Read the related story, "Concrete, Steel, or Wood: Searching for Zero-Net-Carbon Structural Materials."

Measuring embodied carbon is complicated. It requires tracking materials through fantastically elaborate manufacturing supply chains. With so many variables, “the precision of a great deal of ecodata is low,” writes British materials scientist Michael Ashby in his book Materials and the Environment (Butterworth-Heinemann, 2009).

The good news is that more manufacturers and industry groups are publishing environmental impact data on their products, often with third-party verification. Even better, new digital tools make it possible to compare life cycle analyses (LCAs) and Environmental Product Declarations (EPDs) during the course of project development. Examples include:

Sample Environmental Product Declaration (EPD) template
Source: EPD International Sample Environmental Product Declaration (EPD) template

The change is welcome. EPDs to date have proven woefully incomparable. Though all EPDs conform to the same ISO standard, each one defines its own product category rules and presents its data in a different format. Many EPDs even come with a disclaimer renouncing their comparability. For example, you may be able to search for products with the lowest global warming potential, but the underlying data may reflect only a portion a product’s life cycle: the pre-construction phase (known as “cradle to gate”); a limited portion of the manufacturing phase (“gate to gate”); or the entire life cycle (“cradle to grave”), including maintenance and end of life.

The most useful EPDs are not only verified by a third party, such as UL, but also include data on specific manufacturers and factories. Industry-average data may conceal wide swings in the carbon footprints of different manufacturers and regional supply chains.

The takeaway? Always ask for cradle to grave EPDs from manufacturers and leverage tools that allow for comparability.

This article appeared in the January 2020 issue of ARCHITECT, with the headline “Making Sense of the Metrics.” With additional reporting by Katharine Keane on the list of resources and tools.