The question on the difference between CDX plywood and OSB comes up most of the time, raised by home owners and builders alike.
It is important to know the differences between CDX and OSB since it helps you to know:
- Which is better for a subfloor
- Between CDX and OSB what should you use for roof sheathing
- Can OSB and CDX be used outdoors?
- Are they susceptible to water damage?
What is CDX Plywood?
CDX plywood is a type of plywood that is commonly used in construction and woodworking projects. The “CDX” designation refers to its grading system, where “C” stands for the face quality and “D” stands for the back quality, while “X” indicates that the glue used in its construction is exterior-grade.
This means that CDX plywood has a rough appearance on one side (the “D” side) and a smoother, more finished appearance on the other (the “C” side). It is often used for structural applications like roof and wall sheathing, subflooring, and other projects where strength and durability are important.
The exterior-grade glue used in CDX plywood makes it suitable for use in outdoor and wet environments, providing protection against moisture and weather elements
What is OSB?
Oriented Strand Board also referred to as OSB, is an engineered wood product made by compressing and bonding wood strands or flakes with adhesives. These strands are oriented in specific directions during manufacturing to enhance the panel’s strength and durability.
OSB is commonly used in construction for applications such as roof and wall sheathing, subflooring, and as a base for various finishes. It offers cost-effective and versatile solutions for both residential and commercial building projects
The Differences between CDX and OSB
While OSB and CDX serve similar purposes, they have notable differences in composition, appearance, and applications:
Composition and Construction:
CDX plywood is a type of plywood made from thin layers or veneers of wood that are glued together in alternating directions. It typically has a solid wood core with an “A” or smooth side and a “D” or rough side. The layers are bonded with exterior-grade adhesive, making it durable and suitable for outdoor use.
In contrast, OSB is composed of wood strands or flakes that are oriented in specific directions, similar to a mat, and then compressed and bonded using adhesives. OSB panels have a distinctive appearance with visible wood strands on the surface.
Water Resistance
OSB (Oriented Strand Board) tends to be more water-resistant than CDX plywood, primarily due to its construction and the type of adhesives used in its manufacturing process.
OSB’s construction involves arranging wood strands or flakes in specific orientations and then bonding them with resins and adhesives under high pressure and heat. This process creates a tightly integrated panel with fewer gaps for water to penetrate. Additionally, the adhesives used in OSB manufacturing are often water-resistant or even waterproof, contributing to the overall water-resistant properties of the material.
CDX plywood, on the other hand, consists of thin layers or veneers of wood that are glued together. While the exterior-grade adhesive used in CDX plywood provides some level of water resistance, it may not be as effective at preventing water intrusion as the resins and adhesives used in OSB manufacturing.
It’s important to note that neither OSB nor CDX plywood is completely waterproof. Both materials can withstand some exposure to moisture, but prolonged or continuous contact with water can lead to swelling, warping, and deterioration over time.
To enhance water resistance and durability, it’s recommended to use appropriate coatings, sealants, or barriers, and to follow best practices for installation and maintenance in areas prone to moisture.
Appearance:
CDX plywood has a smoother and more finished appearance on its “A” side, making it suitable for applications where one side may be visible, such as subflooring.
On the other hand, OSB has a rough and textured surface due to the visible wood strands, giving it a distinct look. It is often used in applications where appearance is less important, such as roof and wall sheathing
Strength and Durability:
The CDX plywood is known for its structural strength and stability. It can withstand heavy loads and is commonly used in applications requiring strong, stable surfaces.
OSB is also strong and durable, with its strength derived from the oriented arrangement of wood strands. It offers good load-bearing capabilities and is widely used in construction.
Applications:
CDX plywood is good for applications where appearance matters, such as subflooring, underlayment, and areas where a smoother surface is desired.
OSB is good for structural purposes, including roof and wall sheathing, subflooring, and as a base for siding and flooring. Its rough appearance makes it suitable for applications where aesthetics are less important.
Why is CDX more expensive than OSB?
You will find that CDX plywood is more expensive compared to OSB. For CDX plywood, a 12 mm sheet typically costs $18, an 18 mm thick sheet costs around $ 25 while a thicker sheet such as 20 mm will typically cost up to $50. In contrast, for OSB, you will find that it is cheaper than CDX and almost half the price of CDX plywood. OSB board sheets typically start at about $13 for the thin sheets, and can go up to $30 for thicker sheets.
Here are some reasons why CDX plywood is more expensive than OSB:
Raw Material Availability and Costs:
The production of CDX plywood requires higher-grade veneers of wood, which can lead to higher raw material costs. OSB, on the other hand, is made from wood strands or flakes that are typically more readily available and may be sourced from lower-grade wood.
Manufacturing Process:
The manufacturing process for CDX plywood involves creating thin veneers of wood and gluing them together in layers. This process can be more labor-intensive and may require more energy and resources compared to the process of manufacturing OSB, where wood strands are oriented, bonded, and pressed.
Quality and Performance:
CDX plywood is often considered to have a higher quality appearance on its “A” side compared to the textured surface of OSB. Additionally, CDX plywood is known for its structural stability and strength, which can contribute to its higher cost.
Market Demand and Perception:
CDX plywood is often chosen for applications where appearance matters, such as subflooring or projects where one side will be visible. As a result, it might command a higher price due to its perceived quality and aesthetics.
Which is stronger OSB or CDX plywood?
For structural strength, OSB is generally considered to have comparable or slightly superior structural strength compared to CDX plywood. The construction of OSB adds strength in multiple directions making it a strong and stable material for load-bearing applications. These include structural panels, subflooring as well as roof and wall sheathing.
When it comes to bending and flexural strength, OSB panels have consistent mechanical properties throughout the panel. This provides superb bending and flexural strength. In comparison, CDX plywood may have slightly more variability due to variation in wood veneers used in its construction.
Besides, OSB also have better shear strength compared to CDX. As such, OSB is more suitable for applications where panels need to resist lateral forces including roofs and walls.
Finally, for edge holding and nail holding strength, CDX plywood has a better edge-holding capability due to the presence of wood veneers. This makes CDX advantageous for applications where nails and screws are used such as in subflooring.
The choice between the two should be based on the specific demands of your project, including load-bearing needs, intended use, budget, and aesthetics. For critical structural applications, consulting with a structural engineer or construction professional is advisable to ensure you select the appropriate material for your specific project requirements
