Laminated veneer lumber (LVL) is manufactured by bonding thin wood veneers together under heat and pressure. Once it is fabricated into billets of various thicknesses and widths, it can be cut at the factory into stock for headers and beams, flanges for prefabricated wood I-joists, or for other specific uses. Veneer thicknesses range from 2.5mm (0.10") to 4.8mm (3/16") and common species are Douglas fir, larch, southern yellow pine and poplar.
The distinguishing difference between LVL and plywood is in the orientation of the plies as shown in Figure 1 below. Plywood is cross-laminated, meaning that the grain of each veneer layer runs at 90 degrees to adjacent layers. This enables the panel to be relatively strong in both the wide and narrow directions when loaded on the sheathing face. However, when loaded on the edge as a beam, plywood is not as strong as the same cross section of LVL because not all of the plies are longitudinal to the beam.
Figure 1: Ply Orientation of LVL
In LVL, the grain of each layer of veneer runs in the same (long) direction with the result that it is strong when edge loaded as a beam or face loaded as a plank. This kind of lamination is called parallel-lamination.
LVL is a solid, highly predictable, uniform lumber product because natural defects such as knots, slope of grain and splits have been dispersed throughout the material or have been removed altogether. It is made of dried and graded veneer which is coated with waterproof adhesives, assembled in an arranged pattern, and formed into billets by curing in a heated press.
One leading manufacturer grades the veneers with advanced ultrasonic grading technology in addition to visual grading. Dependent on the end use of the LVL product the ultrasonically graded veneers are specifically located in the material to utilize efficiently the strength characteristics. For example, if the end use of the LVL product is scaffold plank, the higher grade veneers will be placed at the outer faces of the plank.
LVL was first used during World War II to make airplane propellers, and since the mid-1970s, has been available as a construction product for beams and headers where high strength, dimension stability, and reliability are required.
The veneering and gluing process of LVL enables large members to be made from relatively small trees thereby providing for efficient utilization of wood fibre. Like other products made by laminating pieces of wood together to create a structural element such as plywood, glulam, parallel strand lumber (PSL), or OSB/waferboard, LVL offers the advantages of higher reliability and lower variability through defect removal and dispersal.
LVL is used primarily as structural framing for residential and commercial construction and is well suited to applications where open web steel joists and light steel beams might be considered.
Finished or architectural grade appearance is available from some manufacturers, usually at an additional cost. However, when it is desired to use LVL in applications where appearance is important, common wood finishing techniques can be used to accent grain and to protect the wood surface. In finished appearance, LVL resembles plywood or lumber on the beam face.
Other uses include scaffold planking and as flange members for some proprietary prefabricated wood I-joists.
LVL has also been used as distribution and transmission cross arms in utility structure box shaped roadway sign posts, and as truck bed decking with hardwood face veneers.
LVL can easily be cut to length at the jobsite. The fastening and connection details and requirements are similar to those of solid sawn lumber. However, all special cutting, notching or drilling should be done in accordance with manufacturer recommendations.