Tuesday, February 11, 2014

Embody This

By Jason Yots

Historic preservation advocacy is delivered in many forms – economic, environmental, aesthetic, political, moral, ethical.  Some concepts are more accessible than others, but they all share a goal: to promote historic preservation as a path toward more sustainable living.

Perhaps the most direct path to that goal is the historic preservation argument built on the notion of “embodied energy.”  Before you jump back to Reddit, hear me out.  This is actually pretty interesting stuff, especially if you like to geek-out on preservation stats.

Let’s start with some dictionary.  One way to define “embodied energy” is “the energy required to extract, process, manufacture, transport, and install building materials” (Note #1).  In other words, it’s the collective energy required to bring a new building into the world.  Compare this to “operating energy” – the energy expended in using the building – and you’ll see that we’re heading into some new theoretical territory.

Most “green building” efforts focus on the operating energy side of the equation, where the primary focus is on building the most energy-efficient structure possible (within your budget, of course).  The proliferation of the U.S. Green Building Council’s “LEED” energy ratings for new and existing buildings is an example of this emphasis.  However, particularly where a building will be demolished and replaced by a new building, a tight new building envelope and efficient new systems are only part of the analysis, argue some preservationists.  In that scenario, one must also factor in the embodied energy that is squandered when a building with a remaining useful life is demolished and landfilled.  When you do, “green” buildings become, well, less green.

Still a little fuzzy?  Maybe some math might help.   The May T. Watts Appreciation Society created an intriguing online program called “The Embodied Energy Calculator” (Note #2).  Using only your building’s type and its gross square footage, the EEC estimates your embodied energy investment in a building.  The EEC also calculates the “demolition energy” that would be generated by demolishing a building by factoring its construction type and its gross square footage.

Let’s say that Developer plans to demolish a 25,000 sf masonry building to construct a similarly sized “green” building on the same site.

41,000,000 – mBTUs (Note #3) expended to build the tear-down
     387,500 – mBTUs expended to demolish the tear-down
41,000,000 – mBTUs expended to construct the new-build
82,387,500 – total mBTUs to construct the new-build

How much energy is 82,387,500 mBTUs?  One measure would be the equivalent of 716,413 gallons of gasoline, or enough to propel my Honda CR-V over 14 million miles.  Yeah, that’s a lot of energy for one medium-sized building, however green it may be.

Based on this methodology, then, a building’s overall efficiency would seem to depend heavily on the decision to include in the equation the embodied energy from the construction and demolition of the building it replaced.  Whether that's a fair measurement of a building's energy efficiency may be debatable but the adage “the greenest building is the one already built” certainly merits serious consideration.

1 – Wayne Curtis, “A Cautionary Tale.”  Preservation (Jan./Feb. 2008).

3 – One mBTU = 1000 British Thermal Units.

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