Wood I-joists are proprietary products and the method of manufacture varies somewhat from one manufacturer to another. A general representation of the manufacturing process is shown in Figure 3.21 below.

As in the manufacture of other engineered wood products, moisture control of the flange and web material is important to ensure optimum gluing conditions, and dimensional stability of the finished product. All material must be dry, with an equilibrium moisture content (EMC) in the range of at least 8 percent and no more than 18 percent. It must also be conditioned to room temperature of at least 10°C (50°F).  

Prior to assembly, the solid sawn flange material is fingerjoined into long lengths (no butt joints are allowed in the flanges of prefabricated wood I-joists). A groove for acceptance of the web is routed into one face of the flange material.

The web material is cut to the size required to give the appropriate depth to the assembled wood I-joist. The web ends that form the web joints are cut or machined as required and the web edges that mate with the flanges are machined, shaped or crimped as required.

Adhesive is spread on the web ends to form glued web joints and adhesive is placed into the flange routs to form a glued flange to web connection. The top and bottom flanges are of equal specified lengths and are end aligned with one another, prior to joist assembly. The flanges are pressed onto the long edges of the webs just after the web joints are mated to complete assembly of the joist.

Prior to curing, the assembled joists are cut to specified lengths. The joists are generally placed in a low temperature oven or curing environment (21 to 65°C (70 to 150°F)) for a specified period to insure proper cure of the adhesive.

After curing, the product is inspected and then bundled and wrapped for temporary storage or shipment.

Figure 3.21: Manufacture of Prefabricated I-Joists

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