The Home Again crew toured the Willamette I-joist manufacturing facility for an up-close view of the fabrication process. The plant, which was built in 1990, produces approximately 55 million linear feet of I-joists a year.
I-joists are structural engineered building components that are used in place of traditional sawn lumber as floor joists. They are so called because they resemble an uppercase letter "I".
An I-joist is made by bonding a top and bottom flange with a web section. At the Woodburn, Oregon plant they use laminated veneer lumber (LVL) as the flange. LVL is an extremely high-strength product made from many layers of veneer, bonded together with resin. It is very straight and doesn't warp or shrink like regular lumber. With its dimensional stability and stiffness, it ensures floors that are straight and strong. When the LVL arrives at the plant, it is already cut to size.
The web, or middle sections, of the I-joist is oriented strand board (OSB). OSB is a composite panel made from small wood strands oriented in layers. The strands are oriented in a way that provides maximum shear strength in the I-joist. OSB is resource friendly as it utilizes deformed trees and thinnings that sawmills can't use. The OSB panels are cut into 4-foot lengths and then the edges are profiled in preparation for assembly.
Assembling the LVL and the OSB into one piece to make an I-joist is a highspeed process. First the LVL flange material is loaded into the assembler. As it travels down the assembly line, a rout is cut on the inside of the flanges and adhesive is applied in the rout.
About halfway down the line, pre-glued OSB web section is fed into the assembler. It combines with the flange to form a continuous I-joist. As the I-joist travels down the line, pressure is applied to the outside of the flanges to ensure a tight fit around the OSB web.
A cut-off saw cuts the I-joist to inventory lengths, then the I-joists are cured in a hot storage room at 100 degrees. This sets the adhesives.
Product quality is a constant consideration. Willamette monitors quality through internal process controls and exhaustive product testing to ensure the strength of its I-joists. Samples are taken several times each shift and tested to destruction to verify the integrity of the glued joints and make certain that the I-joists meet or exceed all design criteria and APA standards. While an I-joist is stronger than a solid 2x10, it uses half as much wood as a solid piece of lumber.
At the end of the process, the I-joistsd are nested, end-sealed, banded and wrapped for shipping. Their shape allows them to fit closely together for easy shipping.
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