Should I use CDX or OSB for Roofing Plywood?

OSB is much more waterproof than plywood and CDX plywood. The glue and resin that is mixed in with the wood chips makes it much less permeable, so OSB holds up longer in harsher conditions. That is why OSB is sometimes used to secure houses when a hurricane draws near.

 

When planning to repair or replace your roof, you'll likely encounter different types of plywood materials—most commonly OSB and CDX. At first glance, these abbreviations might seem confusing, and it's natural to wonder: What do they mean? What's the difference between them? And more importantly, which one is better suited for roofing?

 

Although OSB and CDX may serve similar functions, they differ in composition, appearance, and performance. Each has its own strengths, making it more suitable for certain applications over the other.

 

In this guide, we'll explore the key differences between CDX and OSB to help you make an informed decision for your roofing project.

 

 

About CDX Plywood

 

CDX plywood is a type of veneer plywood made by gluing and pressing multiple layers of wood together, with each layer's grain oriented perpendicular to the one below. This cross-grain construction adds strength and stability. The letters "C" and "D" refer to the grades of the plywood's face and back surfaces, indicating the quality of each side, while the "X" stands for "exposure," meaning the plywood is intended for limited outdoor use where it may be exposed to moisture temporarily.

 

Thanks to its layered construction, CDX offers excellent structural integrity, making it a stable and durable choice for many construction applications.

 

About OSB (Oriented Strand Board)

 

OSB is manufactured quite differently from CDX. It's made by compressing layers of wood strands—combined with adhesives and resins—into a solid panel, which is then heat-cured to form a strong, uniform board. This production method makes OSB more cost-effective, typically priced at about half the cost of CDX.

 

Early forms of OSB, known as waferboard, had limited performance and durability. However, modern OSB has seen significant improvements, offering reliable strength and moisture resistance, making it a competitive alternative in many structural applications.

 

Differences Between OSB and CDX for Roofing Plywood

 

Let's take a closer look at how CDX and OSB differ when used as roofing plywood, particularly in terms of moisture resistance—one of the most critical factors in roofing applications.

 

Moisture Resistance

 

One key difference between OSB and CDX is how each material responds to moisture. The "X" in CDX stands for "exposure," not "exterior"—a common misconception. This means CDX plywood is rated for limited exposure to moisture, not for long-term outdoor use. For example, when used in subflooring, CDX can withstand short-term exposure to water, but it must be covered or sealed for extended durability—often with a layer of OSB or other protective material.

 

Because of its limited water resistance, CDX is best suited for interior applications where moisture is not a major concern. It is generally not recommended for use in roofing, outdoor sheds, or any environment subject to regular exposure to rain or humidity—unless you're using pressure-treated CDX, which is chemically treated to resist decay and can last for decades even without a protective coating.

 

Sheathing

 

OSB is widely regarded as an excellent material for sheathing in residential construction. Contractors commonly use it for both roofing and subflooring due to its strength, affordability, and ease of installation. Some modern OSB panels even come with integrated weather-resistant barriers or building wraps, which simplify the construction process—often requiring nothing more than sealing the seams with tape for added protection.

 

OSB is much more waterproof than plywood and CDX plywood. The glue and resin that is mixed in with the wood chips makes it much less permeable, so OSB holds up longer in harsher conditions. That is why OSB is sometimes used to secure houses when a hurricane draws near.

 

Dimensional Stability

 

Although OSB is often considered water-resistant, its moisture behavior has some drawbacks. It doesn't absorb water quickly, but once it does, it retains that moisture for a long time and dries out slowly. As a result, OSB can swell and may not return to its original dimensions, potentially affecting structural integrity over time.

 

In contrast, CDX plywood readily absorbs moisture but also dries out quickly. More importantly, it tends to return to its original shape and thickness with minimal warping. This gives CDX better dimensional stability, making it a preferred choice for interior structural components where precise fit and form are critical.

 

Cost

 

From a budget standpoint, OSB is generally the more economical option. It typically costs less than CDX and is widely available at most hardware stores and lumberyards. For builders looking to reduce costs without compromising too much on performance, OSB is often the go-to material for sheathing and general-purpose applications.

 

Overall Application

 

Taking all the above factors into account, the key question remains: Which is better for roofing—OSB or CDX? While some may prefer CDX, many building professionals consider OSB the more practical choice for roofing applications.

 

OSB tends to be more dimensionally stable over time, as it's less prone to expanding and contracting with changes in humidity, even though it takes longer to dry once wet. When paired with proper weatherproofing—such as underlayment or building wrap—OSB holds up well against the elements. Additionally, shingles provide an extra layer of protection that further shields OSB from moisture.

 

In contrast, even when covered with shingles, CDX is more vulnerable to prolonged moisture exposure. It can delaminate and warp over time, increasing the risk of leaks and structural issues. For these reasons, OSB is often the preferred material for long-term roofing performance.

 

CDX vs. OSB: Which is Right for Your Project?

 

Choosing between CDX and OSB starts with understanding their core differences—especially in areas like moisture resistance, cost, and manufacturing methods. Each material has unique properties that make it better suited for specific applications. OSB is often favored for its affordability and wide availability, while CDX is preferred in scenarios where durability and dimensional stability are top priorities.

 

Still unsure which option is best for your roofing project? Our experienced team is here to help. Contact us today through the form on our website, and we'll be happy to offer expert advice tailored to your needs. We look forward to assisting you!