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INTRODUCTION

Wood structural panels available today respond to changes in wood resources, manufacturing, and construction trends, meet designer needs for excellent strength, and are light weight while using the only renewable building material. A wood structural panel is a panel product composed primarily of wood, which, in its end use, is essentially dependent upon certain structural and/or physical properties for successful performance in service. Such a product is manufactured to standards that clearly identify its intended end use. Today, wood structural panels include plywood and mat-formed panels such as oriented strand board (OSB). Composite panels containing a combination of veneer and wood-based material have also been produced.

In the early days of plywood manufacturing, every mill worked with several species only and nearly identical technology. Manufacturing techniques didn't vary much from mill to mill. To produce panels under prescriptive standards, a mill used wood of a certain species, peeled it to veneer of a prescribed thickness, then glued the veneers together in a prescribed manner using approved adhesives.

As technology changed, mills started using a broader range of species and different manufacturing techniques. With the development of U.S. Product Standard PS 1-66 for Softwood Plywood - Construction & Industrial, three existing plywood standards were combined into one. And, for the first time, span ratings for construction uses were incorporated into the standard. The span rating concept would later be used as a basis for the development of performance standards.

At the same time, there was a growing need to increase efficient use of forest resources. Working in cooperation with the U.S. Forest Service, the American Plywood Association (APA) (now APA - The Engineered Wood Association) tested panels manufactured with a core of compressed wood strands and traditional wood veneer on the face and back for use in structural applications. By using cores composed of wood strands, manufacturers were able to make more efficient use of the wood resource and use a broader range of species. These panels are called composite panels.

In the course of the research on composite panels, performance standards were developed that led to a system of performance rated panels. Soon, manufacturers were making wood structural panels composed entirely of wood strands. Most current production of these panels, intended for use in structural applications, is referred to as oriented strand board, or OSB.