Assessing Green Building Materials: Page 4 of 5

Beginner

Inside this Article

The notion of building green has become mainstream in recent decades, thanks to the efforts of a small number of builders on the fringe of the building industry.
High-performance doesn’t necessarily equate to “green”—for example, petroleum products, such as foam insulation, have high embodied energy and major impacts on ecosystems.
Concrete has advantageous building and thermal properties, but is high in embodied energy and very high in carbon dioxide emissions.
Lumber is a renewable resource, albeit slow to regenerate. Its embodied energy depends on the distance between origin and use.
Straw bales are an agricultural “waste” product, with low embodied energy and good thermal performance.
Forest products may travel long distances between their material harvest and end use, which drives up their embodied energy.
Often, it’s the final energy performance of the structure that dominates its classification as being “green.” But this is only one aspect of an ecofriendlier building.
Per ton-mile, ships use only 1.3% of the fuel consumed by trucks. However, goods are usually transported over longer distances, resulting in high embodied energy.
Trains use only 0.8% of the fuel used by trucks to move freight; shipping by train significantly reduces a product’s embodied energy due to transportation.
When available, natural building materials, sourced and processed locally, are often the best bet for “green” solutions.

Transportation Impacts

An average house uses about 175 tons of materials, so transportation impacts can be a high proportion of the building’s total embodied energy. The distance materials must travel to reach your building site, the weight of those materials, and the mode(s) of transportation all impact a material’s embodied energy and “greenness.” The U.S. Department of Energy estimated the following for freight transportation in 2006:

Trucks: 4,074 Btu (0.3 gal. diesel fuel) per ton-mile

Rail: 330 Btu (0.0025 gal. diesel fuel) per ton-mile

Ship: 571 Btu (0.004 gal. diesel fuel) per ton-mile

The raw materials for construction products are often close to the point of manufacturing, but distances to point-of-use can be quite long. If your project needs 1 ton of insulation material, as little as 30 gallons of diesel fuel might be consumed if you are 100 miles from the manufacturer—or as many as 900 gallons of diesel might be used if the material has to cross the entire country to reach you.

Materials that travel by rail or sea have lower impacts per travel mile, but tend to cover long distances. For example, 1 ton of insulation coming from China may travel upward of 6,000 miles and use as little as 24 gallons of diesel fuel. However, that insulation must travel from a sea freight terminal to its final destination—which may be hundreds or thousands of miles away by truck. Only thorough research can give you an accurate sense of the transportation impacts.

Comparing Like to Like

Once choices are narrowed to a particular product or system, there can still be major impacts based on brand or supplier. Consider lumber products: While embodied energy and life-cycle figures are similar for all trees, the specifics of how and where they were harvested and processed can reveal a wide range of impacts. Poor cutting practices can be devastating to local ecosystems, destroying wildlife habitat, encouraging soil erosion, and negatively affecting waterways. Milling operations can be major polluters of air and water, and transporting lumber over long distances consumes vast amounts of fossil fuels.

Comments (4)

Byrdhouse9's picture

The article in the paper magazine includes a table called "Comparing Materials", showing the embodied energy per kilogram for various insulation materials. Is there data available that corrects for the fact that some kinds of insulation provide much more R value per unit weight than others? Light insulation like fiberglass and polyurethane foam would fare much better if the comparison showed energy per unit of R value.

Michael Welch's picture

Energy per R-value would be a great indicator to have.

Byrdhouse9's picture

There is a typo in the "Transportation Impacts" paragraph. The 0.3 gallons of fuel per ton mile for trucks should be 0.03. Typical mid-size trucks achieve this, and heavy trucks often do as well as 0.01 gallons per ton mile. For example, my old F-350 gets a pathetic 10 miles per gallon when hauling 3 tons, but that works out to 0.033 gallons per ton mile .

Allise Burris's picture

Sliding that decimal would mean that ships and trains consume approximately 10% and 30%, respectively, of the fuel required by trucks for the same tonnage. I believe the ~1% and ~3% numbers of the photo captions could be correct.

Also, do pickups and semi-trailers really achieve nearly the same fuel efficiency by weight carried? Or do we define "heavy" trucks differently?

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