Plywood vs. MgO Board: Which Sheathing Is Right for You?
- JP Group MagMatrix Brand
- 18 hours ago
- 4 min read
Choosing the right materials is one of the most critical decisions in any construction project. The sheathing you select plays a huge role in your building's structural integrity, safety, and long-term durability. Two common but very different options are traditional plywood sheathing and modern Magnesium Oxide (MgO) board. While both can cover the frame of a structure, their properties and ideal uses vary significantly.
This guide will walk you through a detailed comparison of plywood and MgO board. We will explore their performance in key areas like fire and moisture resistance, overall durability, cost, and typical applications. By the end, you will have a clear understanding of which material best fits the needs of your project.
What is Plywood Sheathing?
Plywood is a familiar engineered wood product used in construction for decades. It is made by gluing together thin layers of wood veneer, called plies, with their grains arranged at right angles to one another. This cross-graining technique gives plywood its signature strength, stiffness, and resistance to shrinking or expanding.
It's a versatile and reliable material that has long been the standard for sheathing walls, roofs, and floors in both residential and commercial buildings. While standard plywood is combustible, it can be treated with fire-retardant chemicals to improve its performance in a fire.
What is MgO Board?
Magnesium Oxide board, often called MgO board, is a newer type of sheathing panel made from a mix of magnesium oxide, magnesium chloride, and other reinforcing materials like fiberglass mesh. Unlike wood-based products, MgO board is a mineral-based material, which gives it a unique set of properties.
It is primarily known for being inherently non-combustible and highly resistant to fire. This has made it a popular choice for projects with strict fire safety codes. In addition, its composition makes it resistant to moisture, mold, and insects, positioning it as a high-performance alternative to traditional sheathing.
Head-to-Head Comparison: Plywood vs. MgO Board
To make an informed decision, let's break down how these two materials stack up against each other across several important categories.
1. Fire Resistance
This is where the difference between the two materials is most dramatic.
Plywood: Standard plywood is a combustible material. It will catch fire and contribute fuel to a blaze. While fire-retardant treated (FRT) plywood is available and slows the spread of flames, the core material is still wood. FRT plywood buys valuable time for evacuation but will eventually burn.
MgO Board: MgO board is non-combustible. It does not burn and will not contribute fuel to a fire. It can withstand extremely high temperatures for extended periods, helping to contain a fire and maintain structural integrity. This makes it an excellent choice for fire-rated wall assemblies, commercial buildings, and multi-family residences where fire containment is a top priority.
Winner: MgO Board
2. Moisture and Mold Resistance
Water is a constant threat to building materials, leading to rot, mold, and structural failure.
Plywood: Plywood is vulnerable to moisture. If exposed to water or high humidity for prolonged periods, it can swell, warp, delaminate, and rot. It also provides an organic food source for mold and mildew to grow. While weather-resistant barriers and proper sealing help protect it, any failure in that system can lead to significant damage.
MgO Board: MgO boards are highly resistant to water. They do not swell or delaminate when exposed to moisture. Because they are inorganic, they do not support mold or mildew growth, making them an ideal choice for humid climates, basements, bathrooms, and other areas prone to dampness.
Winner: MgO Board
3. Strength and Durability
Sheathing adds rigidity and strength to a building's frame, so its durability is crucial.
Plywood: Plywood is known for its impressive structural strength and flexibility. Its cross-laminated structure allows it to resist bending forces and impacts well, making it excellent for bracing walls and providing a solid nail base. It can handle the typical stresses of construction and provides excellent shear strength, which is the ability to resist lateral forces like wind.
MgO Board: MgO board is very hard, rigid, and dense. It offers good compressive strength but can be more brittle than plywood. While durable, it may be more susceptible to cracking or shattering from a sharp, heavy impact. Its installation requires care, as over-driving fasteners can cause cracking around the screw or nail head.
Winner: Plywood (for structural flexibility and impact resistance)
4. Cost and Availability
Budget is a major factor in nearly every construction project.
Plywood: Plywood is a commodity building material that is widely available at most lumberyards and home improvement stores. As a result, it is generally the more affordable option. Its price can fluctuate based on lumber market conditions, but it typically remains a cost-effective choice for sheathing.
MgO Board: As a specialized, high-performance product, MgO board is more expensive than standard plywood. Its price can be two to three times higher per sheet. It may also be less readily available, sometimes requiring a special order from specific building material suppliers.
Winner: Plywood
5. Applications and Best Use Cases
The right material ultimately depends on the job it needs to do.
Plywood is ideal for:
Standard residential construction (walls, roofs, subfloors).
Projects where budget is a primary concern.
Applications requiring high shear strength and structural flexibility.
DIY projects due to its ease of use and availability.
MgO Board is the superior choice for:
Fire-rated assemblies in commercial and multi-family buildings.
Areas with high humidity or moisture exposure, like coastal regions or bathrooms.
Projects where mold resistance is critical, such as hospitals and schools.
As a tile backer or underlayment in wet areas.
Making Your Final Decision
Both plywood and MgO board are valuable building materials, but they serve different purposes. Your choice should be guided by your project's specific requirements, budget, and local building codes.
If you are working on a standard residential project where cost-effectiveness and proven structural performance are key, plywood remains an excellent and reliable choice. Its strength and affordability have made it a construction staple for a reason.
However, if your project demands superior fire safety, moisture and mold protection, or must meet strict building codes for non-combustible materials, then MgO board is the clear winner. The higher upfront cost is an investment in long-term safety, durability, and peace of mind, especially in challenging environments.
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