Infrastructure Outlook: EPD: Green Goals with HSS
There’s a growing push for the building industry to reduce embodied carbon and greenhouse-gas emissions to slow global-warming effects. This is evident in the passing of the Buy Clean California Act (BCCA) requiring any projects entering contracts with the state of California use construction materials that fall under maximum embodied carbon thresholds. Those who don’t work in California may have breathed a sigh of relief, but this legislation has gained momentum in other states and potentially on the federal level. Therefore, for any designers or material suppliers, it’s prudent to learn more about embodied carbon in building materials and how this will impact projects.
Although this column focuses on steel Hollow Structural Sections (HSS), this information can be extrapolated to other materials. I recommend reading “Achieving Green Goals with HSS,” an article published by the Steel Tube Institute (STI) that provides comprehensive information on environmental impacts, definitions and development of threshold numbers (bit.ly/3xtvHWm).
The Basics of EPDs
The BCCA limits the amount of embodied carbon allowed in building materials in public projects. Embodied carbon thresholds per BCCA are reported in an Environmental Product Declaration (EPD), a third-party-verified document that summarizes environmental impacts of a building material product from a lifecycle assessment. EPDs are likened to nutrition labels for a food product, conveying the environmental health of a building material.
One way EPDs measure environmental impact is by reporting Global Warming Potential (GWP) for a material. The GWP number for steel is a measure of the embodied carbon expended to manufacture the steel product. The lower the GWP number, the lower the embodied carbon to manufacture the product, leading to less potential for global warming.
1. What’s the maximum GWP threshold allowed per BCCA? STI, AISC, CRSI and AISI developed a “Quick Guide to BCCA’s Steel Provisions” (bit.ly/3CzuDnA). This document summarizes maximum GWP values required by BCCA, which also are listed in Table 1. The left column represents the maximum GWP allowed at mill gate prior to fabrication, and the right column represents the GWP threshold allowed after fabrication.
2. Where can we find GWP numbers for steel used on our projects? The actual GWP values for steel used on projects will be found in facility-specific EPDs published by steel mills. BCCA requires facility-specific EPDs for HSS. Since designers may not know during design which steel mills will supply steel, it’s difficult to confirm GWP numbers based on facility-specific EPDs. However, steel suppliers can obtain this information from service centers or steel mills during the procurement phase. STI developed an industry-wide HSS EPD for LEED that also can serve as a reference for designers or steel suppliers. Note that the STI EPDs are industry-average values, not facility-specific as required by BCCA. Table 2 is an excerpt from the STI industry-average EPD for Fabricated HSS (2016).
For example, compare the STI industry-average HSS EPD with the maximum GWP threshold per BCCA. Since the 2016 STI EPD reports fabricated HSS per Table 2, we compare this to fabricated GWP thresholds per BCCA in Table 1.
Industry-average fabricated HSS GWP per STI/AISC EPD = 2.39 tons C02 eq / tons of steel is less than fabricated GWP Threshold per BCCA = 3.19 tons C02 eq / tons.
The 2016 STI EPD industry-average HSS GWP is within acceptable thresholds of BCCA. A similar evaluation would be performed for facility-specific EPDs received by mills and/or service centers to confirm BCCA compliance.
It helps to understand how GWP values are developed to understand the direction HSS is headed. There are two primary methods to manufacture steel coil used to produce HSS: Blast Oxygen Furnace (BOF) and Electric Arc Furnace (EAF). Historically, HSS was produced from coils manufactured using the old open-hearth BOF method. The EAF method uses recycled steel scrap to manufacture steel coil and utilizes a cleaner electric grid, resulting in less embodied carbon. In recent years, there has been an increase in HSS production using EAF-manufactured coil domestically in the United States, and GWP values are expected to decrease from the 2016 values.
Two major updates occurred surrounding embodied carbon in building materials:
1. BCCA requirements for steel purchased for State of California projects were originally effective as of July 1, 2021. This date has been delayed until July 1, 2022.
2. HSS producers developed new facility-specific and industry-wide EPDs and GWP numbers in July 2021. At the time of this column, third-party verification was completed on the industry-wide EPD. The new industry-wide HSS GWP value is 1.71 tons C02eq/tons based on unfabricated HSS, confirming a decrease in GWP values from the 2016 industry-wide EPD. Facility-specific EPDs are under verification. Please check the STI website at www.steeltubeinstitute.org for release of new HSS EPDs.
Expanding on No. 2, the new EPD now uses a North American GWP number for the LCA coil data—not global—indicating a shift toward EAF-produced coils for HSS. Also, there are ongoing efforts to increase efficiency in the electric grid powering EAF manufacturing. The electric grid also is becoming more energy-efficient and fossil-free. These reasons contributed to a decrease in GWP for HSS.
What Designers Need to Know
BCCA is a change to the material procurement process, not necessarily the design process. However, designers interested in lowering embodied carbon can keep a few things in mind.
When selecting materials for a project, we can’t only compare raw GWP numbers in EPDs between different materials (steel to concrete) or even within steel materials (WF to HSS). GWP numbers are based on the material’s unit of measurement (e.g, tons for steel, etc.). The quantity of material used to resist the same loading will vary due to strength and stiffness of materials.
To compare apples to apples, the structure should be analyzed and designed in each material separately to result in a quantity for each material. Multiplying each material quantity by its corresponding GWP number would result in a final embodied carbon level for each material. We then can compare these carbon levels more accurately across materials.