Oh, the virtues and failures of Twitter; here is a little conversation from Saturday:
Mike at @bruteforceblog: Embodied energy and carbon are not good arguments for preservation. There are much more valid reasons.
Andrew at @wanderu: Has anyone published reasoned-out argument against embodied energy ?
@lloydalter: Two words: Sunk Cost.
@wanderu: Ah, microeconomics. Well, since microeconomics is bullshit, I'm not buying that argument.
OK, @wanderu, here is a longer answer.
Embodied Energy is a concept that is often used to justify the preservation of existing buildings rather than the building of new ones; It refers to the energy bound up in the making of the building's materials, transporting them to the site and constructing the building. Donovan Rypkema has written:
We all diligently recycle our Coke cans. It's a pain in the neck, but we do it because it's good for the environment. Here is a typical building in an American downtown — 25 feet wide and 120 feet deep. Today we tear down one small building like this in your downtown. We have now wiped out the entire environmental benefit from the last 1,344,000 aluminum cans that were recycled. We've not only wasted an historic building, we've wasted months of diligent recycling by the people of your community.
Robert Shipley has written in Alternatives:
Every brick in building required the burning of fossil fuel in its manufacture, and every piece of lumber was cut and transported using energy. As long as the building stands, that energy is there, serving a useful purpose. Trash a building and you trash its embodied energy too.
But is it really true? Is the energy there? Tristan Roberts at BuildingGreen doesn't think so. He wrote in Green Building Advisor:
Energy spent in construction is water under the bridge
We should save historic buildings because they are beautiful and because they are important to the fabric of our communities. Relative to the environment, they are often located in central, downtown locations that are pedestrian and mass-transit-friendly. While they aren't usually super-efficient, they are more energy-efficient than you might think. According to the quadrennial study of buildings in the U.S. by the Department of Energy (CBECS), buildings built before 1960 use less energy per square foot, on average, than buildings built since then.
However, when it comes to the energy expended in the 19th century to build that structure, that's not a good reason for saving a building from demolition — it's water under the bridge. Energy spent 2, 20, or 200 years ago to build a building simply isn't a resource to us today.
I used the term Sunk Costs to say much the same thing. According to Wikipedia:
Traditional economics proposes that an economic actor not let sunk costs influence one's decisions, because doing so would not be rationally assessing a decision exclusively on its own merits. The decision-maker may make rational decisions according to their own incentives; these incentives may dictate different decisions than would be dictated by efficiency or profitability, and this is considered an incentive problem and distinct from a sunk cost problem.
And Seth Godin:
When making a choice between two options, only consider what's going to happen in the future, not which investments you've made in the past. The past investments are over, lost, gone forever. They are irrelevant to the future.
Discussing and valuing the embodied energy of the building's original construction is a tough sell, because people are wired to look forward, not back, and have been trained to downplay sunk costs. What matters to our environment is the carbon dioxide we are putting into the air now. The embodied energy that matters is that which is in the energy of the demolition of the existing structure and the construction of its replacement. In one study by Mike Jackson, Embodied Energy and Historic Preservation: A Needed Reassessment (lousy pdf here)
Jackson demonstrates that new buildings’ life span must reach 26 years to save more energy than the continued use of an existing building. As building energy efficiency increases, embodied energy consumes an even larger proportion of life cycle energy consumption. Jackson finds that if a building were demolished and partially salvaged and replaced with a new energy efficient building, it would take 65 years to recover the energy lost in demolishing a building and reconstructing a new structure in its place. That is longer than many modern buildings survive.
Preserving and upgrading a building is far more energy and carbon efficient than knocking it down and building new. Calling the new building "green" when it replaces an existing building is a farce when it takes so much energy to build. But what matters is the embodied energy of the future building, not the past.