“The greenest building is the one that is already built.” As a reader of Green Building Advisor, if you haven’t come across this quote or some variation on it in the last few years, please post a picture of the rock you’ve been living under in the comments section.

By now this proclamation, coined by architect and climate advocate Carl Elefante, has evolved into adage, even gospel. But like gospel (religious or otherwise), its high standards can be difficult to uphold. While preservation of our built environment may benefit from a warmer political climate than what existed half a century ago, the allure of things shiny and new still captivates us. Consequently, because the economic value of a new residential or commercial development is fairly easy to measure, we have historically devalued existing buildings. That’s because we’ve been using the same criteria to measure new versus existing buildings. This is a calculative and conceptual error.

Building reuse and carbon

The holistic value of reusing an existing building (or rehabilitating and adding to it) versus razing it and constructing a new one is hard to quantify. Preservationists and conscientious urbanists alike are adept at qualifying the value of building reuse, often in terms of responsible stewardship, and complemented with associated cost savings. But when it comes to compiling hard data from an environmental perspective, and that can justify reuse in terms of avoided carbon, we remain lost in the woods. Well, kind of.

The CARE Tool (Carbon Avoided: Retrofit Estimator) is the brainchild of a small consortium made up of Larry Strain, founding principal at Siegel & Strain Architects; Erin McDade, senior program director at Architecture 2030; and Lori Ferriss, an architect specializing in preservation and the 2023 chair of AIA Committee On the Environment (COTE). What began in 2019 as a prototype written up and fine-tuned in Excel eventually evolved two years later into online platform—now part of Architecture 2030—that can be fed a vast range of datasets, from heating and cooling days to projected grid decarbonization timelines, depending on the location of the building. By design, the tool is meant to address the proverbial elephant in the building, that being scope 3 emissions.

Like most algorithms, the CARE Tool’s origins stem from a simple void in the market. If an owner of multifamily buildings or a college’s board of governors require data that will show the net climate impacts of reusing versus replacing a building, they now have such a calculator at their disposal, and a means of leveraging others to be better stewards without pontificating. According to McDade, when looking through an emissions lens, building professionals’ intuition that reuse trumps new construction is decades in the making. “The tool is really an attempt to take this intuitive sense that we’ve all had, and not only quantify it, but also make sure that we’re actually achieving [our emissions] goals,” she says. “Not every case study reveals a dramatic difference in embodied emissions, or even suggests that reuse makes sense. Still, it’s pretty rare that we see a case where reuse isn’t the smarter total carbon decision.”

One possible exception, Ferriss points out, could be a historic landmark building located in a region with a dirty grid, and renovating both the face and body of the structure is politically infeasible. “You can’t really improve its energy performance, but you can replace it with something net zero,” Ferriss says. “In that case, new construction probably makes sense because the operational emissions are such a high percentage of the total carbon footprint.”

Getting it right

The tool is free to use, but like performing an energy audit or lifecycle assessment, it’s not meant for the DIY set. And the data the tool provides are only as good as those soliciting it. “The tool has no use unless you have a client who thinks there is one,” says Mark Thompson Brandt, senior conservation architect with Ottawa-based Trace Architectures. Brandt’s firm has engaged with the CARE Tool on two occasions, with one client “still in the decision-making stage.” Nonetheless, he’s an outspoken champion of the tool’s broader implications.

To that end, Brandt mentions a statistic he often cites in his lectures which, while seemingly impossible to verify, does seem plausible. In the three decades following World War II (until approximately 1975), the global community constructed as much occupiable built space as all of humankind had constructed since the dawn of civilization. No matter how big the margin of error on that particular stat, one has to admit we have an awful lot of mid-century building stock that’s nearing (or already surpassed) its end of life. Lurking within all that, cumulatively, is an immeasurable amount of embodied carbon.

“We’ve been doing far too much demolition, needless demolition, for the last two generations or more,” Brandt says. “And we can save a hell of a lot of carbon by rehabilitating and conserving. Once our processes in the building industry are more in tune with fixing, repairing, and retrofitting, you end up with buildings that are very appealing to the public. We can save a lot of that 40% that the built environment contributes to global warming.”

Additional tools

The CARE Tool joins a growing cast of integrated and freestanding software available to architects, engineers, and consultants for measuring embodied carbon. Some like Beacon and Tally are plug-ins for Revit that enable building teams to perform whole building lifecycle assessments within their design models. Others like Pathfinder and EC3 (Embodied Carbon in Construction Calculator) are web-based calculators that perform similarly to CARE, with some notable deviations. The former is focused on sequestration for landscape and site design projects, while the latter offers teams access to a database of environmental product declarations (EPDs) that can be used to calculate realized or potential carbon reductions based on quantities of building materials, ranging from structural systems and enclosures to interior finishes.

McDade and Ferris both note that CARE is particularly suited to large-scale residential projects and should ideally be employed early in a project’s pre-design or design phases. Like a few other tools of its ilk, CARE’s data yields are not based on any specific materials or detailed quantities. So, to get a more comprehensive picture of a potential project’s carbon impacts, they recommend sequencing different tools. For instance, the Carbon Conscious App, developed by Sasaki, can be applied during early planning phases. This can be followed up with the CARE Tool to examine the impacts of reuse and “explore more nuanced ways of renovating,” Ferriss says. And finally (perhaps), this can be coupled with other free or subscription-based tools to compare specific materials.

The path forward

For the moment, the tool is built for measuring operational and embodied carbon data for the U.S. and other markets that employ similar building materials. The goal, according to CARE’s developers, is to broaden its scope threefold: to compute regional data by country, be adjustable for commercial buildings as well as single-family homes, and be capable of quantifying reuse strategies that apply to entire campuses or neighborhoods. “The national and global interest [in CARE] has been astounding,” McDade says.

“To meet our climate targets, we need to get [global reuse] to at least 10% [of our existing stock]. And the only way that we’re going to meet climate targets is if we upgrade and reuse as much of our buildings as possible.” Indeed, if we have any good faith designs on meeting the goals of the Paris Agreement, which means halving all building emissions by 2030, then our salvation lies in existing buildings.

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Justin R. Wolf is a Maine-based writer who covers green building trends and energy policy.