Is gypsum board considered a combustible material?

In the construction industry, gypsum boards—also called plasterboards, drywall, or gypsum wall panels—are one of the most common materials used for interior walls and ceilings. Due to their excellent workability, sound and thermal insulation properties, and relatively low cost, gypsum boards are widely used in residential, commercial, and industrial buildings.

However, a common question arises when selecting building materials: Are gypsum boards combustible? Will they burn in a fire? Can they provide effective fire protection in buildings?

Answering this requires examining multiple aspects: the material composition and properties, inherent combustibility, relevant standards and testing methods, and the practical role of gypsum boards in fire protection design. This article systematically addresses these issues and explains why gypsum boards, while largely non-combustible, cannot be considered completely fireproof in all circumstances.

Composition and Physical Properties of Gypsum Boards

To assess combustibility, it is important to understand the material’s composition and structure. Traditional gypsum boards generally consist of:

Gypsum core: Composed of calcium sulfate dihydrate (CaSO₄·2H₂O), an inorganic mineral.

Paper facings: Front and back layers of paper provide structural strength and facilitate finishing and installation.

The gypsum core is inherently non-combustible, and its chemically bound water contributes significantly to fire resistance. When exposed to high temperatures, this water absorbs heat and evaporates, slowing temperature rise and flame propagation.

Thus, the fire-resistance mechanism of gypsum boards comes from the material’s composition and thermal behavior, rather than from flame retardants or chemical additives.

Definitions of Combustible and Non-Combustible Materials

In building fire codes, combustibility refers to whether a material can sustain burning when exposed to heat or flame. Common test methods include:

ASTM E136: Tests materials in a high-temperature furnace at 750 °C. Materials that do not sustain combustion or produce continuous flames are considered non-combustible.

ASTM E84: Measures surface flame spread and smoke development to evaluate decorative or surface materials.

Combustible materials, such as wood and plastics, ignite and release energy when exposed to flame. Non-combustible materials do not sustain burning under defined high-temperature conditions, or decompose without contributing to the fire.

Combustibility Testing and Classification of Gypsum Boards

Gypsum Core Is Non-Combustible

Gypsum itself is classified as a non-combustible inorganic material because:

Its chemically bound water absorbs heat and slows heat transfer during high-temperature exposure.

Its mineral structure meets non-combustible standards in tests such as ASTM E136.

This means the core alone does not provide fuel or promote fire spread.

Overall Board Classification

Many building codes adopt a composite approach:

Layered materials can be considered non-combustible if the core passes non-combustibility tests and surface layers (such as thin paper facings) do not significantly contribute to flame spread.

ASTM E84 tests show gypsum boards have very low flame spread ratings, indicating they do not burn rapidly or propagate fire.

Paper Facings Are Combustible, but Limited

While the gypsum core is non-combustible, the paper facings are combustible:

The paper may ignite when exposed to direct flame.

However, the gypsum core prevents sustained flame propagation.

Most codes consider the overall fuel contribution of the paper facings to be minimal.

Thus, gypsum boards are not entirely non-combustible, but they are typically classified as non-combustible or limited-combustible materials.

Gypsum Boards and Fire Protection

Not a Complete Fireproof Wall

It is a misconception that gypsum boards alone provide fireproofing. Key points:

Fire resistance is measured for the entire assembly (walls, partitions) under standard fire tests, such as ASTM E119.

Tests account for structural supports, insulation, gypsum boards, joints, and finishes.

Even though the core is non-combustible, improper installation can compromise overall fire performance.

Different Types of Gypsum Boards

The fire performance varies depending on board type:

Standard Gypsum Board

Used for general interior partitions or ceilings.

Relies on gypsum core and paper facings for fire resistance.

Provides limited delay in flame spread but cannot independently achieve high fire ratings.

Fire-Rated or Fire-Resistant Gypsum Board

Designed for higher fire-resistance requirements.

Features include thicker boards, reinforced cores (e.g., glass fiber), higher density, or special formulations.

When incorporated into walls, these boards can achieve 1–2 hours or more of fire-resistance ratings.

Such boards remain non-combustible but enhance the performance of the overall system and are used in fire barriers and escape routes.

 Classification in Building Codes

Non-combustible:

Gypsum core passes non-combustibility tests.

Boards are allowed in locations requiring non-combustible materials, such as high-rise interior walls and ceilings.

Limited-combustible:

Due to paper facings, some codes classify gypsum boards as limited-combustible.

The paper may burn under extreme conditions, but the material does not significantly fuel a fire.

Fire Performance in Real Fires

Heat absorption and evaporation:

The chemically bound water in gypsum absorbs heat during high temperatures, slowing flame propagation and maintaining lower board temperatures.

Slow flame spread:

ASTM E84 testing shows low flame spread indices, making gypsum boards a safe wall covering.

Paper layer combustion:

Paper facings may char or ignite, but the gypsum core prevents sustained burning.

System integrity matters:

Actual fire resistance depends on the full wall or partition system, not just the board alone.

Gypsum core is non-combustible: Calcium sulfate dihydrate is inorganic, and its water content absorbs heat to slow fire spread.

Overall board is typically non-combustible: Paper facings may burn but do not significantly contribute fuel.

Combustibility classification requires testing: Standards like ASTM E136 and ASTM E84 confirm the core’s non-combustibility, though some boards are classified as limited-combustible.

Gypsum board alone is not a fireproof wall: Fire resistance depends on the entire assembly, including structural and insulating components.

In conclusion, gypsum boards are widely used in interior walls and ceilings because they are non-combustible or limited-combustible and provide effective heat delay during fires. However, evaluating combustibility and fire resistance requires considering the board type, installation, and overall wall assembly according to code requirements.