This strategy makes plywood stable and less likely to shrink, swell, cup or warp. There is always an odd number of layers in plywood panels so that the panel is balanced around its central axis. Throughout the thickness of the panel, the grain of each layer is positioned in a perpendicular direction to the adjacent layer. Resulting veneers have pure tangential grain orientation, since the slicing follows the growth rings of the log. The wood veneer is literally peeled from the log as it is spun. Imagine the raw log as a pencil being sharpened in a big pencil sharpener. Plywood is made from thin sheets of veneer that are cross-laminated and glued together with a hot-press. To begin with, the composition of each material is different. But, while the two products may perform the same structurally, they are undeniably different materials. The results of another independent study conducted by Raymond LaTona at the Weyerhauser Technology Center in Tacoma also showed that withdrawal strengths in osb and plywood are the same. Chow found that in both dry and 6-cycle aged tests: osb and waferboard performed equal to or better than CD-grade plywood. Professor Poo Chow, a researcher at the University of Illinois, studied the withdrawal and head pull-through performance of nails and staples in plywood, waferboard and osb. Even the storage recommendations are the same: keep panels off of the ground and protected from weather. However, 3/4-inch Sturd-I-Floor plywood weighs 70 pounds, 10 pounds less than its osb counterpart. The weights of osb and plywood are similar: 7/16-inch osb and 1/2-inch plywood weigh in at 46 and 48 pounds. Installation requirements prescribing the use of H-clips on roofs, blocking on floors and allowance of single-layer floor systems are identical. Both materials are installed on roofs, walls and floors using one set of recommendations. They share the same set of performance standards and span ratings. Osb and plywood share the same exposure durability classifications: Interior, Exposure 1 (95% of all structural panels), Exposure 2 and Exterior. And wood scientists agree that the structural performance of osb and plywood are equivalent. Likewise, APA the Engineered Wood Association, the agency responsible for approving more than 75% of the structural panels used in residential construction, treat osb and plywood as equals in their published performance guidelines. Codes recognize these two materials as the same. Model building codes typically use the phrase “wood structural panel” to describe the use of plywood and osb. Elmendorf Manufacturing Company made the first osb in Clairmont, NH just 14 years ago. Technology involving the random alignment of wood-fiber in waferboard soon gave way to the development of structurally superior oriented strandboard. Aspenite, the first generation waferboard (called chipboard by many builders), was manufactured from the abundant supply of aspen found in the region (credit julio). MacMillan Bloedel opened the first viable waferboard facility at Hudson Bay, Saskatchewan in 1963. Today, southern pine plywood accounts for about half of all structural plywood sold. In the late 1960’s advances in adhesive technology brought southern pine plywood to residential builders. The technical fix for delamination was inspired by the 1950’s housing boom. Delaminations were routine until waterproof synthetic resins were developed during world war II. This plywood, like all structural plywood made until the mid 1930’s, was bonded with non-waterproof blood and soybean glue. Portland Manufacturing Company made the first structural plywood from western woods in 1905. Many “old-timers” swore by solid board sheathing until the day they hung up their aprons. Delamination of early plywood sheathings gave plywood a bad name. Plywood suffered the same criticism not too long ago. Detractors of osb are quick to say: “osb falls apart”. Osb looks like, and is, a bunch of wood chips glued together. The issue for most builders who choose between plywood and osb is durability. Like it or not, osb will define the future of the structural sheathing market. But using panels made of wood chips makes some builders nervous. Manufacturers of oriented strandboard and plywood claim both products work well. Some information contained in it may be outdated. Please note: This older article by our former faculty member remains available on our site for archival purposes.