Reusing an old building pretty much always has less of an impact on the environment than tearing it down, trashing the debris, clearing the site, crafting new materials and putting up a replacement from scratch. This makes some basic sense, even without looking at the numbers.
But what if the new building is super energy-efficient? How do the two alternatives compare over a lifetime, across generations of use?
“We often come up against this argument that, ‘Oh well, the existing building could never compete with the new building in terms of energy efficiency,’” says Patrice Frey, the director of sustainability for the National Trust for Historic Preservation. “We wanted to model that.”
Preservation Green Lab, the Trust's sustainability think tank, has published a new study today examining this that puts big numbers behind the finding that the greenest buildings aren’t in fact state-of-the-art ones; they’re the ones we already have.
Retrofit an existing building to make it 30 percent more efficient, the study found, and it will essentially always remain a better bet for the environment than a new building built tomorrow with the same efficiencies. Take that new, more efficient building, though, and compare its life cycle to an average existing structure with no retrofitting, and it could still take up to 80 years for the new one to make up for the environmental impact of its initial construction.
The study looked at six types of buildings set in cities from four different climates: Phoenix, Chicago, Atlanta and Portland, Oregon. The building typologies modeled were commercial offices, warehouse conversions, urban village mixed-use buildings, elementary schools, single-family homes and multi-family residences. From every single one of these categories, in every climate, retrofitting the existing building produces less of an environmental impact than constructing a new one on the same plot of land. The lone exception was warehouses conversions to multi-family residences, a more intensive form of reuse.
The most interesting data lies in how new buildings compare to existing ones if we don’t even bother to retrofit them. This chart from the report shows how much time it would take for a new building that's 30 percent more efficient to overcome – through all that efficiency – the impact of its construction (much of which lies in the use of all that new material).
This means that you could put up a new mixed-use building in Portland that's 30 percent more efficient than an otherwise identical one across the street that already exists. It would still take 80 years for that new building to have – over its entire life cycle – the better environmental impact. That conclusion contradicts the common perception that we may innovate our way out of climate change with ever more efficient new stuff.
"This is a strategy that most policy-makers aren’t thinking about," Frey says. “Everyone wants a monument, a shiny new thing to put their name on, to make their mark. And I think some of it is just a cultural preference for new. We have a real estate industry that really – at least before the Great Recession – wasn’t particularly well attuned to dealing with existing buildings. The model was demolish the site, clear the site and build from scratch. That was the calculus they were used to.”
Some older estimates suggest that we have been demolishing and replacing about 1 billion square feet of buildings in the U.S. each year (OK, probably not during the economic downturn). And the Brookings Institution has projected that we could turn over as much as a quarter of all of our building stock by 2030.
In this context, Preservation Green Lab’s study suggests the city of Portland, for example, could meet 15 percent of its emissions-reduction goals over the next decade just by reusing the 1 percent of its buildings the city expects to demolish over that time. That’s not to say the most decrepit house must be saved (although that would make for a good Portlandia episode).
“We’re not coming out and saying ‘all buildings have to be reused,’ and ‘all new construction is bad,’” Frey says. “What we’re advocating for is a shift in thinking, where at a minimum, we’re considering the environmental impacts associated with demolishing places before we tear them down and build something new.”
Oh, and doing this would also give a bunch of us jobs!
Photo credit: Robert Galbraith/Reuters