To Save Carbon, Rebuild or Retrofit?

Ask anyone who owns an apartment how much it costs to live there, and they’ll tell you it’s more than just the monthly maintenance fees. They’ll include their mortgage – how much it cost to buy the unit in the first place. Ask most people how much energy a building uses, and you will probably hear about its annual consumption. But this leaves something out: the energy it cost to put the building up in the first place. By looking at what it takes to manufacture, transport and assemble building materials, or “embodied energy,” we can get a more complete assessment of the energy and carbon impacts of a building.

It’s not surprising that few account for embodied energy. Without knowing where every scrap of material came from and how it was made—and who does, for an old building?—it’s impossible to accurately measure. There’s no industry consensus on how to even make a guess, and even if you do, what’s the point? Unlike the equity you may have in your home, there’s no way to recoup any value.[1]

But is that the end of the story? Michael Adlerstein[2] directed the United Nations Headquarters renovation, a project so big that Urban Green has covered it twice already. During the project, Adlerstein began to wonder: while buildings get replaced infrequently in NYC, there still has to be some embodied energy penalty for putting up a new building instead of continuing to use the one that’s there[3]. Of course, renovations themselves add new embodied energy during construction.

But comparing the embodied energy of a retrofit vs. new construction is only half the story. What about the operational energy used? Will the spiffy new building use less energy because it can take advantage of new technologies and is built to modern code? Or will it add window area and decrease thermal mass, potentially performing worse than what it replaced? Gee, it depends, which means…time for a study!

So Adlerstein[4] took a careful look at the UN HQ options. He concluded that although a new building would have been more energy efficient—i.e., used less operational energy on an annual basis—that counting embodied energy, renovation was the way to go. The published report, Assessing the Carbon‐Saving Value of Retrofitting versus Demolition and New Construction at the United Nations Headquarters[5], concluded that:

If the UN complex had been demolished and replaced with new construction of similar size, it would have taken between 35 – 70 years before the improved operating efficiencies of the new complex would have offset the initial outlays of carbon emissions associated with the demolition and new construction process.”

What does this mean for citywide energy and carbon reduction goals? Are the UN’s results typical of the building industry as a whole? If so, does NYC need to prioritize renovations over demolition and new construction – even if the new buildings are more energy-efficient than what they replace?

Join Adlerstein, John Amatruda (Vidaris), and Kris Baker (Syska Hennessy) on April 24 at UN HQ Report: The Carbon Case for Retrofits to get the full story and discuss this intriguing take on a more thorough approach to carbon reduction. I look forward to seeing you there[6]!



[1] Exception: burning bits of the New York Public Library to stay warm during an overnight ice age in Day After Tomorrow.

[2] He’s also Assistant Secretary‐General and an ace raconteur. Ask him about the drapes in the Security Council chamber sometime!

[3] Others have done so as well, notably Midcentury (Un)Modern, Terrapin Bright Green’s study of midtown office buildings (which Urban Green reviewed), and The Greenest Building: Quantifying the Environmental Value of Building Reuse by National Trust for Historic Preservation.

[4] With help from Vidaris and Syska Hennessy. Full disclosure: Urban Green reviewed a pre-publication version of the report.

[5] We can all agree that after working so hard to conserve energy and carbon, reducing TWUI (Title Word Utilization Intensity) seems practically besides the point.

[6] Bring a reliable embodied energy reference that’s more recent than Cole and Kennan’s 1996 study and I might just buy you a drink afterwards.