Sustainability Starts at the Top

The built environment accounts for about a third of the greenhouse gas emissions that contribute to climate change. As operational emissions from buildings in the United States—such as those produced by the energy that building systems use—have generally decreased with time, the building industry has turned more attention to embodied carbon reduction, which refers to the emissions from the production of construction products. The good news is that developers and owners can do a lot to set and meet their project’s embodied carbon goals, and structural steel can help them.

How can structural steel help? Domestic steel is sustainable without a cost premium. Steel has significant advantages for recycling and possible reuse at the end of a building’s life. The adaptability of steel structures is an advantage for the overall lifespan of a building, whether it is new construction or adaptive reuse. All U.S.-based steel mills produce facility-specific EPDs that clearly explain the carbon footprint associated with their production.

This article is an abridged version of AISC’s Steel and Sustainability: An Owner’s Guide, which was co-authored by AISC and Magnusson Klemencic Associates. It expands on these questions and considerations and explains how steel is a sustainability winner. Access the full document with case studies, appendices, and more for free at www.aisc.org/sustainability-toolbox.

The domestic iron and steel industry accounts for 1.9% of all U.S. energy-related CO2 emissions. However, structural steel (which makes up a building’s beams, columns, plates, etc.) accounts for only 8.5% of the U.S. market, meaning structural steel’s share of emissions is somewhere around 0.16%. On top of this low upfront market impact, steel also has a distinct advantage over other materials in its ability to be reused or recycled. Steel can be repeatedly recycled by melting and recasting without losing its fundamental mechanical properties.
A basic understanding of how steel is made is helpful for understanding the carbon footprint of steel. The two main methods of steelmaking use a blast furnace and basic oxygen furnace (BF-BOF) or an electric arc furnace (EAF).

Blast furnace and basic oxygen furnace (BF-BOF): An extractive approach that uses mined raw materials as its primary input and predominantly coal power and natural gas as its fuel source.

Electric arc furnace (EAF): A circular approach that uses recycled scrap as the primary source of input and electricity as its source.

Approximately 70% of all steel production in the U.S. comes from EAF, while the remaining 30% comes from BF-BOF. All hot-rolled sections are made in EAFs. In other countries such as China, India, and Russia, BOF remains the predominant form of steelmaking, which is why environmentally conscious owners and developers should avoid using foreign steel.

The overall structural system selection will have a significant impact on the potential embodied carbon associated with the building. Structural steel is the ideal choice when considering sustainability, based on the following benefits:

Inherently sustainable: All structural hot-rolled sections produced in the U.S. are made with EAF production, which, as mentioned above, uses an average of 92% recycled content and is 100% recyclable at the end of life. Domestically produced structural steel is already some of the cleanest steel in the world and doesn’t cost extra.

Transparency: All U.S. structural steel mills produce facility-specific EPDs that clearly explain the carbon footprint associated with their steel production, including a complete evaluation of the supply chain. This is the most accurate and transparent representation of the environmental impact of the specific facility when compared to an industry average evaluation, and the steel industry can boast 100% EPD coverage. No other construction material comes close to matching the level of data transparency and availability.

Adaptability: A more adaptable structure will lead to a longer service life for a given building and potentially higher resale value. Structural steel has the distinct advantage of significant adaptability to incorporate future building modifications, such as the addition of new floor openings, an increase in floor loading capacity, or completely repurposing a building. Compared to other structural systems where a more disruptive retrofit may be required or where retrofit is impractical, a structural steel building can achieve a longer service life and avoid the costly environmental impacts of replacing a building.

Resilience: Steel structures are non-combustible, capable of handling unexpected extreme loads in both compression and tension, not subject to water damage, and durable, therefore offering a resilience advantage over other materials. This advantage can be realized as a lower risk for insurance during construction and for the entirety of the building’s life.

End-of-life benefits: Structural steel is 100% recyclable, making it a completely circular material. Additionally, deconstruction and reuse are feasible strategies that can offset the embodied carbon associated with new construction.

Once a structural steel system is selected, the following sections describe options you can discuss with your design team that can further impact the embodied carbon of construction.

While many factors drive building optimization, the sustainability of a steel structure is proportional to the quantity of steel required. The steel quantity is impacted by decisions that must be made by the owner and design team on the following:

Where appropriate, building owners should also encourage the design team to explore innovative strategies, including:

Hybrid systems with steel framing and mass timber flooring. Recent innovations with mass timber products such as CLT have been incorporated with steel framing to result in an efficient and lower carbon assembly compared to traditional slab on composite deck construction.
Incorporating salvaged materials. Constructing with salvaged materials is a highly effective way to reduce embodied carbon.

High-strength steel. High-strength steel generally has the same carbon footprint as typical steel grades, resulting in a direct embodied carbon reduction proportional to the steel weight saved using high-strength steel.

Performance-based fire design. Performance-based fire design is a modern approach to ensure fire safety based on achieving safety outcomes through an in-depth analysis of fire risks, building performance, and safety which can help achieve a significant reduction or elimination of fireproofing of the structure, thus reducing overall embodied carbon for the building.

While many of these example studies are presented in isolation, the combined effects need to be evaluated on a project-specific basis. For example, the use of a hybrid steel-timber deck along with a larger column grid may result in overall savings in embodied carbon when evaluated holistically with foundation impacts.

Embodied carbon should be evaluated at major design and construction milestones to understand the project trajectory. This may include comparing to industry baselines in order to benchmark the building or earn points for rating systems such as LEED.

As design development progresses, the uncertainty in the building material quantities reduces, and eventually, quantities measured and purchased by the contractor can be used. Likewise, the carbon intensity of the structural materials can be challenging to estimate early in the design, given the variability in manufacturing processes. Therefore, industry-average embodied carbon values should be applied at the beginning of the design. (The webpage www.aisc.org/epd has AISC industry-average EPDs). As the design is completed and steel is procured, project-specific information should be provided and applied to the LCA.

The primary types of EPDs in the structural steel industry are industry-wide, which contain the average data that can be used early in the design process, and mill-specific, which are specific to the production facility and can be used during design refinement.

Care should be taken when comparing industry-wide and mill-specific EPDs, as many of these data sets are not directly comparable due to differences in background datasets used, age of data, uncertainty assumptions, LCA methodologies, PCR versions, and other variables. Overall, the structural steel industry is very transparent with its environmental data relative to other construction materials and has nearly 100% coverage of that environmental data for all structural steel products.

Procurement is another significant opportunity to impact the embodied carbon of a building. Embodied carbon can be used as another basis for bid evaluation, in conjunction with typical variables like cost and schedule. Some strategies include:

Owners and project teams should refer to the Specification Strategies for Structural Steel Embodied Carbon Reduction document (available at www.aisc.org/sustainability-toolbox) for commentary and sample specification language.

Projects have also successfully used bidding alternatives to provide tiers of carbon reduction with various ranges of cost impacts. For example, the primary bidding instructions may be to bid based on “business as usual” with supporting EPDs. Then, an alternative for maximum carbon reduction could be requested that may have an associated cost premium.

Building tenants are increasingly seeking high-performing sustainable buildings, and owners should keep the sustainability considerations in this article top of mind. When owners consider and prioritize these factors, structural steel will often prove to be an attractive material choice and help compliance with local or state regulations, such as Buy Clean legislation. No matter the building material, sustainability decisions begin long before any contracts are signed or design choices or made—and the Steel and Sustainability: An Owner’s Guide, which is part of the Owner’s Toolkit (download at www.aisc.org/sustainability-toolbox), can guide the decision-making. ■

About the Author

Kevin Kuntz (kkuntz@mka.com) is an associate and Ian McFarlane (imcfarlane@mka.com) is a senior principal, both at Magnusson Klemencic Associates. Jonathan Tavarez (tavarez@aisc.org) is a structural steel specialist with AISC.