What’s the Difference? Plywood vs OSB

- Dec 24, 2020-

What’s the Difference? Plywood vs OSB

Though building codes treat both materials equally as “structural panels,” plywood and oriented strand board (OSB) are quite different compositionally. Plywood is made from glued thin strips of wood veneer (called plies) that are layered at alternating 90-degree angles and placed in a hot press; the resulting cross-laminated and layered material is structurally enhanced and resistant to the expansion and contraction that affects solid wood. OSB, on the other hand, consists of 3-inch to 4-inch strands of wood that are also layered and configured in a crossing pattern, then glued and pressed.

Plywood vs. OSB

Which is the better option, plywood vs. OSB? Well, each has their own strengths and weaknesses when used as exposed decking or subflooring.

  • OSB is considered more structurally consistent than plywood. Since a sheet of plywood consists of several large veneers of wood, it’s susceptible to instances of knots and other imperfections (which, if aligned, could create slightly softer spots throughout the material). Meanwhile, OSB compacts as many as 50 layers of strands into a single sheet the same thickness as that plywood, ensuring a much denser—and heavier—product throughout.

  • OSB absorbs less moisture, but plywood dries out faster and more completely. How the subfloor materials react to water matters during both an open-air construction phase of a house as well as homeownership when a leak or flood might compromise the subfloor. Slower absorption of moisture is ideal for throwing a tarp out over an unprotected subfloor or catching a leak before real damage. But OSB also takes a longer time to dry out, giving the trapped moisture more time to degrade the material than a quick-drying plywood subfloor.

  • OSB does not have the delamination issues that can plague plywood, but it’s prone to edge swelling when exposed to moisture. Though both are examples of laminated wood (meaning that each consists of thin sheets of wood that have joined with glue and compressed into a larger, rigid sheet), water damage is more likely to cause plywood’s glue to fail and its layers to bubble. This swelling effect can disappear when the plywood dries completely without impacting its structural integrity. OSB’s biggest weakness is at its edges, which will remain swollen even after the board has dried. In fact, due to the problems that edge swelling creates underneath a finished floor, a couple of national ceramic tile associations have discouraged the use of OSB as a subfloor or underlayment below a tile floor.

  • OSB generally costs less than plywood. Sure, the cost of any wood product will fluctuate by region and supply, but this cost comparison generally holds water. It’s the reason a good number of high-volume builders had turned to OSB. The cost of plywood will vary depending on wood species, a factor that can also affect performance. For either of these materials, enhanced versions (which are detailed in the next section, “Understanding the Upgrades”) will cost more, but the savings come in time and materials. The enhanced plywood or OSB installation should survive exposure to moisture, meaning builders likely won’t need to install a partial replacement or second subfloor in order to install finish flooring.