Prefabricated wood I-joists belong to a family of wood products known as an engineered wood products (EWP’s). Other EWP’s include Glulam Beams, Structural Composite Lumber (SCL), finger jointed lumber and Structural Panels. SCL includes products such as Laminated Veneer Lumber (LVL), Parallel Strand Lumber (PSL), and Laminated Strand Lumber (LSL). Structural panels include products such as Oriented Strand Board (OSB) and plywood.
Prefabricated wood I-joists are made from EWP’s. The flanges are typically SCL or finger jointed lumber while the webs are either OSB or Plywood and fall under this classification. All of these components can be produced from fast growing, small diameter, low quality trees. In addition, EWP’s utilize tree species once deemed to be “weed trees”.
Because of the small size of these trees, it would be impossible to make sawn lumber that is greater than the diameter, but EWP’s make it possible to utilize this resource. The question then becomes, how can a high strength and high quality product be created from such resources? The flanges are designed for stiffness to resist bending forces and the web is designed to withstand shear forces. The design of the prefabricated wood I-joist takes the geometry of the I-shaped cross section to optimize each component so that the wood fiber is efficiently utilized.