Specifying architecturally exposed structural steel the right way

Stand in front of the International Spy Museum in Washington, D.C., and look up. The bold, raking red columns sloping at a dramatic 2.5:1 pitch are not a decorative skin applied over a structure. They are the building’s gravity-load carrying system—bold, expressive, and functional. That is architecturally exposed structural steel (AESS), and the moment I saw it for the first time, I understood why getting the specification right matters so much.

When structure becomes the architectural expression

AESS is structural steel intentionally left visible as part of the architectural experience of a space. Unlike standard structural steel, which is typically concealed behind fire protection and finishes, AESS is fabricated and erected to a higher standard of craftsmanship, designed and finished specifically for the location, viewing distance, and lighting conditions of each element.

At the Spy Museum, designed by RSHP with Hickok Cole as architect of record, AESS isn’t just the structure or an accent. It is the architecture. For instance, within the glass veil on the west façade, there is a monumental series of stairs and platforms constructed from custom AESS members with fully expressed connections. That feature creates a circulation sequence that is structurally honest and spatially dramatic. Every connection is visible and is part of the architectural language of the building.

The specification gap

Here is what I see too often in practice: An architect has a vision for a project where the structure is the expression; where the bones of the building are visible, honest, and elegant; and where exposed steel defines the character of a space rather than hiding behind a suspended ceiling or a layer of fire protection. The details are resolved on the drawings and ready for construction.

But when the steel arrives on-site, something is off. The surface reads differently than intended, the weld conditions aren’t what the team imagined, and the columns that were meant to feel refined look raw and industrial, leaving the entire team standing in a building, staring at steel that is already erected, wondering how it got to this point.

It got to this point because the conversation about what AESS actually means for this specific project, at this viewing distance, within this project’s budget, started too late or never happened at all. The divergence between design vision and delivered product is rarely a failure of craft. It is almost always a failure of early communication. 

AESS is fundamentally a tiered category system differentiated by architectural requirements and calibrated to technical and cost realities, where distance to view, building type, and budget should drive every specification decision. 

AESS defined across 5 categories

The American Institute of Steel Construction (AISC) Code of Standard Practice defines AESS across five categories. On this spectrum of craftsmanship, each step up represents greater surface refinement, tighter tolerances, more intensive labor, and a corresponding higher cost. Here are edited excerpts from AISC’s code explaining each category:

• AESS 1, Basic Elements, has workmanship requirements that exceed standard construction. The steel is visible but distant, positioned more than 20 feet from viewers.
• AESS 2, Feature Elements Not in Close View, allows the viewer to see the art of metalworking through geometry without finish work. The category covers elements seen at a distance greater than 20 feet but viewed by larger audiences, such as those in atria or public spaces.
• AESS 3, Feature Elements in Close View, covers AESS with geometry and basic finish work for elements seen at 20 feet or less or that visitors may touch. For acceptance, approval of a mockup is required.
• AESS 4, Showcase Elements, applies when the designer intends that form to be the only feature showing, with all of the welds ground and filled and the edges ground square and true. Like AESS 3, acceptance is based on an approved mockup.
• AESS C, Custom Elements, allows for requirements that are more or less stringent than those in any other category. Steel in the AESS C category can combine characteristics from other categories for a more economical outcome. 

Wait! Does your project even need AESS?

Before you start diving into selecting categories, it’s wise to first ask yourself: Do I really need to specify AESS on my project? This is the question I find myself asking most often, and the answer is not always yes. It is a waste of time and budget to specify highly finished steel for conditions where that level of finish will never be visible. Standard structural steel, properly primed and painted, can be entirely appropriate and more cost-effective when the viewing distance simply doesn’t justify the investment.

At the CITYPARK soccer stadium in St. Louis, project specifications initially called for an AESS designation until mockups were built and the team stood in front of actual fabricated steel and asked honestly: Does this meet the design intent? Is this what we wanted? The answer revealed that the desired aesthetic could be achieved without AESS and for less cost.

At the Truist Leadership Institute in Greensboro, N.C., the answer was different but the process was the same. Working closely with the steel fabricator, the design team developed two custom AESS categories, a more refined finish where the steel would be most visible and a less refined finish where it would not, ensuring the tactile quality of every weld condition matched the design intent precisely where it mattered.

The conversation you cannot skip

For AESS 3 and 4, mockups are required under AISC’s Code of Standard Practice. When a mockup is constructed, standard practice is for the project team—architect, structural engineer, fabricator, general contractor, and erector—to assemble, examine the mockup, and ask honestly: Does this meet the design intent? Is this what we wanted?

During the Spy Museum project, the team reviewed a full-scale mockup of the expressed column connection at the fabricator’s shop before a single production piece was cut, aligning everyone on surface articulation, coating quality, and finish tolerance. The result was a building where the steel arrived on site as designed.

By engaging your fabricator early, building the mockup, and having the conversation before fabrication begins, you can help ensure that the project team is in alignment, laying the groundwork for a successful outcome. 

Experience the difference for yourself at the 2026 AIA Conference on Architecture & Design

On June 11 and 12, AISC will feature real-world AESS samples (categories 1-4) in exhibit booth 4023. Examine the samples up close under consistent lighting conditions and discover the differences between the categories by touching them. 

AESS resources and project case studies are available at aisc.org/aess. For a deeper understanding of the art and science of AESS, watch “Architecturally Exposed: Understanding the Art and Science of Architecturally Exposed Structural Steel” on YouTube.

Nima Balasubramanian, AIA, NOMA, is the director of architecture at the American Institute of Steel Construction. 

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