacements or column-grid adjustments can constitute Basket Two items; “if you want to do really massive spans, then that is going to have an embodied-carbon implication and a tonnage implication,” Hendel says. Basket Three includes “the pie-in-the-sky ideas, and I think the clients are very receptive to those. It’s on us to give them the information to guide them through that decision-making process, and we might be surprised just how far they’re willing to go, especially if it’s a major client.” Major design changes—not revised grid spacing or floor-to-floor heights, but reductions in a tower’s volume or in basement levels—make Basket Three a domain where large pendulum swings of reduced or added cost command high-level attention.

Incorporating EC data into their practice, Meola says, has been straightforward. HOK has chosen OneClick as the firm’s LCA tool; “when we have detailed information,” she says, “we can extract information from our BIM model from Revit and then push it directly into OneClick with minor adjustment. And that’s really helpful to get instantaneous feedback on the quantities and on the GWP for the project, but we use it also without going through Revit, and we have our spreadsheets with our takeoffs, you know, when we’re still in concept.” The output format (including pie charts and other visualizations) is convenient, she says, both at that early stage and when the team has developed a model. Development of an internal HOK system is also in the works, since “we have all these disciplines in-house [and] we are in a good position to get information from the facade team, the architectural team, mechanical, and us... You want to have a tool that clearly shows what are the aspects of the designs that can be changed and have a large impact on the final number.”

It is essential, Meola emphasizes, for everyone on a project to work with the same information. Variability in the quality of EPDs presents complications, since industry-average GWP data and data from individual manufacturers may differ. EPDs for different materials may also use different operational units, and the dates and accuracy of EPD data are not always comparable. (Direct confirmation with manufacturers that figures are current and products are available in the desired quantities, several commentators note, is usually advisable.) “By using OneClick we have access to the industry-average numbers,” she says, “and so when we are then contacted by manufacturers that can provide a lower GWP, we don’t just take it for granted that they can lower the GWP numbers by 50 percent or something like that. But for us, it’s more getting an understanding of what can be achieved out there, instead of using the industry-average numbers, and just knowing that those numbers can be lowered by going with specific manufacturers.”

Distinctions among types of product-specific EPDs are essential. The International Organization for Standardization (ISO) recognizes three types of environmental documentation: Type I (ISO 14024) claims label products that have met requirements set by governmental or professional bodies (e.g., EnergyStar or the Forest Stewardship Council); Type II (ISO 14021) are self-declared by businesses and do not require LCA studies; and Type III (ISO 14025) have been externally verified by a third party performing an in-depth LCA. The exacting Type III EPDs are most accurate and informative.

“We’ve gotten to a point where almost every manufacturer has an EPD, and that gives us the ability to do things that we didn’t have the ability to do 10 years ago,” says Joseph Dardis, P.E., head of presales for construction projects at ArcelorMittal International North America (a Luxembourg-based steel manufacturer). “Seven or eight years ago, we had some industry-wide EPDs; that was a step in the right direction, but that still didn’t really give you the ability to track individual emissions on your specific project.... Now we’ve gotten to the point where almost every manufacturer has their own, and they have it on a facility-specific basis, so you can get much more granular in tracking those emissions. The more specific you can get with a manufacturer and a facility-specific EPD, the better the accuracy of that LCA. And generally when they are a Type III, externally verified EPD, you can have a greater sense of accuracy.”

The system is not perfect, Dardis notes: “There are still dozens of different EPD standards out there, and you can do an EPD accurately according to other standards, and you can have two different results.” Although ArcelorMittal makes its structural steel in Europe, he says, the firm considered it important to publish EPDs to a North American standard for the sake of transparency and comparability to U.S. producers. Databases like EC3 can aggregate data from the wide range of EPDs and inform comparisons; using EC3, he says, “I can search globally for structural steel sections, and I can see 10 different manufacturers and 30 different production facilities, and the embodied carbon of the steel coming from each one of these places. That is a level of granularity that gives me the ability, if I’m a designer, to make very impactful decisions on a project.”

As the field has progressed from industry-wide EPDs to manufacturer-specific EPDs to facility-specific EPDs, Dardis finds that the SE 2050 program is filling in information gaps about emissions for materials in the contexts of project types. “What is the standard,” he asks, “for a healthcare facility, for an office project, for a school? What is the baseline embodied carbon per square foot? If these design firms aren’t compiling this information, we don’t have it, and we don’t know what ‘good’ is and what ‘bad’ is. So I think the SE 2050 program is enabling this to happen.... We manage what we can measure, so if we don’t know what is an acceptable GWP per square foot for an office building, how do we know if we’re better or worse?” It is increasingly possible to say, for example, “Here’s the baseline for a 30-story office building; we did 30 percent better because we have all these tools available to us, and we can show that by procuring specific materials in a certain way, we can address this.”

MATERIAL CHOICES, AFTER AND BEFORE REVOLUTIONS

Reducing EC operates on two basic levels: choosing greener materials and designing structures to use less of them. The material-choice EC reflects the energy used in manufacture, shipping, and construction, with some newer materials offering measurable advantages (e.g., high-strength steels enabling the use of less volume of steel to support equivalent loads). Design strategies, such as optimization to reduce the amount of steel plate, bolts, and welds used, can thus synergize with material choices.

The two major structural materials, steel and concrete, differ drastically in their current and future EC footprints and the questions they pose for design teams at various stages of a project. “Steel is much more mature than concrete when it comes to recycling and CO₂.” comments Paull. Concrete remains more environmentally troublesome, he finds, though he speculates that innovators in that industry are “just on the verge of coming out with some pretty dramatic changes.” Driscoll describes the current condition as asymmetrical: “Steel has been at it for longer, so they’re a little more mature. But there’s more potential right now to decarbonize concrete than there is to decarbonize steel. Concrete is harder to tackle because it’s more regional; steel tends to be more national. For a project in LA, I might get steel from Arkansas. For that same project in LA, I’m not getting concrete from Arkansas.”

Changes in the steel industry over recent decades, Paull comments, are both a case study in technological disruption and an indication of how a sector can progress, though not without costs and casualties. “Up until a couple years ago, nobody was really much concerned about what was going on in embodied material,” he says, but after the transition from basic oxygen furnaces to electric arc furnaces (EAFs) in the 1980s and 1990s, “the two dominant U.S. steel mills lost market share because they didn’t convert fast enough. U.S. Steel is still in business, but with diminished capacity, and Bethlehem Steel no longer exists.” The contemporary industry resulting from this shakeup is a model of circularity by several important metrics: today’s American hot-rolled structural steel is 100 percent recyclable and 93 percent recycled, according to the American Institute of Steel Construction’s figures.

With about 70 percent of all steel produced in the U.S. coming from scrap-fed EAFs, a key determinant of its EC content is the indirect emissions component (Scope 2 in the GHG Protocol’s system), the footprint of the electricity used in the process, which varies widely by region. Where power comes from renewables (wind, solar, and hydroelectric; nuclear is very low in GHG emissions but not considered renewable, since its fuels are mined), the steel’s EC is competitively low. Where power depends on fossil fuels, its EC is correspondingly higher. Steel mills’ locations relative to most job sites make transportation a larger component of the material’s overall EC calculations, though generally not large enough to be the decisive variable. ArcelorMittal’s Dardis notes that “the argument we always get is that as a European manufacturer, what is the effect of bringing structural steel from Europe versus procuring it domestically? What’s the penalty; what’s the tradeoff there? Steel needs to be thought of a little bit differently than regionality. Process and electrical grids are more important. Of course, transportation does matter, but typically, at the end of the day, it’s a pretty small percentage.”

Nucor’s Johnson estimates that transportation costs might typically account for 5 to 10 percent of the steel EC on a project. For practitioners interested in the power sources for particular steel mills, he points to a resource maintained by the EPA, the Emissions and Generation Resource Integrated Database (eGRID) website, which gives data on the power-grid mix for regions of the U.S.: “how many coal-fired plants and renewable sources (being hydro, wind, and solar) that fall within that grid. And then you can utilize that information within that specific mill’s EPD to assess your Scope 2 impacts for the utilization of electricity within that region.” The eGRID data, he says, can lag roughly 18 months behind the present, though regions’ power profiles rarely change dramatically year to year unless major assets like a large wind farm come online or are decommissioned. Examination of power-grid profiles for specific steelmakers adds valuable information to the material’s EPD.