Study Compares Fire Resistance of Steel Cladding Coatings

In the event of an unexpected fire, the choice of exterior cladding materials can become the last line of defense for life safety. With steel-framed buildings becoming increasingly prevalent, the fire performance of cladding materials directly impacts overall building safety. This article examines three common steel cladding options—galvanized steel, polyester-coated steel, and PVC-coated steel—analyzing their performance under fire conditions to provide professional reference for project decision-making.

The Critical Role of Cladding in Steel Structures

In steel construction, cladding serves not only aesthetic and protective functions but also plays a crucial role in fire safety. Various steel cladding options offer distinct properties, durability, and fire characteristics. Understanding these fire ratings is essential for ensuring building safety, particularly when evaluating materials for single-layer applications.

Galvanized Steel Cladding: The Inherently Safe Option

Galvanized steel features a zinc coating that prevents corrosion. As this coating is metallic and contains no combustible elements, galvanized steel offers exceptional fire performance. During a fire event, it neither contributes to flame spread nor releases toxic smoke.

• Fire Rating: Non-combustible
• EN 13501-1 Reaction Class: A1
• Key Advantage: No flame spread contribution, no toxic smoke emission

Due to its superior fire performance and durability, galvanized steel is commonly used in agricultural, industrial, and indoor environments with stringent fire safety requirements.

Polyester-Coated Steel Cladding: Balancing Aesthetics and Safety

Polyester-coated steel consists of galvanized steel with an additional thin organic polyester coating (typically 25 microns). This coating provides a smooth, attractive finish along with good weather resistance. While the polyester layer may burn away during a fire, the underlying steel substrate maintains structural integrity and non-combustibility.

• Fire Rating: A1
• EN 13501-1 Reaction Class: A1
• Key Advantage: No flame spread contribution, no toxic smoke emission

This material offers an economical and visually appealing cladding solution that balances cost, durability, and safety considerations.

PVC-Coated Steel Cladding: The Durability-Fire Safety Tradeoff

PVC-coated steel (also called plastisol cladding) features a thicker PVC (polyvinyl chloride) coating (typically 200 microns) over galvanized steel. This significantly improves scratch and corrosion resistance, making it ideal for facades and roofing. However, as PVC is an organic material, it may soften or degrade at high temperatures. While the steel core remains non-combustible, the PVC coating may melt or emit smoke during a fire.

• EN 13501-1 Reaction Class: C-s3,d0
• Key Consideration: Steel core remains non-combustible, but PVC coating may produce significant smoke

Despite these fire safety considerations, PVC-coated steel remains popular for its exceptional durability and visual appeal, though caution is advised for applications near boundary walls or in public buildings with strict fire regulations.

Comparative Fire Performance Analysis

Critical Factors Affecting Fire Performance

The fire ratings mentioned apply to steel cladding used either as single-layer structures (without insulation backing) or as part of composite systems with mineral wool backing. Important specifications include:

• For profiled steel sheets, the profiled surface area must not exceed twice the covered area
• Mineral wool backing must have at least A2-s1,d0 classification with minimum 100mm thickness
• Supporting structures must achieve at least A2-s1,d0 classification

Conclusion

Selecting appropriate steel cladding requires careful consideration of fire safety requirements alongside other project specifications. While all standard steel cladding products meet rigorous quality and performance standards, their fire characteristics vary significantly. Project teams must evaluate these differences in relation to building usage, fire safety regulations, and budget constraints to make informed material selections.