House Framing Test – OSB versus Plywood – What Should You Specify?

Foreword by Ian Thompson, Editor

House Framing Test I am always on the lookout for valuable insights that can help our readers make informed decisions when specifying building products in their construction projects. Today, we’re revisiting an older video by Matt Risinger who’s discussing the difference between plywood and OSB (Oriented Strand Board) sheathing for wall bracing and lining.

The reason we’re revisiting this video is we need to add another consideration into the mix, and that’s the fire retarding properties and health concerns of these two products.

For me, OSB is a great product, but it’s not my personal preference, I choose plywood over OSB. The reason for that is there is a lot less glue and it outperforms OSB in a fire.

Considering fire alone, I believe OSB to be a far inferior when considering structural integrity during a fire. OSB reaches its ignition temperature far sooner than plywood because of their physical structures and glues, with Plywood being more solid.

10 – 15 years ago people had approx. 10 minutes to escape a house fire once alerted by a smoke detector. Today, that time is believed to have decreased to as little as 4 -6 minutes (depending on manufacturers glues used). These glues in OSB manufacture often burn hotter and faster than plywood. This is also a danger to firefighters because it means quicker structural failure. A hotter fire also means more damage which normally results in complete loss. So when you consider poor fire performance, is OSB really cheaper?

One of the standout points in the video is the emphasis on building durable homes that stand the test of time — homes that you can proudly showcase to future generations. Matt shares practical insights drawn from years of experience in both new construction and remodeling, highlighting common pitfalls and best practices.

A quick comment about Gypsum board, it’s a good product with good fire-retarding properties, but personably, I don’t like using it on building projects because it hates moisture, and once wet needs replacing. It also breaks easily on site, and when I’m attaching anything to a wall I prefer the strength that a wooden board gives me over paper.

Over to Matt.

House Framing Test – OSB versus Plywood – Video Summary

House Framing Test – Understanding the Differences Between Plywood and OSB Sheathing in Home Construction

When building a custom home, one of the greatest advantages is the ability to make choices that align with your vision and standards. Not only can you select the perfect countertops or fixtures, but you also have the freedom to decide on the fundamental materials that make up the bones of your house. One critical decision you’ll face is choosing between plywood and OSB (Oriented Strand Board) for your home’s exterior sheathing. Let’s dive into the differences between these two popular options and explore how each can impact the durability and longevity of your new home.

Why the Choice of Sheathing Matters

Before we delve into plywood and OSB, it’s essential to understand why the choice of sheathing is so significant. Sheathing serves as the skin of your house, providing structural support, rigidity, and a base for applying exterior finishes. It plays a crucial role in protecting your home from the elements and ensuring its durability over time.

While some production builders might opt for less expensive alternatives like certain cardboard products (which we won’t name to keep things fair), these materials often fall short in terms of air tightness, waterproofing, and overall longevity. As someone investing in a custom home, you likely value quality and durability over minimal cost savings. After all, you want a home that not only looks beautiful but stands the test of time—a place you can proudly show your grandchildren decades down the line.

A Brief History of Sheathing Materials

To appreciate the modern choices available, it’s helpful to look back at how home construction has evolved:

Solid Wood Sheathing (Shiplap): Before the advent of engineered wood products, homes were typically sheathed with solid wood boards like shiplap. Builders would install these boards one at a time, creating a sturdy exterior that offered both structural support and resistance to racking (that’s when a house shifts or leans due to wind or seismic forces). While solid wood sheathing was robust, it was also labor-intensive and time-consuming to install.

Plywood Emerges Post-World War II: Around World War II, plywood became a game-changer in the construction industry. With a housing boom on the horizon, builders needed materials that were quicker to install yet still provided strong structural integrity. Plywood offered just that. Composed of multiple layers (or plies) of wood veneer glued together, plywood provided excellent strength and was easier to handle than individual boards.

OSB Gains Popularity in the 1980s: Although OSB was invented in the 1960s, it wasn’t until the 1980s that it became a prominent choice in residential construction. Made from small, fast-growing trees, OSB utilizes wood strands that are oriented, glued, and pressed together under heat to form boards. Today, OSB accounts for about three-quarters of the sheathing used in custom homes in the United States.

Breaking Down the Options: Plywood vs. OSB

Let’s examine each material more closely, considering factors like composition, cost, and performance.

Plywood

Composition: Plywood consists of thin layers of wood veneer, known as plies, glued together with the grain of each layer perpendicular to the one below. This cross-graining technique gives plywood its strength and reduces the likelihood of splitting when nailed at the edges.

Types: Plywood comes in various thicknesses, commonly half-inch and five-eighths-inch sizes. The number of plies can vary, typically ranging from three to five for half-inch plywood and four to seven for five-eighths-inch plywood.

Cost: At the time of discussion (early 2018), a standard half-inch sheet of CDX plywood (commonly used for sheathing) costs about $18. While prices fluctuate with the market, plywood generally remains more expensive than OSB.

OSB (Oriented Strand Board)

Composition: OSB is made from small wood strands extracted from fast-growing trees. These strands are mixed with adhesives, oriented in specific directions for strength, and then compressed under heat to form sheets.

Popularity: With about 75% market share in custom home construction sheathing, OSB is a widely accepted and used material. Its manufacturing process allows for efficient use of wood resources, making it an environmentally conscious choice.

Cost: A standard half-inch sheet of OSB costs around $12, making it a more budget-friendly option compared to plywood.

Cost Considerations in Real Terms

Understanding the cost difference is crucial, but it’s also important to put those numbers into perspective concerning the overall budget:

Example Scenario: Imagine you’re building a 7,000-square-foot home (including garages and porches). Such a project might require approximately 200 sheets of exterior sheathing.

Calculating the Difference: Choosing OSB at $12 per sheet would total $2,400. Opting for plywood at $18 per sheet brings the total to $3,600.

Budget Impact: The $1,200 difference might seem significant at first glance. However, when spread over the total cost of building a custom home, especially one of considerable size, this price difference becomes a relatively small percentage. It’s an investment in the long-term performance and durability of your home.

Performance Over Time

Cost is just one factor; performance and longevity are paramount when selecting sheathing for your home.

Plywood’s Advantages and Considerations

Moisture Handling: Plywood can absorb small amounts of moisture without significant degradation. Its layered construction allows it to handle incidental water exposure better than OSB in some cases.

Drying Potential: If plywood gets wet but can dry out, it often returns to its original state without losing structural integrity. This characteristic provides a buffer against minor leaks or condensation issues.

Risk of Rot: However, if plywood remains wet and cannot dry—perhaps due to improper waterproofing or constant exposure—it can rot over time. Proper installation and moisture management are critical.

OSB’s Strengths and Limitations

Structural Performance: OSB provides excellent structural support and is less susceptible to issues from small, incidental moisture exposure. Its uniform composition means it doesn’t have natural defects like knots, which can be present in plywood.

Moisture Sensitivity: OSB is generally more sensitive to prolonged moisture exposure compared to plywood. If OSB gets wet and cannot dry out, it may swell or degrade more quickly.

Longevity: When kept dry, OSB can perform exceptionally well over the long term. Proper sealing and weatherproofing are essential to ensure its durability.

The Importance of Proper Waterproofing

Regardless of whether you choose plywood or OSB, the key to longevity is effective waterproofing and moisture management. Homes today are built to be more airtight and energy-efficient than in the past, which means they don’t naturally allow for moisture to escape through drafts or poor insulation.

Critical Areas to Focus On:

Windows: Windows are common points of water intrusion. Over time, even high-quality windows can develop leaks. It’s crucial to install proper flashing and sealing around windows to prevent water from penetrating the sheathing.

Bottom of the House: The first two feet of the exterior are especially vulnerable to splashback from rain and ground moisture. Taking extra precautions in this area, such as additional waterproofing measures or using more robust materials, can help prevent long-term issues.

Sealing Penetrations: Any openings for utilities, vents, or fixtures must be carefully sealed to prevent water and air infiltration.

Creating a Durable Building Envelope

Your home’s exterior sheathing is part of a larger system known as the building envelope, which includes siding, insulation, vapor barriers, and more. Ensuring each component is properly installed and works in harmony is essential.

Weather-Resistant Barriers (WRBs): Applying a high-quality WRB over your sheathing adds a crucial layer of protection against moisture and air leaks.

Proper Installation Practices: Following best practices for installation, such as using appropriate fasteners, sealing joints, and accommodating for expansion and contraction, will enhance the performance of your sheathing.

Ventilation and Drainage: Incorporating features that allow for ventilation and drainage behind the siding can help any incidental moisture to escape, reducing the risk of rot or mold.

Making the Right Choice for Your Home

In the end, both plywood and OSB can be excellent choices for your home’s sheathing if installed correctly and protected from moisture. Your decision may come down to factors like budget, personal preference, and specific project requirements.

Considerations for Plywood:

Slightly higher cost.

Better performance in some moisture scenarios.

Generally better performance in fires than OSB

Traditional choice with a long history of use.

Considerations for OSB:

More cost-effective.

Widely used with proven structural capabilities.

Requires diligent moisture management.

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