Every year, roughly one billion square feet of buildings are demolished and replaced with new construction in the United States, according to a new report from Preservation Green Lab, and that number is likely to escalate. That’s a lot of CO2 emissions and materials that could easily be saved. Since new buildings are generally more shiny and exciting though, it’s easy to lose sight of the fact that the greenest building is almost always the one that’s already standing. It seems like common sense, but now we have the hard data to back it up. According to the highly-anticipated report, it can take up to 80 years for a new, energy-efficient building to overcome the environmental impact of the construction process.
Preservation Green Lab used life cycle analysis methodology to compare the environmental impact of new construction versus the renovation and reuse of existing buildings over a 75-year life span. The study looked at six different building types (single-family home, multifamily building, commercial office, urban mixed-use building, elementary school, warehouse conversion) located across four different climate zones (Portland, Phoenix, Chicago, and Atlanta), and found that reusing old buildings almost always has a slighter impact than tearing down and rebuilding. However, the authors of the study do acknowledge the environmental costs associated with renovating and reusing older buildings, observing that “the benefits of reuse can be reduced or negated based on the type and quantity of materials selected for a reuse project.” Interestingly, the only type of existing building in study that didn’t outperform new construction was the warehouse-to-multifamily conversion — a building type that has become increasingly popular in many urban areas — because of amount of materials needed to perform the conversion.
The environmental benefits of reusing existing buildings vary widely based on the type of building and location (it makes more sense to build new construction in places like Chicago than Portland, for example), but in almost all cases it will take several decades for a new ‘green’ building to overcome the environmental impact of the construction process relative to reuse. New buildings with solar panels, green roofs and energy-monitoring technology are fine, but when it comes to green cred, they’ve got nothing on existing buildings.