Fire Boarding & Encasement Systems | Selecting the Right Board for 30, 60, 90 & 120 Minutes
The Steel Does Not Fail — It Softens
Structural steel rarely burns.
It loses strength.
At approximately 550°C, loadbearing capacity can reduce by around 50%. Above that, deflection accelerates. In fire, time is measured not in flame height but in temperature rise within the steel section.
Fire boarding exists to delay that rise.
Encasement systems are designed to insulate steel members so that they remain below their critical temperature for a defined resistance period — 30, 60, 90, or 120 minutes.
The selection of the correct board system is therefore not aesthetic. It is mathematical.
Understanding Resistance Ratings
Fire resistance ratings express time — but they are rooted in test evidence.
Structural protection systems are tested to standards such as:
• BS 476
• EN 13381
Testing measures:
• Loadbearing capacity (R)
• Integrity (E)
• Insulation (I)
For structural steel, the critical measure is typically the time taken for steel temperature to reach a specified limit under furnace conditions.
Board thickness, density, fixing spacing, and joint treatment are all defined by the test.
Resistance is not a generic property of a board.
It is a property of a tested assembly.
The Section Factor: The Quiet Variable
Before selecting any board system, the steel itself must be understood.
The section factor (Hp/A) — the ratio of heated perimeter to cross-sectional area — determines how quickly a steel member heats up.
• Slim sections heat rapidly.
• Heavy sections heat slowly.
The higher the section factor, the greater the thickness of protection required.
Board selection therefore begins not with the catalogue, but with structural drawings and fire strategy documentation.
Board System Types
Fire protective boards fall broadly into three categories:
1. Calcium Silicate Boards
• High density
• Mechanically strong
• Suitable for exposed conditions
• Common for 60–120 minute ratings
These boards provide robust, impact-resistant encasement and are often used in plant rooms or service areas where durability matters.
2. Gypsum-Based Fire Boards
• Lighter weight
• Typically used within drylining systems
• Suitable for lower resistance periods or protected locations
Performance depends heavily on joint treatment and correct screw spacing.
3. Vermiculite or Cementitious Boards
• Good thermal insulation properties
• Frequently used for steel column encasement
• Available in multi-layer configurations for higher ratings
These systems rely on correct layering and staggered joints to maintain integrity.
Selecting for 30, 60, 90, and 120 Minutes
Resistance selection is driven by fire strategy and building use.
30 Minutes
Often used in smaller buildings or specific elements with reduced risk.
• Minimal board thickness
• Single-layer systems
• Careful attention to joint sealing
Precision remains essential; lower rating does not mean relaxed standards.
60 Minutes
Common in commercial and residential developments.
• Increased board thickness
• Defined screw patterns and edge distances
• Joint reinforcement often required
This rating forms the baseline in many compartmentation strategies.
90–120 Minutes
Required in higher-risk or multi-storey buildings.
• Multi-layer board systems
• Staggered joints
• Defined insulation infill
• Enhanced fixing density
These systems demand careful sequencing and inspection before closure.
Under the Building Safety Act, higher-risk buildings require rigorous documentation of installation and inspection.
Fixing, Joint Treatment, and Edge Conditions
Board performance is governed as much by fixing detail as by material thickness.
Test reports define:
• Screw type and spacing
• Steel stud or bracket configuration
• Joint sealing compound
• Edge support requirements
• Maximum unsupported spans
Common site failures include:
• Incorrect screw spacing
• Gaps at board edges
• Unsealed joints
• Incomplete boxing around beam flanges
Each deviation alters fire performance.
Encasement must form a complete thermal envelope around the steel. Partial protection is not protection.
Moisture, Impact, and Environmental Conditions
Board selection must also consider environment:
• Is the area prone to moisture?
• Is impact resistance required?
• Will the board remain exposed or be overclad?
Calcium silicate boards may be preferable in damp or plant room environments. Lightweight gypsum boards may be unsuitable without protection.
Performance under fire is primary — but durability in service preserves that performance.
Integration with Other Systems
Fire boarding does not operate in isolation.
Encasement systems must integrate with:
• Fire stopping at service penetrations
• Intumescent coatings (where hybrid systems are used)
• Ceiling and partition interfaces
• Structural movement joints
Poor coordination at these junctions creates weak points.
The board may be correct; the interface may not.
Inspection and Evidence
Every encased column or beam must be verifiable before concealment.
Good practice includes:
• Pre-installation checks of steel condition
• Photographic records of section factor calculations
• Installation images before joint sealing
• Final inspection and labelling
Accredited installers working to third-party schemes provide traceable evidence that the installed system matches tested detail.
Without this record, resistance cannot be proven.
Why Substitution Fails
Replacing one board with another of similar thickness does not guarantee equivalent performance.
Density, composition, thermal conductivity, and joint behaviour differ between manufacturers. Only systems tested and classified under the relevant standard are valid.
“Like for like” is not a technical category.
Conclusion — Resistance Is Engineered, Not Assumed
Fire boarding and encasement appear simple: boards fixed around steel, joints sealed, edges aligned.
In reality, each installation represents a calculation translated into material form.
Select the wrong board, and the steel reaches critical temperature too soon.
Install it incorrectly, and the test result becomes irrelevant.
Fire resistance is not an aspiration. It is a measured outcome, achieved through tested systems, correct section factor assessment, disciplined installation, and documented verification.
Steel will soften when heated.
Board systems exist to delay that moment.
The responsibility lies in choosing — and installing — the correct one.