The meaning of life
Flowers & Butterflies by Florian Kleinefenn
Over the past few weeks I have been working on a project that caused me to learn about life cycle assessment. Excuse me for a few minutes—I’m going to go a bit technical on you here, but I think you’ll find it worthwhile to understand a little about this.
Life cycle assessment (LCA) is a technique for evaluating the overall impact that something has on the environment (such as a building). We evaluate the impact for specific things—like greenhouse gases (global warming), acidification (acid rain), smog, and toxicity to humans. Each substance emitted is weighted for each impact—so CO2 gets a 1 for greenhouse gases but a zero for ozone depletion, acidification, and toxicity. Sulfur dioxide, on the other hand, gets a zero for greenhouse gases but a 1.2 for acidification. Dioxin gets a zero for smog but a very high number for toxicity—and so on.
To look at the life cycle impact of a building, first you figure out everything that is emitted from the construction, operation, and maintenance of the building over its lifetime—including mining the aggregate, growing the trees, transporting everything to the site, keeping the building heated or cooled, operating the lights. Then you multiply the amount emitted times the weighting factor to come up with the impact of that particular material. Do that for everything emitted and add it all up and you get the overall impact of the building.
LCA can be applied to almost anything, not just buildings—from motor vehicles to banking to the United States’ immigration policy. To do this in a comprehensive way is very time consuming and complicated. Interpreting the results is even more complicated and eventually, as seems true of everything, comes down to some biases and political choices—which is worse, cancer or global warming?
If we bring this back to the matter at hand—building with concrete—LCA is generally favorable to our cause. Although cement manufacturing has a rather high initial impact (in terms of energy used, CO2 release, mining, and transportation) the concrete it produces lasts a very long time with low maintenance so the impact is spread over many years. And at the end of its life, recycled concrete is a very useful material, unlike recycled wood.
With all the talk about green building, it would seem logical that the green points systems (LEED or Green Globes or NAHB’s guidelines) would include LCA, but at this time none of them do—at least not directly. All of the points systems do plan to bring LCA into the evaluation process in their next versions, so you’ll probably be hearing more soon. In the meantime, concrete still makes significant contributions to green building, especially in terms of its thermal mass, so we have a good story to tell that we can only hope will get better.