by Jacob Corvidae

Lots of folks are touting a new study by The National Trust for Historic Preservation claiming that re-habbing existing buildings is far more green than building new energy efficient buildings — but it’s not at all clear this is accurate.

The study itself is an impressive effort, and I laud their rigorous attempt to dig into this question. But they might be wrong, even though reports are flying around talking about about why you need to rehab instead of build new energy efficient buildings.

My concern is three-fold:

  1. A study done at University of Michigan found the opposite result. This study compared the LCA (life cycle analysis) of new construction single family residences, one energy efficient and the not. This found that the ongoing energy use of the buildings outweighed the carbon impact of the materials used by at least 4 to 1, and that was only over a 50 year lifespan (the new study uses a 75 year span). The results clearly indicated that energy use mattered more than the material use for the LCA.
  2. The National Trust’s own study shows that in a variety of contexts (depending on building type and climate) 10-12 years is all it takes for the energy use of the building to “catch up” with the embodied energy of the materials. When a building’s anticipated lifespan is 50-75 years, then this confirms the University of Michigan study.
  3. Finally, the new study compares rehabbed buildings to new energy efficient buildings and assumes that the new buildings are a notable 30% more efficient. Depending on the age, type of building and climate, I think this number may be misleadingly low and therefore harms the conclusion of the study. Residential construction in Michigan, for example, had such horrible energy codes until 2008, that a new energy efficient home (especially one that’s built green with a low HERS or ENERGYSTAR index) could easily be 40% more efficient and possibly more.

The new results may be accurate, but there’s plenty of reasons to wait before claiming that new truly energy efficient construction is worse than rehab.

Btw, some disclaimers:

  1. I have a strong interest and dedication to rehabbing buildings and historic preservation in my personal life and career — which is all the more reason why I want to be clear where the benefits and trade-offs really are.
  2. despite being right by the University of Michigan, I have no connection to the authors or department which produced the report.

10 Responses to “New green study may be wrong – new efficient buildings vs. green rehab”

  1. I only had a chance to skim the study but I wonder if in some of their cases they are comparing apples and pears.

    For instance in the retrofitted single family home they do not include air conditioning in the retrofit, whereas the new construction has A/C.

    Similarly the mixed use commercial has the retrofit get a ground source heat pump while the construction has a comparatively inefficient rooftop unit.

    Am I missing something?

  2. Youch. I only skimmed the studies too — but that sounds like bad controls on the study. Sure, you’ll show a better LCA on the retrofit if they use a lot less energy!! Rrrgg…. All the more annoying how much this is getting popped around….

  3. Bill Marston LEED AP
    11:58, 28.01.2012

    This thesis for a Masters degree was submitted for academic rqmts in 1998. In e-e building metrics & technologies, that is a long time ago.

  4. Yes, Bill, it’s a while ago, but the degree to which EE technologies have gotten better would only further my point. As for the EE measurement tools themselves…. I believe that study was done with the HERS system. While that systems has seen a few improvements, it hasnt changed much, and is still the national standard for residential energy measurement behind everything out there including ENERGYSTAR, LEED, NAHB green homes, etc. And while the industry is making improvements thankfully, it’s not as though the physics of energy use has changed in 15 years, so I’d neednt be surprising if their data is still accurate. THAT said, yeah, the 1998 study might be off — but the degree of discrepancy between the two studies is still sufficient to remain skeptical about the other study’s results. Which one is right? I don’t know, but all the more reason I want to stop this wave of declaring that the “truth” has been proven, when it hasn’t.

  5. Penn Taylor
    02:13, 29.01.2012

    I just can’t help but mention that any talk of a building’s energy efficiency is utter nonsense. Fuel economy, yes. LCA, yes. Embodied energy, yes. But not energy efficiency.

  6. Penn, can you elaborate?

  7. Diane Van Buren
    23:01, 29.01.2012

    A few thoughts – but the first that comes to mind is the sad concept that a house is built for a life expectancy of only 50 years. Holy cow – that means my house is obsolete and come to think of it – so am I! so – some of the figures have to be adjusted for rehab according to the double – and triple lifespan of the “average” home due to the higher quality of construction materials and embodied energy in them that does not have to be repeated again and again. Can a home built with today’s construction methods and codes meet the test of time? My 90 year old house does not have air-conditioning – we only have a few days a year when the central staircase can’t draw the air up and out of the house. so – hard to compare systems and construction comparison to find a reputable analysis. I know the preservation community depends on the adage that the greenest building is already built – so the debate will undoubtedly continue!

  8. Agreed about the 50 year span being too short — but that’s some of the point. Even when that was considered the case in the Umich study, it found the Life Cycle of the materials was much less of a factor than the energy used. And the thing is that you CAN compare these traits in different buildings. The new study compared buildings with antiquated systems to buildings with new efficient systems. If the antiquated systems work – great, but when you’re comparing an old boiler to a new geothermal system, it’s not a real comparison.

    You know, I’m a big believer in rehab — and there are many many good reasons for it. Personally, I just LIKE a lot of those older buildings more, and the history infuses a space with meaning — this is important! And other reasons reside as well — but I don’t want to claim that it’s better for our carbon footprint if it isn’t. What I want is a more reliable study.

  9. Just had an email conversation with some colleagues about this. They suggested that the point of the study wasn’t so much that retrofits were inherently better than new build, but that with serious energy effficiency, retrofits then have a clearly better LCA. I think this is the right direction to take the conversation, but for me it drive the focus in new ways. Here was my reply below.

    The basic gist: It’s really all about the energy efficiency much more so than about the materials in either direction – at least for residential. The question of the dollars and effort required to get as energy efficient as possible is the key — and how does new vs. retrofit effect THAT?

    Certainly if you make sure existing homes are made not just a little but way more energy efficient, then things start to look a lot better. But doing deep retrofits is not always easy. Take a house I worked on in Ann Arbor: it was built with 2x3s! We blew in foam and it helped, but the only way to really get that thing decent is to remove all of the siding, add additional insulation and then re-side the house. We also had to re-do the windows (they were single-pane aluminum – one of the few times I’ll advocate for replacing windows at this point). Throw in an upgraded furnace and all of these efforts together put the house outside of it’s marketable value. But I could BUILD a comparable house with much better energy performance for less overall money.

    Obviously part of the problem here is the financial context, right? And we need to fix how energy efficiency affects appraisals and home value — but in the meantime… I truly don’t know. The real question comes down to this: regardless of retrofit vs. new — how energy-intensive is the building designed to be for it’s operation? In either case, a bunch of factors from status quo to codes to appraisal systems to financing options all push people to do little to no energy improvements, and at that point, new vs. retrofit may not matter so much for the LCA. The real issue is how much you reduce the energy use by. So then we’re looking at cost and ease of implementation factors for creating seriously energy efficient spaces between new and retrofit, which is NOT what this study really does — and I think it may often be cheaper, and therefore more effective to make new building MORE energy efficient than a retrofitted existing building. At least for residential. It may be a very different story for a variety of other building types. THAT’s what I want to know, and that’s what this report implies, but I think it doesn’t know either.

    We have other good reasons to invest in existing buildings, from cultural and historic to aesthetic considerations. Of course, we want to reduce our impact on materials waste. These are all good things. But if we want to talk what has the biggest impact on the environment for stopping climate change, that may be a different issue.

    The study you sent is great – (See: — lots of good info. As for this topic, it only proves my point further. They all acheived LEED, but with minimal energy attention. Here’s how the 4 projects did for the Energy section, showing how many points they got out of how many possible for the Energy section of LEED: 4 out of 38; 4 out of 38, 5 out of 17, and 0 out of 38. They DIDN’T TACKLE ENERGY because it was hard to do so in an economically reasonable way.

    Am I missing anything here?

  10. Jacob, I’m not sure this proves your point further. LEED for Homes has ENERGY STAR for Homes as a prerequisite. You can’t get LEED certified, at any level, without meeting this standard. So the homes already have good energy performance compared with code. You can get extra points for “exceptional” energy performance, but you have to do at least pretty good to get the certification. So I would argue that you can get 0 points, but still have had to tackle energy to bring an old building up to a level that’s significantly better than current code.

    What’s even better is that ENERGY STAR gets updated as new codes come out, so that it continues to get stricter. For instance, the current ENERGY STAR for homes requires the building to be “at least 15% more energy efficient than homes built to the 2009 International Energy Conservation Code (IECC)”. That’s stricter than this study from 2008 would have had to be.

    As codes get tighter (and the latest, IECC-2012 and ASHRAE 90.1-2010, are much more stringent than their predecessors), just meeting code becomes less laughable as a design goal. We’re raising the floor for the lowest common denominator, and at the same time stretching the envelope with exceptionally high-performing buildings like Passive House.

Leave a Reply