However, when evaluating the environmental impacts for the full life of the building, which adds impacts due to the use and end-of-life phases to those of the cradle-to-gate, there is not much relative difference in GWP between the buildings within a given city. When evaluating the results on a cradle-to-grave basis, Figure 3 and the data show:
- In Denver, GWP varies from 58 to 62 million kg (127 to 136 million lb) CO2e, and the coefficient of variation (COV) is 2 percent.
- In Memphis, GWP varies from 45 to 46 million kg (99 to 101 million lb) CO2e, and the COV is 1 percent.
- In Miami, GWP varies from 50 to 51 million kg (110 to 112 million lb) CO2e, and the COV is less than 1 percent.
- In Phoenix, GWP varies from 44 to 46 million kg (97 to 101 million lb) CO2e, and the COV is 1 percent.
It is evident that any increased cradle-to-gate GWP is offset by reductions in the operational phase GWP for each climate zone. This is why it is important to evaluate design choices based on a full lifecycle and within the building context. In this study, there was not a significant difference in the lifecycle environmental impacts between steel, cast-in-place concrete, and precast concrete structural systems.
Viewing EPDs as one tool
Voluntary green rating systems and now federal legislation have created a tremendous need to get environmental-impact information into the hands of owners and designers. EPDs have been singled out as the tool to evaluate the sustainability of products. As the case study illustrated, making decisions based on cradle-to-gate environmental impacts does not necessarily reflect the least cradle-to-grave environmental impact. Until the time when EPDs can cover the full environmental impacts of products, caution should be taken so they are not used as the sole basis of design and procurement decisions.
Notes
1 Learn more about the Infrastructure Investment and Jobs Act (IIJA), www.congress.gov/117/plaws/publ58/PLAW-117publ58.pdf.
2 See the Inflation Reduction Act (IRA), www.congress.gov/117/bills/hr5376/BILLS-117hr5376enr.pdf.
3 Consult the Executive Order (EO) 14057. 2021, Catalyzing Clean Energy Industries and Jobs Through Federal Sustainability, www.whitehouse.gov/briefing-room/presidential-actions/2021/12/08/executive-order-on-catalyzing-clean-energy-industries-and-jobs-through-federal-sustainability.
4 Read the document by the U.S. Environmental Protection Agency (EPA), aclca.org/wp-content/uploads/2022.12.22-Interim-Determination-on-Low-Carbon-Materials-under-IRA-60503-and-60506_508.pdf.
5 Visit the Carbon Leadership Forum (CLF). Life Cycle Assessment of Buildings: A Practice Guide, carbonleadershipforum.org/lca-practice-guide.
6 Refer to the International Organization for Standardization (ISO). ISO 14040:2006, Environmental management—Lifecycle assessment—Principles and framework.
7 Refer to ISO 14044, Environmental management—Lifecycle assessment—requirements and guidelines.
8 Refer to ISO 14025:2006, Environmental labels and declarations—Type III environmental declarations.
9 Refer to ISO 21930:2017, Sustainability in buildings and civil engineering works—Core rules for environmental product declarations of construction products and services.
10 See the British-Adopted European Standard. BS-EN 15804: 2012+A2: 2019, Sustainability of construction works. Environmental product declarations. Core rules for the product category of construction products.
11 Visit the Precast/Prestressed Concrete Institute (PCI). See the Comparative Lifecycle Assessment of Precast Concrete Commercial Buildings: Overview/
Author
Emily Lorenz, PE, F-ACI, is an independent consulting engineer in the areas of lifecycle assessment (LCA), environmental product declarations (EPDs), product category rules (PCRs), green building, and sustainability. She serves as an engineer in the areas of green structures and practices, energy efficiency, thermal properties, and moisture mitigation. Lorenz actively contributes as vice-chair of the Envelope Subcommittee for the 2024 International Energy Conservation Code (IECC), participates in multiple committees including ASHRAE 90.1, ASTM E60, American Concrete Institute (ACI) sustainability, and ISO TC59\SC17\WG3. She is an expert in various technical associations, including ACI and ACI-ASCE Committees, shaping energy conservation codes and environmental product declarations (EPDs). Lorenz received her BS and MS in civil engineering (structural emphasis) from Michigan Technological University.
