Encasement Techniques for Fire-Proofing Steel in Complex Structures
When it comes to protecting structural steel in complex buildings—be they high-rise towers, sprawling transport hubs, or architecturally intricate cultural spaces—encasement remains one of the most reliable forms of passive fire protection. It’s not glamorous, and it often disappears behind the finished aesthetic. But when fire strikes, it’s these concealed defences that keep everything standing.
In this post, we’ll explore what fire-proof encasement involves, why it’s crucial in complex designs, and which materials and techniques are most effective in meeting UK fire safety regulations.
Why Fire-Proof Encasement Matters
Steel is strong, versatile, and essential to modern architecture—but it’s not immune to fire. At around 550°C, structural steel begins to lose its load-bearing capacity. In complex structures where load paths are non-linear or asymmetrical, any failure can quickly become catastrophic.
Encasing steel elements in fire-resistant materials delays heat transfer, maintaining structural stability and allowing safe evacuation and fire service intervention.
Common Encasement Materials
Several materials are used to encase and protect steel, each with their own strengths depending on the environment and aesthetic demands:
🟩 Gypsum-Based Boards
• Lightweight and easy to cut to size
• Often used in commercial interiors
• Typically provide 30–120 minutes of protection
🟫 Calcium Silicate Boards
• Denser and more robust than gypsum
• Ideal for areas exposed to moisture or mechanical impact
• Up to 240 minutes of fire resistance
🟨 Cementitious Sprays
• Ideal for irregular steel profiles or hard-to-reach areas
• Quick to apply on large surfaces
• May require sealing or protection from physical damage
🟥 Intumescent Boarding Systems
• Combine thermal insulation with clean finish
• Some allow decorative overboarding
• Useful where aesthetics and fire protection must coexist
Techniques for Complex Structures
Modern buildings aren’t boxes. Their curves, overhangs, integrated services, and exposed steel mean one-size-fits-all solutions won’t cut it. The following techniques are crucial for effective encasement:
• Pre-Installation Coordination: Early involvement with architects and M&E teams ensures buildability and continuity of fire compartments.
• Precision Cutting & Framing: Custom boards are cut and framed to match complex geometries—every flange, junction, and bolt head accounted for.
• Integrated Detailing: Junctions with walls, ceilings, and services are sealed to maintain compartmentation and prevent smoke spread.
• Multi-Layer Systems: Where high protection ratings are needed, encasements are built up in layers with staggered joints to eliminate weak points.
Compliance with UK Regulations
Encasement systems must be tested to BS 476: Part 21 or EN 13381-4, depending on the approach. Load-bearing integrity and insulation periods (e.g. 60, 90, 120 minutes) are determined by structural calculations and building risk profiles.
It’s also essential to work with certified installers who understand the nuances of fire strategy, compartmentation, and product compatibility. Mistakes aren’t just costly—they’re dangerous.
Final Thoughts
In complex buildings, fire-proofing steel is not just about ticking a box—it’s about designing for resilience, safety, and longevity. The right encasement technique ensures the building performs as it was intended to, even under the harshest conditions.
At JW Simpkin, we specialise in bespoke passive fire protection solutions, including board encasement, to meet the most demanding structural and aesthetic requirements. If you’re working on a complex project, get in touch—we’ll help you keep the fire where it belongs: out.