During a recent ANSI Green Globes conference call, a fellow committee member suggested that embodied energy of building materials deserves greater attention in green building rating systems, now that buildings are becoming more energy-efficient. A Green Building Advisor article “All About Embodied Energy” by Martin Holladay was offered in support of this idea. Holladay begins the article by explaining that, until recently, embodied energy of building materials wasn’t worth considering because the amount of energy used in making building materials was dwarfed by the energy used to operate a building over its lifetime (between 90 to 95 percent according to a paper by I. Sartori and A.G. Hestnes “Energy Use In The Life Cycle Of Conventional and Low-Energy Buildings.”) Holladay wonders whether or not this 20-year-old rule of thumb applies today.
It’s simple to calculate the relationship between a buildings operational energy and the energy that was used to make its materials. You just need to know how much energy the building uses each year, how long the building will be around, and how much energy was used to make all of the materials that went into the building—including materials that need to be replaced over the life of the building. Holladay provides multiple examples of folks that have attempted the calculation for all kinds of building types of all ages all over the world, arriving at an overall value of building materials energy to operational energy anywhere from 2 to 75 percent. Why the huge spread between these numbers? Lots of reasons, on both sides of the equation. On the materials side, it is very difficult to obtain accurate, trustworthy embodied energy values. Tracy Mumma, in her article “Reducing the Embodied Energy of Buildings,” explains: