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Retrofits (Usually) Greener Than New Construction, Study Says

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By Paula Melton


Carbon payback times vary considerably by climate and building type, but the new report shows that reuse, even without energy performance improvements, almost always trumps demolition and new construction.

Source: Preservation Green Lab, National Trust for Historic Preservation

Is the greenest building the one you don’t build? The answer is a resounding “usually.”

Conventional wisdom about building reuse is questioned and quantified in a much-anticipated report released today by Preservation Green Lab, part of the National Trust for Historic Preservation. Using a life-cycle assessment (LCA) approach that takes both operational and embodied impacts into account, the report compares the environmental impact of retrofitting an existing building for high performance vs. tearing down the building and replacing it with a high-performance one. It also looks at a more common real-world scenario—pitting high-performance new construction against continued use of a building that has only average energy performance.

While reuse generally has less impact, the advantages of retrofitting vary greatly depending on building type, climate, and materials used. In one notable exception to the overall results, adaptive reuse of warehouses for multifamily housing can actually have a greater environmental impact than demolition and new construction—highlighting the fact that decisions about retrofit vs. demolition will still need to be made on a case-by-case basis.

Carbon payback

The most catastrophic effects of climate change can only be prevented in the next 20 years or so, making global warming potential one of the most pressing environmental impacts to consider. Since it can take decades for a new building to “pay back” its embodied carbon through improvements in operational efficiency (see “A 2030 Challenge for Building Product Manufacturers,” EBN Feb. 2011), this study’s conclusions about carbon emissions should come as no surprise: based on climate-change considerations alone, almost every useable building in every region of the U.S. should remain standing—even if these buildings are not retrofitted to improve energy performance. Carbon payback time for the buildings studied ranged from 10 to 80 years.

Important caveats

While showing the clear benefits of building reuse, the report cautions that “reuse alone cannot fulfill the urgent task of reducing climate change emissions,” adding, “Reuse and retrofitting for energy efficiency together offer the most significant emissions reductions.”

Even when a retrofit is undertaken, the materials used in the retrofit must be carefully chosen. If the building footprint is expanded or if materials with high embodied energy are chosen, “the environmental benefits of reuse can be eroded or substantially eliminated.” Materials used for energy-efficiency measures can also harm human health and ecosystem quality.

“One of the results that I find interesting is just how much materials do matter,” said Jason McLennan, CEO at Cascadia Green Building Council and one of the study’s lead researchers. “If you are completely gutting a building and putting in tons of new materials, it’s beginning to act not like reuse” but instead like new construction. Buildings that are easily adaptable or those that can fulfill program requirements without added materials appear to be better choices for reuse, he said. “Existing building reuse is an incredibly important part of a strategy for energy reduction. It needs to be at the top of the list.”

Unique methodology

The study’s methodology is unusual, combining large datasets with case studies of particular buildings. Energy-performance projections were based on national survey data, while case studies were used to determine the relative embodied impacts of retrofitting vs. new construction. While this methodology could leave the study results open to critique, the report claims this choice helped researchers accurately capture the complexity of comparing retrofits with new construction. The results, they say, actually increase the data’s reliability since embodied impact estimates were based on actual retrofit and construction projects rather than on modeling. Researchers call for further study to compare the status quo with more aspirational construction scenarios, such as net-zero-energy construction, lower-impact material choices, and increased urban density.

The Preservation Green Lab completed the study in partnership with Cascadia Green Building Council, Green Building Services, Skanska, and Quantis.

For more information:

National Trust for Historic Preservation



Comments (6)

1 Gets interested with Net Zero posted by Brad Jacobson on 01/30/2012 at 06:46 am

Fascinating study. We did a similar study for a Net Zero energy office project nearly completed for the Packard Foundaiton. A board member questioned whether they should just stay in the current building if considering climate alone. We found that based on actual operational energy use of the current building, the NZE building -- built with extremely low-embodied energy materials like 70% cement-replacement concrete and mostly wood structure -- would pay back in around 4 years.

I agree with the study's methodology: you have to look at specific case studies because generalizations in this area are nearly useless.

Brad Jacobson EHDD Architecture

2 Drawing the Wrong Conclusions posted by Rob Harrison on 01/30/2012 at 03:40 pm

In his comment Brad Jacobsen certainly hits one of the nails on the head. The assumption of a 30% energy savings in the "advanced case" of the study is a very low bar, given what is possible now with Net Zero Energy and Passive House.

There is an ever more basic issue with the study. The all-caps key finding is:


The footnote says:

"2. where energy performance for renovated and new buildings is assumed to be the same."

Well (forgive me, but)...duh! If operating energy is assumed to be the same for both new and retrofitted buildings in the study, the only difference in total energy use is the embodied energy saved by reusing the existing building. Of *course* it's going to "save energy" to use an existing building if you examine the question through that lens!

In addition, the study acknowledges that it does not take into account the energy-saving effects of increasing density, or knock-on effects of reducing transportation energy. An existing one-story commercial building almost never gets replaced by a new one-story building. It would rarely pencil out. Dunn and Hobbes' Agnes Lofts in Seattle is a beautiful example of densification that (I assume) made economic sense. (Liz Dunn is one of the authors of the study.)

Net-Zero and Passive House are more difficult to achieve in retrofits than in new construction, but the energy savings of both of those approaches are substantially more than 30%. According to the 2030 Challenge, we're supposed to be achieving 60% reductions this year. Why are we even proposing scenarios of "advanced cases" that assume only 30% savings? Which path offers a clear, cost-effective way to meeting Architecture 2030 goals, new construction or retrofit? That question must be asked and answered for every project, rather than through gross generalizations.

I'm surprised that Building Green has not examined this study with a more critical eye.

I've written a more detailed response on my blog, here:

3 "Carbo-centric" posted by Michael Poloukhine on 01/30/2012 at 03:42 pm

Too bad they based all that effort on increasingly questionable presumptions about atmospheric Carbon impact on climate. Better to have worked it around embodied energy and resource efficiency in a more absolute manner and let the presumption of Carbon importance be a factor that could be applied over the study results. As the "incontrovertible" assumptions about Carbon driven global warming get exposed to be not so incontrovertible after all, studies of resource and energy efficiency like this one become obsolete or useless while the issue of conservation of energy, resources or work effort (not to mention historic preservation) remain just as important to a sustainable world as they ever were.

4 Thanks, Rob! posted by Paula Melton on 01/31/2012 at 01:51 am

To be honest, I too had that "duh" reaction about the base case vs. advanced case. I did look at the study rather critically for that very reason, and I think there are two reasons this particular aspect of the study--and it's only one aspect--is significant despite the rather obvious nature of those conclusions.

1. It quantifies for many different building types just how much of a difference embodied energy makes. For some buildings, it's a lot; for others, not so much. And there is one case, as you probably noticed, in which retrofitting is more environmentally intensive than tearing down and rebuilding.

2. It sets the stage for further study, which the authors quite explicitly ask others to conduct. They are the ones who bring up the major missing pieces--net-zero buildings and density considerations. They feel they've laid the groundwork for those further studies to happen. I don't think they disagree with you!

I do think that you might be overestimating what counts as "advanced" for most people, but hopefully we can continue moving the needle on that. One big question for me was whether 30% was so readily achievable in retrofit projects. That's the assumption that I find hardest to swallow.

As for the study overall, I think it would have been far less significant if it had stopped at the 30%-to-30% comparison. The chart included with the article above is where the rubber really hits the road, from my point of view: it compares an existing, average building with a new, high-performing building (and takes demolition into account). It's easy to assume that tearing down a ho-hum building and replacing it with a LEED Gold one is necessarily better--but the numbers tell us that it can take a really long time to make up for those impacts, even if the old building had NOT been retrofitted for better energy performance.

The other significant thing I see from this study is that preserving an old building and increasing the footprint (another more realistic scenario than a 30% better retrofit vs. a 30% better new building) doesn't necessarily pan out. Once you start building additions and doing energy retrofits on the existing part of the building, there are times when you might as well be tearing down and building new. That's when other factors--like just how good the new building could be and just how historically significant the old building is--come into play. But you may no longer have much of a leg to stand on as far as the environmental case.

People will definitely still need to make these decisions case by case, and I do hope the article did not give anyone the impression that it's otherwise. Not every building is worth preserving. Not every new building is going to preform better than an old one.

One thing that I think would have been a good companion to this study is a tool that people could use to help them decide whether a retrofit or teardown/rebuild was the better environmental choice. Now THAT would be cool!

5 Window Restoration vs Window posted by catherine brooks on 02/17/2012 at 02:37 pm

This past summer the Window Preservation Standards Coalition funded air infiltration testing on windows in a historic school in KY. The baseline testing was done before the restoration of the windows. Several traditional techniques and modern technologies were used to restore both old wood and steel casement windows and to provide storm windows. The cost of different techniques ranged from under $50 to several hundred dollars. The craftspeople performing the restorations had between 5-30 years of experience restoring windows.

The goal of the testing is to provide the public and project specifiers with concrete data to present window restoration as viable cost and energy-efficient alternative. To date the high dollar marketing campaigns of the national Window Replacement companies have convinced most of us that replacement with high tech windows is the best solution.

The results of the study will be released and publicized spring 2012.

6 Window restoration study posted by Paula Melton on 02/20/2012 at 04:14 am

Catherine, we'd really appreciate getting more info from this study when it's available. Please keep us in the loop at Thanks!

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January 24, 2012