An argument favoring historic preservation is that existing buildings and supporting infrastructure contain vast amounts of increasingly valuable “embodied energy”. In this time of global conflict over natural resources, nonstop damage to the environment, and rising oil prices, we can think of our stock of existing buildings, roadways, utility structures, etc. as a store of potential energy not to be wasted through replication or abandonment.
Simplistically stated, energy “embodied” in a material is that which is consumed over the life of the material from cradle to grave. In the building industry, it includes all the energy inputs along the chain, beginning with harvesting or extracting raw materials from the earth, to processing them into useful substances, to forming those substances into building components, to shipping those components to a construction site, and then lifting them into place. An extension of this chain would include the energy needed to repair, remove, recycle or dispose of the components. An ultimate calculation would include the energy consumed by workers in the supply chain, notably that which is used for personal transportation.
Similar measurements can be taken of other resource inputs, such as the amount of water needed to grow corn used to make ethanol. An oft-quoted measure is the amount of water and grain consumed by cattle to produce a pound of meat.
Construction uses vast amounts of materials and energy. In a 2005 report, the World Watch Institute estimated that buildings use 40% of all raw materials worldwide. In the U.S., they consume 39% of all primary energy produced, 70% of all electricity, and over 12% of potable water. Senior scientist Rob Watson of the National Resources Defense Council says this: “Buildings are far and away the worst thing humans do to the environment. The built environment devours half of all the world’s material and resources, half of all forests.”
At least one-third of all waste generated in this country comes from construction. An estimate by the Environmental Protection Agency showed that debris from building-related construction and demolition amounted to 136 million tons in one year (1997) alone. In comparison, 209 million tons of municipal solid waste was produced that year.
As an architect, this deeply concerns me. My ethical duty is to find ways to provide the shelter that people need without damaging the environment. The best way I know to do this is to reuse the buildings we already have. And one way to argue for these buildings is to measure the energy already consumed to create them, and relate it to energy costs and externalities today.
Finding measures of embodied energy is difficult. I have looked for reliable sources since the early 1980s when I first encountered the concept. An internet search I did for this article showed research being done in a very few places, including Canada, Australia and India. To determine the energy values of a single building component takes a tremendous amount of work, and there has been limited funding and interest, though I sense this will soon change. One driving force may be New York City’s new greenprint PlaNYC, which discusses the concept as a component of a huge energy efficiency effort.
From my internet search I gathered the following measures of embodied energy. Use these numbers with caution, as I was unable to verify their accuracy. Similar numbers appeared in several cited papers, however, and I believe they are sufficient to illustrate the idea. As I present them here, the numbers have no units of measure: I converted their energy values to multiples of the lowest value I found, that of locally gathered fieldstone. I assigned fieldstone a value of one, and related the other materials to this value. Thus, in the chart below, the manufacture and use of fiberglass insulation consumes over 38 times the amount used by fieldstone. So much for saving energy by insulating your home!
| locally gathered stone | 1 |
| concrete block | 1.2 |
| concrete | 1.65 |
| precast concrete | 2.53 |
| lumber | 3.16 |
| brick | 3.16 |
| gypsum board | 7.72 |
| recycled aluminum | 10.25 |
| plywood | 13.16 |
| glass | 20.12 |
| fiberglass insulation | 38.35 |
| steel | 4.05 |
| PVC | 88.6 |
| aluminum | 287 |
In defending our historic realm, we need to make our arguments crystal clear. Writing about the c.1910 Cobb Building in downtown Seattle, an 11-story structure converted from medical offices to apartments, Michael Wishkoski said this in the Seattle Daily Journal of Commerce back in March, 2006:
“The building’s roughly 308,000 bricks, each with an embodied energy value of 14,300 British Thermal Units, represent 4.4 million BTUs of energy expended in the original construction of the building, or 1.3 million kilowatt hours of electricity. Given that the average household in the US uses about 8,900 kilowatt-hours of electricity each year, these bricks are equivalent to the amount of energy needed to power 145 homes for a year. This is only one dimension of embodied energy savings for one material, not including the value of the labor to set them in place nearly a century ago.”
And that’s just the bricks. To argue clearly and succinctly that preservation is worthwhile, we need solid numbers. We’ve tried the economic arguments, which remain rather weakly supported, and now we can work on the energy arguments.
