When sustainable building was a new concept, materials were generally chosen based upon a single attribute—recycled content, for example, or low VOC emissions. Now it has become clear that trade-offs are inherent with this method. For example, a material that contains a large percentage of recycled content may also be a material that has a high embodied energy.
Life-cycle assessment (LCA), a comprehensive method used to assess and quantify the environmental impact of a product or process over its entire life cycle, is becoming a common way to make fair comparisons between materials or systems. More and more manufacturers are providing environmental product declarations (EPDs), labels that contain a summary of LCA results. But LCA and EPDs are complex, with nuances that designers must be aware of in order to use them effectively.
LCA and EPDs are greatly influenced by the system boundary chosen. ISO 14044 allows the LCA practitioner to consider any boundary, and include or exclude any process, as long as these items are all explained in the LCA report. For manufacturers of products like concrete, an EPD for a unit volume of concrete can account for all the energy, materials, and emissions related to the material’s manufacture. But there are infinite possibilities for the use of that concrete once it leaves the plant gate. It could be used as a sidewalk, in a wall, as a bridge component, or many other applications. For this reason, manufacturers can account for all the environmental impacts from the cradle to the gate, but it is very difficult to account for the environmental impacts related to the use and end-of-life phases in an EPD.
Nevertheless, the most representative accounting of a product’s environmental impact covers its full life: extracting raw materials from nature, transformation or manufacturing of these raw materials into a product, the product use, and end-of-life scenarios such as recycling or disposal. This is considered a cradle-to-grave study and it is particularly important for building materials, since buildings have the greatest environmental impact during their use phase. In fact, studies of buildings in some conditions have shown as much as 95 percent of their life-cycle greenhouse gas emissions occur during the operations phase.
Examining cradle-to-grave effects can yield significant results. For concrete, while it is often impossible for manufacturers to anticipate the end uses of their product, it is typically during the use phase that the material contributes greatly to sustainability (providing thermal mass, low maintenance, and durability in even the most severe environmental conditions).
Properly utilized, LCAs can afford insight into the full impact of various building materials and create a more level playing field for comparing competing products. With programs such as the Architecture 2030 Challenge encouraging designers to find solutions that reduce energy consumption and greenhouse gas emissions, there is no better time than the present to more fully leverage cradle-to-grave LCAs.