Fire Resistance of Magnesium Oxide Sheathing Board Explained

Magnesium Oxide (MgO) sheathing boards are becoming increasingly popular in construction due to their exceptional fire-resistant properties. This article explores why MgO boards outperform traditional building materials in fire resistance, their testing standards, practical applications, and how they compare to alternatives like gypsum and cement boards.

Fire Resistance of Magnesium Oxide Sheathing Board

Magnesium Oxide boards offer exceptional fire resistance due to their unique chemical composition and physical properties. Unlike traditional wood-based sheathing materials, MgO boards won't contribute to fire spread and can actually help contain fires.

Noncombustibility and Material Properties

The fire resistance of MgO boards begins with their fundamental material properties:

• Inorganic Composition: Made primarily from magnesium oxide (MgO) and magnesium chloride (MgCl₂), with reinforcing fibers
• No Organic Content: Contains no wood pulp or other combustible materials
• High Thermal Stability: Maintains structural integrity at extremely high temperatures
• Low Thermal Conductivity: Slows heat transfer through walls and ceilings

High Temperature Performance

MgO boards demonstrate remarkable performance under extreme heat conditions:

Fire-Resistant MgO Boards: Testing and Standards

To ensure reliability in fire protection, MgO boards undergo rigorous testing to meet international standards. These tests verify their performance in real-world fire scenarios.

Key Fire Tests and Ratings

MgO boards typically achieve top ratings in these critical fire tests:

Certification and Compliance

Quality MgO boards should carry certifications from recognized testing laboratories:

• UL Certification: Underwriters Laboratories listings for specific assemblies
• ICC-ES Reports: Evaluation Service reports for code compliance
• CE Marking: Indicates compliance with European standards
• Local Building Code Approvals: Varies by country/region

Comparing MgO Boards to Other Materials

Understanding how MgO compares to traditional materials helps in making informed decisions for fire-resistant construction.

MgO vs. Gypsum and Cement Board

MgO vs. Plywood and OSB

Practical Benefits and Limitations

Fire Safety in Buildings

MgO boards contribute to passive fire protection systems by:

• Creating fire-resistant barriers between building compartments
• Protecting structural elements from premature failure
• Reducing smoke production during fires
• Minimizing toxic gas emissions

Installation and Maintenance

Installation Tips:

• Can be cut with standard drywall tools (utility knives, saws)
• Use corrosion-resistant fasteners (galvanized or stainless steel)
• Follow manufacturer's spacing guidelines for expansion
• Seal edges and joints properly

Maintenance: Virtually maintenance-free; doesn't require special treatments

Compliance and Drawbacks

Potential Limitations:

• Higher initial cost than gypsum or wood products
• Requires proper installation to prevent moisture issues (in some climates)
• Not all products are equal - quality varies by manufacturer
• May need additional structural support compared to plywood

Noncombustibility in Building Applications

Role in Fire-Resistant Construction

MgO boards serve critical functions in fire-safe building design:

• Exterior Wall Assemblies: As sheathing behind cladding systems
• Interior Partitions: Creating fire-rated walls between units
• Shaft Enclosures: Around elevators and stairwells
• Ceiling Systems: For fire-rated floor/ceiling assemblies

FAQ

What makes magnesium oxide sheathing board fire resistant?

MgO boards are inherently fire resistant because they:

1. Contain no combustible organic materials
2. Have high thermal stability (won't break down until extreme temperatures)
3. Release bound water when heated, which helps cool surfaces
4. Don't produce significant smoke or toxic gases

Can MgO boards be used outside?

Yes, quality MgO boards are suitable for exterior applications when:

• Properly sealed at edges and penetrations
• Installed with appropriate weather barriers
• Using exterior-grade products (some formulations are for interior only)

Do MgO boards need special tools for installation?

No, they can typically be installed with standard drywall tools:

Are MgO boards safe for indoor air quality?

High-quality MgO boards are generally safe because they:

• Contain no asbestos or formaldehyde
• Don't off-gas VOCs under normal conditions
• Are mold-resistant (won't support microbial growth)
• Look for products with GREENGUARD certification for verified low emissions