In order to stop climate change, the world needs to reduce the carbon emissions of our buildings. That isn’t up for debate. Reports have repeatedly shown that buildings, or more accurately, the people who use them, account for around 40 percent of the world’s carbon, making it all but impossible to reach our decarbonization goals without lowering their consumption. What still is up for debate is the best way to reduce the emissions associated with our existing building stock.

There are two options when it comes to making an older building more efficient: renovate or demolish and rebuild. The equation is pretty simple: if a new building can reduce its energy consumption enough to save more carbon over its lifetime than an older building, plus the carbon cost of construction, then it can make sense to demolish and rebuild. But as simple as that equation is in theory, it is very hard to calculate in the real world. What makes it so difficult is that we still don’t know exactly how much carbon is associated with every piece of building material and every building process. This is called “Scope 3” emissions, and while we do have ways to estimate it, it is still a bit of a guess. Making the right choice for whether to renovate or redevelop buildings is critical, and most scientists think that we have until around 2050 to decarbonize completely before we have irreversible and possibly catastrophic effects on the planet. However, getting the calculation right means having a better understanding of exactly how much carbon is associated with the construction process.

There are plenty of organizations that have attempted to calculate the sources of a building’s carbon footprint over its lifespan. The World Green Building Council estimates that of the 38 percent of the world’s carbon that buildings emit, 28 percent comes from operational emissions, 28 and 11 percent comes from its materials and construction. By that calculation, roughly 60 percent of a building’s emissions come from its operations and 40 from construction. There are other studies that estimate those numbers to be more like 80/20. If that is true, then you could certainly see why tearing a building down would be the best option, especially if a building outlives its estimated life of 50 years (which it almost always does).

But as hard as these studies try to make sure their calculations are as accurate as possible, the known unknowns have to cast some doubt on their viability. One of the biggest blind spots is how much carbon is associated with each building material. Some products do have what is called an Environmental Product Declaration, or EPD, that independently verifies the environmental impact of each product, but many still don’t. When it comes to more complicated products like fixtures or mechanical equipment, understanding exactly how much carbon they embody requires untangling the complicated web of the global supply chain. “We have a global market; we need international policy,” said Patrick O’Shei, Director of Market Development for NYSERDA, New York State’s Energy Research and Development Authority. NYSERDA was created by the State of New York to “reduce greenhouse gas emissions, accelerate economic growth, and improve the quality of life for all New Yorkers equitably.”

There is also a concern that some agencies, particularly governmental ones, might have an incentive to unfairly scrub their products clean. “Most of our concrete is locally sourced, but more than half the steel comes from China, and sometimes it is hard to trust their reporting,” said O’Shei. NYSERDA has worked hard to find places where building owners and developers in New York can find the most sustainable, often local resources, going as far as to find ways for materials to be brought into some areas like Manhattan by barge, a much less carbon-intensive transportation method than trucks.

It isn’t just governments that are suspect when it comes to accurate carbon accounting; certain large companies have plenty of reasons not to account for all of the emissions associated with their product. “There is pushback from certain industries,” said Ladan Ghobad, principal at ENERlite Consulting, a sustainability consulting firm that performs embodied carbon analysis for buildings. Tracking and reporting carbon emissions is not a priority for manufacturers such as concrete companies. Concrete has a significant carbon footprint, for about 8 percent of the global emission. “There are some new technologies that can lower the carbon created by the cement production process, but regulation and legislation are needed to push toward technological changes,” Ghobad said. She admitted that forcing large multinational companies with lots of lobbying power to change the way they do business will likely get pushback. She suggests inviting those companies to the table for discussion about improvement and legislative changes. This is what happened in California through continuous advocacy from AIA California. As of August 2023, California is the first state in the nation to adopt general code requirements for reducing embodied carbon in the built environment. As much as Ghobad would like to see buildings be built with less carbon, she also worries that too much change, too quickly, could spike the already spiraling costs of construction, “It is already expensive to build, so I personally don’t want to see too many added costs, especially for what it would do for affordable housing,” she said.

As critical as it is to get the rebuild versus renovate decision right, not having a perfect carbon accounting mechanism shouldn’t stop our efforts to understand the carbon associated with our buildings. Carbon Title is a company that is attempting to do just that; they have created a public database of the carbon footprint of every building in the country. I talked to the company’s founders, Trevor Dryer and Miles Haladay, who had a rather pragmatic approach to this problem. “If we try to track everything down to Scope 3 emissions, then no one will be able to report accurately,” said Dryer. Rather than start at Scope 3 for their database, they did their best to estimate both embodied and operational carbon based on local area averages. The software that they use can look at the size, structure, and usage of a building and estimate the carbon that would be needed to produce and transport the main components like steel, concrete, and glass to that area.

People can also “claim” their properties on Carbon Title’s database and add more specific data to refine the estimates. While Trevor and Miles hope that we can get more sophisticated in the way that we understand a building’s carbon footprint, they don’t think that it will sway our decision making too much. Instead, they had a clear vision for how we need to think about reducing the carbon in our buildings. “the biggest impact we can have is to upgrade our existing buildings. We need to start seeing their embodied carbon as an asset to be protected,” said Haladay. Even if some building owners do decide to go the demolish and rebuild route, Haladay doesn’t see that as the end of the world. “New buildings using low-carbon materials will also be needed to meet our climate goals, plus they can inspire us and show us what is possible.”

There is certainly a lot more work that needs to be done in order to understand the carbon associated with our built world. Until we do, it will be hard to know whether or not to try and upgrade our existing buildings or just knock them down and replace them with more efficient ones.

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