6 Strategies for specifying structural steel with low embodied carbon

Specifiers have a powerful new resource to help them use low-embodied-carbon structural steel on their projects.

The American Institute of Steel Construction (AISC)’s new publication, Specification Strategies for Embodied Carbon Reduction, summarizes the latest and most relevant approaches for procuring structural steel with low embodied carbon. Found on AISC's website, the publication presents six strategies along with extensive commentary, ratings, and, of course, sample specification language. Many groups contributed to the content, including AISC’s Sustainability Committee, the Resources Subgroup of the SEI Sustainability Committee, the Specification Working Group of the NCSEA National Sustainable Design Committee, and a consulting architect specializing in specification writing.

Don’t know what embodied carbon is? In construction materials, embodied carbon consists of the greenhouse gas (GHG) emissions associated with the creation, use, and disposal of those materials over the entire life cycle of a building. The largest sources of embodied carbon associated with steel are the GHG emissions that occur during the iron- and steel-making stages.

The following are descriptions of each strategy and their intended use. You can find more information about sustainable steel on AISC's sustainability page. 

Strategy 1: Environmental product declaration (EPD) disclosures

Requiring an EPD disclosure is an easy way to ensure that you’re working with suppliers who are as committed to sustainability as you are. It also ensures that when it’s time to calculate credits for various green building rating systems, the documentation you need will be right at your fingertips. Requiring EPDs has the added benefit of underscoring that the market cares about having current, transparent, and accurate documentation. 

AISC recommends all steel construction specifications include this requirement. It is easily to implement and is unlikely to have a substantive impact on either project cost or project schedule.

Strategy 2: Sustainable fabrication

It’s worth engaging with sustainable steel fabricators to promote lean and sustainable practices. How they run their operations, from material procurement all the way to the jobsite, makes a difference. Requiring documentation about a fabricator’s sustainability practices is another way of ensuring that your entire project team is committed to the same goals.

Here’s a shortcut: AISC offers a sustainability partner program specifically for steel fabricators. The program provides best practices and helps them streamline their operations and the resulting environmental impact. Any fabricator participating in the program has already met the requirements laid out in this specification language. You can find a list of them on AISC's partners page. 

Strategy 3: Domestic sourcing

Simply choosing domestic steel can cut its environmental footprint in half. The American structural steel industry’s average embodied carbon intensity is way ahead of the global average—by some 40% for hot-rolled sections, in fact—and buying steel made in America eliminates the pollution associated with transcontinental transportation.

While it’s possible for some foreign sources to have carbon intensities generally on par with the U.S., it’s necessary to assess the environmental impacts of global transportation and to evaluate whether foreign carbon intensity reporting is meeting the same U.S. standard of quality. Regardless, foreign-sourced steel must always include certification from a domestic importer that material properties are correct and verifiable.

Note that larger shapes, typically above 300 lbs./ft., may only be available from a limited number of domestic suppliers.

Strategy 4: Electric arc furnace sourcing

How your project’s steel is made has a huge impact on its sustainability. There are two ways to do it. Some products are still made with the traditional method of creating pig iron, then operating a basic oxygen furnace (BOF) to make steel. Other products are made with scrap and electricity in an electric arc furnace (EAF).

Because EAF production uses scrap as their primary feedstock, EAF steel routinely boasts recycled content levels of 90% or more. Globally, EAF steel production is on average 75% less carbon intensive than the traditional method, largely because using recycled scrap as feedstock for new steel has nearly no environmental impact.

Except for domestic wide-flange steel, which is always made in an EAF, the marketplace offers both EAF- and BOF-produced versions of many steel products. This is where specification can make a huge difference. For products like steel plate that have not been substantially reformed between the mill and the jobsite, verifying the production process is straightforward. However, manufacturers of products like open-web steel joists, deck, and hollow structural sections would have to investigate and disclose how their source material is made.

Strategy 5: Global warming potential (GWP) limits

Published GWP values are a reasonable indicator of a steel product’s embodied carbon. GWP limits are commonly established at industry average levels, but AISC suggests a more lenient approach—specifically, setting limits at 125% of industry average levels.

The published table for this strategy, which provides cradle-to-mill-gate and cradle-to-manufacturer-gate GWP limits, as appropriate, assumes a 125% level. Note that it explicitly excludes the impact of individual downstream processes (such as shot-blasting, custom bending/rolling, castellation, fabrication, and coatings). For more information, download Buy Clean guidance from AISC.

Strategy 6: Recycled content minimums

There is a correlation between higher recycled content levels and lower embodied carbon intensity, but using one as a proxy for the other may not be fully accurate for a specific product. Mill reporting of recycled content reflects annual averages, not the characteristics of a specific steel product from a specific production heat. The recycled content of steel products fluctuates from melt to melt, so recycled content letters from mills, which reflect annual averages, may not sufficiently represent the recycled content of an individual product.

As some green building rating system credits still address the recycled content of materials, this strategy does aid in the convenient retrieval of documents necessary for those credits. AISC does not recommend this approach simply because there are more effective alternatives. It is, however, common among sustainability strategies in the marketplace.

Conclusion

For each strategy you adopt from Specification Strategies for Structural Steel Embodied Carbon Reduction, your specifications will contribute to signals that tell the steel industry that embodied carbon reduction is a valued performance metric, which incentivizes broad steelmaking decarbonization. Companies exist to compete for your business and deliver products the market wants. You are the market. It’s your job to signal your values. AISC’s Specification Strategies for Structural Steel Embodied Carbon Reduction empowers you to do so. Open AISC’s sustainability toolbox to learn more.

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