APA - The Engineered Wood Association

A Glossary of Engineered Wood Terms


Structural Plywood: The original structural wood panel, plywood consists of veneers arranged in perpendicular layers. The layers may consist of a single veneer ply or two or more plies laminated with the grain running in the same direction. There are always an odd number of layers, with the grain of the face layers typically oriented parallel to the long dimension of the panel. It is the cross-laminated layup of layers of veneer that gives plywood its excellent strength, stiffness and dimensional stability. In addition to a variety of sheathing, siding, sanded and concrete form grades, many manufacturers can produce custom layups for specialized applications.

Oriented Strand Board: OSB consists of wood strands bonded with adhesives to form a mat. Like the veneer in plywood, these mats are layered and oriented for maximum strength, stiffness and stability. The individual strands are typically three to four inches long. OSB is widely used as construction sheathing, as the web material for wood I-joists, as the structural membranes of structural insulated panels (SIPs), and in a growing number of other applications.

Structural Composite Panels: Structural composite panels (the APA tradename is COM-PLY) consist of veneer faces bonded to a wood-base core material, such as OSB. Composite panels are manufactured in three- or five-layer arrangements. A three-layer panel has a wood fiber core and a veneer face and back, while a five-layer panel also has a veneer crossband in the center. When manufactured in a one-step pressing operation, voids in the veneers are filled automatically by the particles or strands as the panel is pressed in the bonding process. Typical composite panel applications include sheathing, siding and industrial applications.


Glulam is an engineered stress-rated product created by bonding together individual pieces of lumber having a thickness of two inches (50 mm) or less. Individual pieces of lumber are end-joined together to create long lengths referred to as laminations. These laminations are then face-bonded together to create the finished product. Glulam is also among the most versatile of the engineered wood products. It can be shaped into forms ranging from straight beams to complex curved members, and is used in a wide variety of residential and nonresidential building construction applications, including headers, floor girders, ridge beams and purlins, cantilever beam systems, arches, domes and exposed applications such as bridges, marinas and utility structures.


Laminated Veneer Lumber (LVL): LVL is the most widely used of the structural composite lumber products. It is produced by bonding thin wood veneers together in a large billet. The grain of all veneers is parallel to the long direction. The LVL billet is then sawn to desired dimensions depending on the construction application. Some of the product’s many uses are headers and beams, hip and valley rafters, scaffold planking, and the flange material for prefabricated wood I-joists.

Parallel Strand Lumber (PSL): PSL consists of long veneer strands laid in parallel formation and bonded together with an adhesive to form the finished structural section. Like LVL and glulams, this product is used for beam and header applications where high bending strength is needed. PSL is also frequently used as load-bearing columns.

Oriented Strand Lumber (OSL): Similar to PSL, oriented strand lumber is made from flaked wood strands that have a high length-to-thickness ratio. Combined with an adhesive, the strands are oriented and formed into a large mat or billet and pressed. OSL is used in a variety of applications from studs to millwork components.


Also referred to as I-beams, wood I-joists are structural, load-carrying products. I-joists are typically available in long lengths and because they are very lightweight, they can be easily handled at the jobsite without the need for costly handling equipment. Their “I” configuration provides high bending strength and stiffness characteristics. The top and bottom flange material for I-joists is typically dimension lumber or laminated veneer lumber; the web material is OSB or plywood. Prefabricated wood I-joists are used extensively in residential construction for both floor and roof framing and are among the fastest-growing of the glued engineered wood products.

Learn More About APA Member Products

Get the latest information on APA member products, locate a member manufacturer near you, and download publications from the products section of apawood.org.

Rim Board
Specialty Wood Products