Architecturally Exposed Structural Steel (AESS): Maintaining Design While Meeting Fire Code

Architecturally Exposed Structural Steel (AESS) has become one of the defining features of modern architecture. From soaring airport terminals and university atriums to healthcare facilities, museums, and corporate headquarters, exposed structural steel creates clean lines, open spaces and a sense of transparency that many owners and designers crave.

However, exposing structural steel introduces an important challenge.

While architects want the beauty of visible steel, building codes often require those same structural members to achieve a 2-, 3-, or 4-hour fire rating.  Finding a solution that satisfies both aesthetics and life safety requires thoughtful planning early in the design process.

Fortunately, architects have several fire protection options available.  Understanding the advantages and limitations of each helps ensure the finished building meets both the architectural vision and the projects fire-resistance requirements.

What exactly is AESS?

AESS refers to structural steel members intentionally left visible as part of the finished architectural design rather than concealed behind ceilings, walls, or other finishes.

Unlike standard structural steel, AESS typically requires a higher level of craftsmanship including:

• Cleaner welds
• Smoother surface finishes
• More refined connections
• Improved alignment and fit
• Consistent appearance

Key Takeaway:  AESS is more than exposed steel – it is structural steel designed to be part of the architecture.  


Why Fire Protection Becomes More Challenging

Steel is strong, durable and versatile but during a fire, it loses strength as temperatures rise.  Building codes therefore require many structural members to achieve a specified fire-resistance rating.

Traditional fireproofing methods often work well for concealed structural steel, but once steel becomes part of the finished architecture, appearance can seem as important as code compliance.  The challenge shifts from simply protecting the steel to protecting it without compromising the design.

Common Fire Protection Options for AESS

• Spray Applied Fireproofing (SFRM): SFRM is widely used throughout commercial construction and is often the most economical solution for concealed structural steel
• Advantages:
• Proven fire protection
• Lower material cost
• Widely available
• Disadvantages:
• Rough, textured finish
• On site applications lead to additional waste
• Can be easily damaged onsite if left exposed
• Onsite inspection is required
• Intumescent Fire-Resistive Coatings: Intumescent coatings provide a thin, paint-like finish that expands during a fire to protect the structural steel.
• Advantages:
• Preserves the shape of the steel
• Architectural appearance can be favorable
• Thin coatings keep steel from appearing bulky
• Disadvantages:
• Onsite Inspection is Required
• Designers note a “snakeskin or orange peel” look of the finished material
• Application requires certain weather conditions, surface preparation and additional trades
• Prefabricated Fire Rated Column Assemblies (Fire Trol): these assemblies arrive at the jobsite with the fireproofing already incorporated into a UL certified system.  For projects where both appearance and schedule are priorities, prefabricated assemblies can help simplify installation while maintaining the desired architectural aesthetic.
• Advantages: 
• Factory controlled quality
• Smooth architectural finish
• Reduced field applied fireproofing
• Consistent appearance
• Available with 2-, 3-, or 4-hour fire rating

Why Early Coordination Matters

Many challenges associated with exposed structural steel can be avoided through early collaboration.  When designers and fabricators coordinate during schematic design, they can address:

• Fire resistance requirements
• Connection details
• Architectural finishes
• Member sizes
• Construction sequencing
• Installation logistics

Waiting until later in the project often results in redesigns, RFIs and field modifications that increase both cost and construction time.  By selecting the appropriate fire protection system early, architects can preserve the visual impact of exposed structural steel while meeting code requirements and supporting efficient construction.

Remember these key considerations ~ evaluating them together leads to better project outcomes:

1. Required fire rating
2. Desired appearance
3. Long term durability of fire rating material
4. Construction schedule
5. Maintenance expectations
6. Budget