ASK THE EXPERTS: Embodied Energy

Intermediate

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Straw Bale Home Construction
If the high ecological costs of industrial agriculture are not included in the embedded energy calculations for straw bales, we are only cheating ourselves.

In the natural building article in HP99, there is a table indicating embedded energy values for various natural building materials. I see that straw bales are listed as having the lowest embedded energy—lower even than earth! I am curious to know how the authors compiled this information, and I am dubious that the value for straw is correct when the true cost of the material is considered.

The vast majority of straw available in industrial nations such as the U.S. is the product of an incredibly energy (and chemical) intensive, soil and ecosystem-destroying, completely fossil fuel dependent mechanized agricultural process. Have all these costs in production of straw bales been factored in to the embedded energy value listed for straw? How about transportation costs when straw bales are not a local resource?

Straw bales are one of a variety of alternative building materials. It is important that natural builders and natural building advocates tell the whole truth about the costs of materials they use and recommend. If the high ecological costs of industrial agriculture are not included in the embedded energy calculations for straw bales, we are only cheating ourselves.

John Schinnerer • via e-mail

You bring up some excellent points that stress the difficulty in calculating embodied energy of building materials. The embodied energy coefficients we mentioned in the article are based on a 1983 study conducted by the New Zealand Energy Research and Development Committee, updated in 1997 by the Building Research Association of New Zealand. This study has long been used worldwide as a reference document on embodied energy. Nevertheless, estimates of embodied energy can vary greatly depending on how the assessment is done. While straw bales are inherently low in embodied energy, as you point out, most have been sprayed with fertilizers and pesticides, produced by fossil-fueled machinery, tied together by plastic twine, and may end up being transported over hundreds of kilometers. This can add significant amounts of embodied energy to what is a fundamentally low energy material.

However, in the United States each year, more than 200 million tons of waste straw is produced. Since straw is a waste product that cannot be used for feed like hay, much of it is burned at the end of the season. Some researchers do not to include the embodied energy of the production and cultivation of straw, since straw is just a by-product of the primary plant. It’s similar to not including the embodied energy of the manufacture of tires in an Earthship, since the tires are being recycled. We also must remember that the burning of waste straw emits large amounts of carbon monoxide and nitrous oxide into the air. Using straw bales reduces the poisonous gases in the air. Also, the straw left over from building can be used as mulch so that, overall, there is minimal real waste from using the material.

The reason that the embodied energy of straw bales is lower than that of the earthen technologies is the fact that (assuming the straw is grown relatively locally) earth takes a lot of energy to move. It also requires energy to press into blocks or ram into forms. Also rammed earth is often stabilized with cement, a very high embodied-energy material. For information on how the New Zealand organizations came up with the embodied energy coefficients, you can download their report at www.arch.vuw.ac.nz/cbpr/embodied_energy/files/1995.pdf

Keep in mind that figures often quoted for embodied energy are broad guidelines only, and should not be taken as exact. What is important to consider are the relative relationships. Try to use materials that have a lower environmental impact, and work best for your location, climate, and needs. The bottom line is, it’s hard to argue that both earth and straw aren’t among the greenest of building materials.

Laurie Stone, Solar Energy International

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