Plywood vs OSB Sheathing | What’s the best sheathing for homes?

February 23, 2022

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Plywood and OSB are two of the most popular engineered wood products. They were used as sheathing for walls, floors and roofs in homes in the 70s and 80s, but nowadays, they are mainly used for custom homes.

Plywood Manufacturing Process

Plywood is aptly named, as it comprises thin layers or plies of wood veneer. The manufacturing process involves the following steps:

Debarking: Tree trunks are placed on a conveyor belt and sent to debarkers, where the bark is removed using sharp-toothed grinding wheels or high-pressure water jets.
Softening: To enhance the wood’s pliability, the logs are heated and soaked in hot water for over 12 hours.
Veneer Creation: A lathe rotates the log while a knife peels a continuous sheet of veneer 1/8″ thick.
Drying: The veneers are cut into 4×8 sheets and dried at 400°F.
Gluing and Layering: The veneers are run through a glue curtain, coating all sheets except the topmost one. These veneers are then layered cross-grain and pressed under high pressure, binding them together with the heated glue.

Properties of Plywood

Plywood’s strength is attributed to its cross-graining, where the grain on the top and bottom surfaces runs lengthwise, while the layers beneath run at 90 degrees. This unique structure prevents splits when nailed at the edges, reduces expansion and shrinkage, and enhances stability. Plywood is graded from A to D, based on the quality and appearance of the top and bottom veneers, with A-grade plywood commonly used for furniture and D-grade for sheathing.

OSB Manufacturing Process

As the name suggests, OSB consists of strands of wood oriented in different directions. The manufacturing process involves the following steps:

Stranding: Trees are debarked and then placed on a machine called a strander, which cuts the trees into strands of specific width, thickness, and length.
Drying: The strands are then dried to reduce moisture content.
Blending and Layering: After drying, the strands are blended in a rotating drum with resins and wax. Long strands on the top and bottom face one way, while short interior strands face the opposite direction.
Pressing: Eight-inch-thick mats are pressed at 600 psi, and the heat cures the resin. The OSB boards are then cut to the correct length and width.

Properties of OSB

OSB’s strength lies in its cross-oriented layers, making it consistent and durable. It boasts a shear value twice that of plywood and comes in four main types, with the best suited for I-beams, subfloors, and roofs, and the worst used for packing and furniture. Due to its composition, OSB has a rougher appearance and surface texture than plywood, and its larger panels make it a suitable choice for sheathing, floors, and joists.

Comparison

Appearance: Plywood is versatile and available in different thicknesses and wood types. On the other hand, OSB has a rougher appearance and is typically made of fast-growing pine and poplar wood.
Installation: Both plywood and OSB hold nails and screws in place, but cutting OSB can be messier, with edges more prone to splintering.
Cost: Prices of both plywood and OSB have fluctuated significantly in recent years, making it challenging to determine which is more cost-effective.
Water Resistance: Plywood generally offers better water resistance, while OSB has been improved over time and now includes water-resistant options like Advantech.
Health: Plywood can off-gas urea formaldehyde glue, while OSB may contain various moisture-resistant binders that emit VOCs (volatile organic compounds).
Fire Resistance: Plywood and OSB have varying levels of fire resistance, with some types offering better performance when exposed to flames.

Conclusion

Both plywood and OSB are impressive inventions that provide excellent alternatives to solid hardwood. Each offers unique characteristics and applications, making them valuable choices for different projects. Plywood excels in DIY furniture projects, while OSB’s consistency and sustainability make it a promising option for modern construction. To ensure the best results, consider the specific needs of your project and choose high-quality plywood or OSB from reputable brands. With proper installation and maintenance, these engineered wood products can add durability and functionality to your home.