Old buildings, especially those in disrepair, tend to be drafty places. More air leaks lead to more heating and cooling—and ballooning utility bills and emissions. That’s a huge deal, because the construction and operation of infrastructure accounts for nearly 40% of global greenhouse gases.
The answer seems simple, in that case: Start fresh, build more efficiently. But retiring old buildings isn’t necessarily the best option. (As Carl Elefante, former president of the American Institute of Architects, once said, “The greenest building is…one that is already built.”) For at least a decade, research has shown that it’s almost always better for the climate to retrofit and renovate. This body of work, though, has largely centered on generalizations and hasn’t looked at actual structures in a city. New analysis published earlier this year in the journal Carbon Management, however, has found that remodeling is likely the best option for literally every building.
The carbon costs of building
A building’s carbon use goes beyond the emissions from its operation such as electricity, heating, and cooling, explains an author of the new study, Ming Hu, an architecture professor at the University of Notre Dame. Rather, it includes so-called embodied carbon that encapsulates the edifice’s full life cycle, from extracting materials and transporting them to the site, to building the structure and eventually demolishing it. For instance, concrete is responsible for a large chunk of infrastructure emissions because one of its main ingredients, clinker, is produced by heating limestone to super high temperatures. Because of this, concrete is responsible for 7% of global carbon emissions.
When weighing fixing the old against starting new, once you account for all of that—plus any new materials needed for rebuilding—it’s significantly greener to renovate. According to one calculation, revamping an older house rather than erecting a new one saves the carbon equivalent of 93 cars driving a full year; doing the same with a commercial building equals 1,028 cars. These numbers hold even when daily operations wouldn’t be as energy efficient as they otherwise could be in a shiny new build like a passive house.
Hu’s study in particular used machine learning to analyze the carbon trade-off of renovating versus rebuilding for more than a million buildings in Chicago. They found that constructing new, green buildings was the more carbon-efficient option in exactly zero scenarios. Which makes sense: A 2012 analysis from the Preservation Green Lab at the National Trust for Historic Preservation found that it can take up to 80 years for the energy savings of rebuilding with a greener design to make up for the carbon cost of construction.
Next, Hu will tackle other cities, many of which have newer buildings than Chicago does, to see how the carbon trade-off shakes out.
Alternatives to demolition
As anyone who’s watched too much HGTV knows, though, renovation can be dicey business. Old buildings often lack detailed notes about their structure, making retrofitting difficult, Hu says. This is particularly true if a developer is repurposing buildings for something completely different, like turning a warehouse into housing. It’s much easier to start from a blank slate. Fortunately, it’s usually cheaper to renovate, even if it is the harder option, Hu says.
There is also a middle ground: using old buildings for parts. When decommissioned buildings are blown up or torn down, much of their innards end up in landfills. But the “design for deconstruction” movement is pushing for the industry to design new buildings with recycling in mind. “If something from one life cycle can be put into another life cycle, then the entire economy, and entire society, will be better off,” Hu says. Recycling and reusing isn’t necessarily as planet-friendly as renovating, but it’s still better than getting stuck in a build-from-scratch, demo, build-from-scratch cycle.