Buildings Must Become the Earth's Sixth Carbon Sink

The Mahonia, a mixed-use building in Eugene, Oregon, designed by Arkin Tilt Architects.


By William Richards

The mission of the AIA’s 2030 Commitment is to empower architecture firms to reduce energy consumption and carbon emissions of buildings in accordance with the 2030 Challenge issued by 2021 AIA Gold Medalist Ed Mazria, FAIA. That has to do with the operational carbon of buildings, or what is emitted during their use, as much as it has to do with the embodied carbon of buildings, or what is emitted during their construction in the manufacturing, transportation, installation, and maintenance phases. As architecture firms adopt the 2030 Commitment—and in light of a renewed international conversation about carbon after COP26 in Glasgow—three architects leading the charge to reduce embodied carbon talk about the challenges of industry adoption and offer messages to building product manufacturers about getting to carbon neutrality faster. Vanessa Hostick, AIA, is a sustainable design leader at HOK’s Kansas City office; Kit Elsworth is a building performance specialist at KieranTimberlake and an instructor at the University of Pennsylvania; and David Arkin, AIA, is co-founder of Berkeley, Calif.–based Arkin Tilt Architects.

William: What defines the terms of the conversation today about carbon from the perspective of the average architect?

Kit Elsworth: As we scale from maybe residential to large commercial, we're needing to rethink more normative practices that would otherwise be overlooked in terms of what materials we're using in our buildings construction and in understanding those profound impacts that they have on the environment. There are bio-base and carbon-sequestrating materials that are, hopefully, coming on the horizon and becoming more mainstream. But until then, our concrete and other building materials [will continue to] have a definitive carbon footprint that’s very hard to eliminate.

David Arkin: The need is “both-and”—both to bring these carbon-storing materials online as fast as possible and also reduce the impacts. We can't just rely on the resources that lock away carbon. We also have to reduce the impacts of the industry.

Vanessa Hostick: It's important to acknowledge that this is new and complicated and very overwhelming to go to a client and present this as a business case. The important part is to pick one area and start understanding and improving because it starts to fall into place. And that was the experience we had when energy modeling came out. It was scary because we didn't know what we were going to find. And you were afraid of being told you did bad, when in reality you had to benchmark and measure so that you could improve. And we had to remove that stigma and that fear that this wasn't about judging you for doing bad. This was about finding where we are so that we can get better.

William: What is the biggest challenge to widespread industry adoption?

Vanessa: I think part of it was benchmarking and calculation, just taking that step to get the numbers on paper so that you could improve, and acknowledging where you were, has been hard.

Kit: Similar to energy modeling, I think a huge hurdle is expertise or training. Some software can seem a little bit intimidating, and if a firm is thinking about doing it internally, [the challenge] is overcoming that technical barrier. The main difference, though, between energy modeling and life cycle analysis [LCA] is from the market's perspective; everything that's covered under a typical scope of LCA is owned by the architect. It's all within our scope and our agency to influence; whereas with energy modeling, you could argue a large part of it is the engineer's domain of mechanical systems. So it’s on us, and it’s within our expertise [as architects] to optimize LCA.

David: I would agree with that and add it's all also about working in collaboration with our structural engineers, who bring a lot of the high carbon materials to the forefront: and it's building codes that are driving some of the need for these stronger materials.

William: What are the dominant—and measurably successful—practices for reducing embodied carbon right now?

David: Build with the materials that store carbon and try to offset the ones that otherwise emit. Petroleum-based foam and aluminum cladding don't take you in the right direction, but straw bale and bamboo and wood do. That part of the equation's simple. There's also understanding what the metrics are and being able to measure it to take that step. For buildings the measure is kilograms of CO2 omitted per square meter, and 400 is about average.

William: How does that play out in terms of operational carbon versus embodied carbon?

David: First, the time value of carbon cannot be ignored. Embodied emissions are immediate and can’t be offset with lower operational carbon savings 15 or 30 years from now. Embodied carbon varies greatly, but unlike operational carbon, it can be reduced or eliminated across all building sizes, types, and heights. So while 400 is about average, 75 can be considered “very good.” It is difficult to get to zero. It is really difficult. We had a carbon-storing goal for a modest residential project in Colorado. We were only able to get to 30 because we had to use carbon-emitting materials such as concrete, mineral wool, and steel instead of other carbon-storing ones where we hit the ground, and the need for durability and high insulation levels at 10,000-foot elevation is significant. Along with Arup and other partners, we developed a four-story mixed-use carbon-storing prototype. It can be done, but it takes some aggressive steps.

William: Vanessa, you mentioned before that benchmarking a calculation is a huge challenge. Working at the scale that you do at HOK, looking at how we measure—whether it's cradle-to-gate, cradle-to-site, cradle-to-grave, and so on—where do we find the strongest argument for how to make a positive impact?

Vanessa: Measuring gets weird fast—I'll admit that—and our running joke in the office is that we're committed to a relentless pursuit of “more sustainable sustainability”—because every time we think we've done a good job, we always find one more thing to improve. When we work on really big buildings, we tend to look at a total carbon and end-of-life for those buildings because we're hoping they’ll be there for 100 years. And at that time scale, it's important to understand what we can sequester in the building, as well as reducing its initials. So we look at both. We actually look at the A1-through-A3, cradle-to-gate, and we look at a total carbon or a total life cycle.

William: Why is that important for a building that will stand for a long time?

Vanessa: In part because we recognize a lot of our finishes and systems will get swapped out two or three times in the lifetime of the building. If we can reduce the number of times they’re removed and give the building a longer life, it really adds value for a lot of the big buildings we do. How do we use less and reuse more? That can be a scary conversation because I'm asking a structural engineer to use less and convince a client it's still safe. Sometimes we ask the question, “Do you really need two of those? Could you just have one?” And that's one of the most successful practices, to just use less and scale it back and then, after that, look for replacement and sequestration strategies so that things you design last longer, which is about regenerative sustainability.

William: Kit, I wondered if I could draw you in on this question, too, about the obvious solution to simply use less of everything. Are there other hidden opportunities that maybe aren't so hidden, or perhaps that are hidden in plain sight, so to speak?

Kit: I would say what comes to mind is the multitude of cascading benefits you get from mass timber. Obviously, there are other things you can do, but in replacing steel for wood, there are many codes around the country that also permit you to use the mass timber structure as an architectural finish. You don't need dry wall. You don't need additional materials that you would otherwise place inside of a building that would then accumulate into a larger body carbon footprint.

David: It’s like the question about getting to zero. How do we get there?

Kit: Yeah, and my mind goes to finishes—finding ways to not add finishes that are purely aesthetic. If you have concrete slabs, use that as your finished floor ceiling, for instance. When I think of getting to zero, I feel that we really have to talk about those bio-based solutions.

David: I like to paraphrase Michael Pollan's food rules, but for buildings—build shelter, not too big, mostly plants—which builds on this conversation of using less. But I want to tack onto that an idea of using the best. And there are a lot of material manufacturers—I'm thinking of gypsum offhand, one of the materials highlighted in the Carbon Smart Materials Palette (—where a company has gone to reduce the carbon footprint of one of their products. We, as architects, need to seek those out. The more we can specify those, the more impetus manufacturers will have to bring these and other carbon-storing alternates online.

William: That brings us to specification—and on this call, you represent different scales of working and of firm sizes. So how do these opportunities map onto the design process? Is the specifier's job to raise possibilities for the design team? Is it the design team's job to make sure that they've got the right people specifying the right products? Is it the firm owner's job to mandate awareness and a set of best practices?

Vanessa: Internally, we try to give as much power to the project architect and the project designer as possible because they're really representing the project and the client's best interests. And sometimes that means taking a counter option back to the client and asking them to do more. We have a fantastic internal resource of a series of senior specification writers internally, but they will tell us it's up to us to get it onto the job. We're the advocates. And I think sometimes we forget, as architects, that we have the power to go to the manufacturer and say, “We need you to test this. We need you to do better.” We don't have to be passive and just accept what they give us. So that's where we try to put the power in the process.

William: I’d say that, beyond architects, product manufacturers are an important audience of this interview. What’s critical for them to know?

Vanessa: Put products and information like Environmental Product Declarations [EPDs] on the website where I can find it, and don't make me call six guys and harass somebody in a factory to get a piece of paper. Make information easy to find.

Kit: We have been looking at ways to use EPDs to create performance spec language. Then we are also notifying suppliers ahead of the time to let them know we are going to be having a performance spec. If you want to play the game, this is what we're looking for. So product manufacturers either need to get their EPD if they don't have one, or they need to identify ways that they can either meet that performance spec language or let us know what it's going to cost to get there—what the “add” is.

William: How has that gone so far?

Kit: We've been successful in that we’re working with our contractors to act as intermediary to reach out to suppliers. For steel and concrete, we realize we have to kick those conversations off super-early in the process, and I highlight steel and concrete because it’s a lot of our projects globally, which is about two-thirds of our embodied carbon footprint. So we're often looking at optimizing those two.

David: One of the questions our structural engineers ask now is, when does the concrete have to go into service? Because if we can extend the drying time, the curing time, we can use a weaker mix, a less carbon-intensive mix going in and just give it a longer time, and reduce the carbon footprint right there. I was thinking when we started this portion of the conversation that there's a huge marketing advantage and edge that can be created for architects who are on top of this. And I know one way that we've been able to succeed is because we attract clients who bring this priority to us—but it's communication that makes sure that the decisions they make down through the process align. Paralleling this, there’s a marketing edge for product manufacturers to bring low-carbon and carbon-storing materials online and to the market. My message to them would be rethink the resources they're working with. If a major insulation product manufacturer developed a straw-based panel, and they could use their size and marketing power to bring that online, that would be a game-changer for a lot of architects who have to constantly specify traditional materials for their projects.

William: At this intersection that you describe between research and practice, what are we doing right to get to 2030’s goals, and what are the things we need to push harder to target buildings a carbon sink?

Kit: My easy response is timber. We got to get steel and concrete out of our buildings as much as we can and replace it with timber or other carbon-sequestering products.

David: You're not going to get there without measuring. Analytics are the big order of the day, and you can use those to your advantage—and that's what we need to do with these materials. For those alternates, you then need to ask, “Is there something better than this alternate?” So instead of steel or concrete, you might say, "Ah, mass timber." But then within mass timber you might say, "Hmm, is there a bamboo-based mass timber product that we might be able to use which is not going to have the impact on our forest, which take 40 years to come to maturity, when we can use bamboo which has a renewable cycle that's one to five years, or straw which has a one-year renewing cycle?"

Vanessa: That’s our relentless pursuit of more sustainable sustainability. When we go into the big sports venues, we talk about, How can we take this giant typically heavy concrete structure and make it a sink? How is this a community asset? I'm not talking anymore about reducing energy and reducing carbon. I'm talking about producing this as a community asset. The question needs to be, “How can I generate so much energy that I'm now covering the neighborhoods next to me so that they don't have to worry about the utility costs and they can just live?” That is the way we go into projects now.

This group interview has been edited for length and clarity. William Richards is a writer and architectural historian based in Washington, D.C., and the author of Bamboo Contemporary: Green Houses Around the Globe (Princeton Architectural Press, 2022).

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Image credits

The Mahonia, a mixed-use building in Eugene, Oregon, designed by Arkin Tilt Architects.

Eric Bischoff